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Effect of exogenous enzymes on sensory quality of pre-conditioned tuna fish steak
Qihang CHEN, Yuxuan XIAO, Xubo FANG, Xiao'e CHEN
 doi: 10.12131/20210080
[Abstract](62) [FullText HTML](18) [PDF 722KB](0)
To solve the problems of low level of deep processing and utilization of tuna products, and to develop tuna processing products, we used yellowfin tuna (Thunnus albacares) as raw material to compare the effects of flavor protease, neutral protease, alkaline protease, papain and lipase on the amino acid nitrogen content and sensory score of pickled tuna. On the basis of single factor experiment, we determined the best salting conditions for tuna by orthogonal test, and carried out a correlation analysis of tuna before and after salting with electronic nose. The results show that the flavor protease was the best exogenous protease, and the best processing fomula was: 0.3% flavor protease, 50 ℃ and 3.5 h. Under these conditions, the mass fraction amino acid nitrogen was 0.82 mg∙g−1, and the sensory score was 36.3. The meat of pickled yellowfin tuna steak was delicious with good flavor.
Trophic structure of fishery organism assemblage in Daya Bay based on carbon and nitrogen stable isotope analysis
Huijuan WANG, Wenbo ZHANG, Honghui HUANG, Shannan XU, Huaxue LIU
 doi: 10.12131/20210005
[Abstract](131) [FullText HTML](19) [PDF 1360KB](21)
According to the biological survey of bottom trawl fishery conducted in Daya Bay in the summer of 2017 and the winter of 2018, we analyzed the basic characteristics of the stable isotope of carbon and nitrogen δ13C and δ15N in fishery organisms by using δ13C and δ15N techniques. In addition, we constructed a continuous trophic level spectrum, and discussed the differences in the nutritional structure of fishery organisms in different seasons. The results show that the range of (δ13C and δ15N) of main fishery species in Daya Bay were −19.66‰−15.19‰ [Average: (−17.26±0.86) ‰] and 11.63‰−16.01‰ [Average: (13.59±0.96) ‰], respectively. We used the average δ15N of small zooplankton as a reference to construct the trophic level spectrum of fishery organisms, and found that the trophic level of fishery organisms in Daya Bay ranged from 2.99 to 4.28. The trophic level of fish had the widest span and a more complex diet. We calculated seven quantitative community indices of trophic structure of macrobenthos by using the SIBER model, and found that some organisms shared the preys, and there was a phenomenon of niche overlap. In addition, the community nutrition redundancy in summer was lower than that in winter.
Effects of desiccation on survival, metabolism-related enzymes and histological structure of adult red swamp crayfish (Procambarus clarkii)
Yuanyuan WANG, Yongxu CHENG, Chenlu LI, Mingming LIU, Yewen XI, Chuanzhong ZHU, Jiayao LI
 doi: 10.12131/20210092
[Abstract](102) [FullText HTML](16) [PDF 1929KB](9)
To investigate the effects of desiccation on adult red swamp crayfish (Procambarus clarkii), we designed a desiccation stress for crayfish for 0, 3, 6, 12, 24, 36, 48, 60, 72, 96, 132 and 144 h under the conditions of (16±1) ℃ and (55±5) % relative humidity (RH). The results show that the half-lethal time (LT50) of male and female crayfish were 148.36 and 144.01 h, respectively. The mass consumption rate increased gradually with the extension of desiccation time; the weight consumption of male reached 16.09% of body mass after 144 h desiccation, while that of female reached 15.87% of body mass after 132 h desiccation. Besides, the histological structure damage of gill, hepatopancreas and muscle was gradually aggravated. Moreover, the activity of lactate dehydrogenase (LDH) in hepatopancreas and muscle first increased and then decreased. The maximum LDH activities of hepatopancreas in female and male were observed at 24th and 36th hour, while those of muscle in female and male were observed at 36th and 48th hour, respectively. The lactic acid (LA) content of muscle showed similar trend, with LA contents of female and male being the highest after 60 and 48 h desiccation stress, respectively. The succinate dehydrogenase (SDH) activity reduced significantly during desiccating. Furthermore, the desiccation tolerance of adult crayfish reached the limit after 48 h, and the respiratory metabolism gradually transformed from aerobic respiration to anaerobic respiration, accompanied by histological damage. In conclusion, the ability of resist desiccation between male and female is different. Thus, the desiccation time should not exceed 36 h when transporting adult crayfishes.
Protective effect of hydrolyzed ultrafiltration fractions from oyster (Crassostrea hongkongensis) on oxidative damage of TM4 Sertoli cells
Xueyan ZHANG, Xiaoming QIN, Haisheng LIN, Wenhong CAO, Huina ZHENG, Jialong GAO, Chaohua ZHANG
 doi: 10.12131/20210071
[Abstract](130) [FullText HTML](12) [PDF 28799KB](10)
In this study, TM4 Sertoli cells were injured by triptolide (TP) to construct a germ cell injury model, so as to explore the protective effect of oyster (Crassostrea hongkongensis) hydrolyzed ultrafiltration fractions on TP-induced oxidative damage of TM4 Sertoli cells in mice (Mus musculus). Besides, the molecular mass distribution and trace metal element content of the oyster hydrolyzed ultrafiltration fractions were detected, and the cell viability, GSH content, MDA content and ROS level of TM4 cells induced by TP by ultrafiltration fractions were compared. The results show that the oyster hydrolyzed ultrafiltration fractions are rich in trace metal elements such as copper, zinc, manganese and selenium; most small molecules and macromolecular substances were separated by ultrafiltration; compared with the model group, ultrafiltration fractions improved the cell viability of TM4 cells induced by TP. The cell viability of <3, 3–5 and 5–10 ku ultrafiltration fractions was higher than that of >10 ku ultrafiltration fraction; <3 ku ultrafiltration fraction could prevent TP-induced oxidative stress damage in TM4 cells, reduce the production of intracellular reactive oxygen species and lipid peroxidation, and enhance the antioxidant activity of TM4 cells.
Study on relationship between body length and blood index of juvenile yellowfin tuna (Thunnus albacores)
Shengjie ZHOU, Rui YANG, Gang YU, Zhenhua MA
 doi: 10.12131/20210052
[Abstract](102) [FullText HTML](21) [PDF 899KB](7)
In order to accumulate the basic physiological index data for juvenile yellowfin tuna (Thunnus albacores), we evaluated the blood potassium ion (K+), calcium ion (Ca2+), chloride ion (Cl), hydrogen ion (H+), pH, glucose, lactic acid, sodium ion (Na+) and total hemoglobin concentration and hematocrit, osmotic pressure of the juveniles of different body lengths (20G: 20−30 cm, 30G: 30−40 cm, 40G: 40−50 cm). Results indicate that the blood parameters of the juveniles were relatively stable in the three body length groups. K+, Ca2+, Cl, H+, pH, glucose and hematocrit were not significantly different between groups (P>0.05). The content of lactic acid and total hemoglobin concentration in the 20G group was significantly higher than the other two groups (P<0.05). The standardized calcium ion in the 30G group was significantly higher than the other two groups (P<0.05). The sodium ion content decreased with the increase of body length gradually, and the difference between the adjacent two groups was not significant (P>0.05). The results show that the juveniles had a small difference between the 30G and 40G groups. The 20G group was relatively different from the other two groups. As body length increased, blood indicators tended to be more stable.
Effect evaluation of alizarin complexone marking for otoliths of juvenile black carp (Mylopharyngodon piceus)
Yahua ZHU, Tao JIANG, Xiubao CHEN, Hongbo LIU, Jian YANG
 doi: 10.12131/20210048
[Abstract](82) [FullText HTML](15) [PDF 1023KB](6)
Investigation on artificial marking technology is very important supporting work for national fish mark release recapture and effectiveness tracing evaluation issues. In this study, two-month old juvenile black carps (Mylopharyngodon piceus) had been immersed in alizarin complexone (ALC) at a concentration of 100 mg·L−1 for 48 h, and then transferred to normal water for 20 d. Three pairs of otoliths (i.e., sagitta, lapillus and asteriscus) were removed from the black carps by continuous sampling, observed under fluorescence microscope and photographed, so as to evaluate the characteristics of deposition and the marking effect of ALC in different otoliths. The results show that the marked areas were clearly observed in each otolith pair under visible light and different excitation light, with a 100% mark success rate. After 20 d of recovery culture in normal water without ALC, the intensity of ALC mark in otoliths of the marked fish was still very high, showing a good marking effect. Moreover, the optimum light source was blue excitation light, followed by green excitation light. The lapillus was the optimal otolith type for ALC marking and for judgment of time lag among the three pairs of otoliths, followed by asteriscus. In addition, there was a time lag of 1 day between the carps immersed in ALC solution and ALC deposition into otolith, as well as between removing immersed carps from ALC solution and disappearance of ALC mark from otolith.
Study on carbonate alkalinity tolerance of Nile tilapia (Oreochromis niloticus)
Yanling WANG, Yan ZHAO, Ming CHEN, Yusong SHI, Jun XU, Shuaishuai LI, Shoujie TANG, Jinliang ZHAO
 doi: 10.12131/20210043
[Abstract](157) [FullText HTML](25) [PDF 1058KB](20)
In this study, we examined the tolerance to carbonate alkalinity of two sizes of Nile tilapia (Oreochromis niloticus) [Large: (21.56±0.27) g, Small: (5.92±0.03) g]. Different carbonate-alkalinity solutions were prepared with NaHCO3 to carry out the experiment: 1) The fish were directly transferred from fresh water to 30 or 22 g·L−1 carbonate alkalinity solutions to determine the mortality. 2) The fish were acutely exposed to different carbonate alkalinity solutions ranging from 6 to 10 g·L−1 for 96 h. 3) For chronic alkaline acclimation experiments, the carbonate concentrations increased gradually at three levels of +2, +4 and +6 g·(L·d)−1. The results show that the half lethal alkalinities of Nile tilapia under acute stress for 96 h ranged from 6.25 to 9.01 g·L−1. The alkaline tolerance of Nile tilapia was weaker than that of fish which adapt to extreme alkaline environment (e.g. Gymnocyprinus przewalskii), but it was still stronger than that of most freshwater cultured fish. At juvenile stage, the tolerance of Nile tilapia to carbonate stress was significantly enhanced when its body mass increased more than three times. Nile tilapia can be acclimated by daily alkaline increment of 2 g·L−1. The relationship of "time-alkalinity-mortality" under acute alkaline stress can be well fitted by complementary log-log model.
Study on relationship between albacore catch rate and water depth and temperature in South Indian Ocean
Xiaoyan XIE, Jintao WANG, Xinjun CHEN, Pimao CHEN
 doi: 10.12131/20210018
[Abstract](172) [FullText HTML](39) [PDF 1292KB](20)
Longline tuna fisheries in the Indian Ocean are commerically important for Chinese offshore fisheries. Water temperature at different depths can affect longline albacore catch rates. In this paper, the generalized additive model (GAM) was used to analyze the relationship between the the catch rate of albacore (Thunnus alalunga) and water temperature at different depths based on the fishery data and corresponding Argo buoy data during 2008−2017. The results show that the catch rate of albacore tuna catch rate was significantly affected by the sea surface temperature (0 m), water temperature at depth of 200 and 400 m. The optimal GAM model explained the variance of catch rate (Catch per unit effort) by 53.3%, and the determining coefficient of model was 0.527. The catch rates of albacore tuna had a nonlinear relationship with the temperature of the three selected water layers. High catch areas were concentrated at the surface layer of 17−30 ℃, 200 m deep sea area of 17−20 ℃, and 400 m deep sea area of 9−15 ℃, and their intersection areas. We have derived the relationship between the spatial distribution of albacore tuna catch rate in the South Indian Ocean and the temperature of three water depth sections for the first time, and the results provide technical support for guiding the rational production of albacore tuna in the Indian Ocean.
Isolation and identification of vibrio resistant photosynthetic bacteria and degradation of nitrite nitrogen and ammonia nitrogen
Yuting WANG, Rongxiang ZHOU, Jihong LI, Yao ZHANG, Tingting ZHOU, Wencai CHEN, Yun PENG, Manli TANG, Guizhen MA, Jianhe XU
 doi: 10.12131/20210016
[Abstract](194) [FullText HTML](57) [PDF 1354KB](11)
In this study, photosynthetic bacteria (PSB) were isolated and purified from marine environmental samples from different areas by double-layer plate coating method and scribing method. Vibrio parahaemolyticus, V. vulnificus and V. anguillarum were used as control. The inhibition of marine photosynthetic bacteria was determined by Oxford cup method, and the degradation of nitrite nitrogen (NO2 -N) and ammonia nitrogen (NH4 +-N) by different strains was determined by naphthalene ethylenediamine hydrochloride spectrophotometry and indophenol blue spectrophotometry. The results show that three strains of photosynthetic bacteria were isolated from 30 sea water and mud samples, and the P-3 strain isolated from the seawater samples of Cheniushan Island in Lianyungang had strong inhibitory effect on three kinds of Vibrio, especially for V. anguillarum, with the inhibition zone diameter of 5.3 mm. The results show that all the three photosynthetic bacteria have certain ability to degrade NO2 -N and NH4 +-N, and P-3 strain had the strongest ability. The degradation rates of P-3 strain were 89.68% and 94.98% respectively, when being cultured in the medium containing 50 mg·L−1 NH4 +-N and NO2 -N for 4 d. P-3 strain was identified as Rhodopseudomonas palustris by morphological observation, physiological and biochemical tests and 16S rDNA sequence analysis.
Effects of salinity and Na+/K+ ratio on survival and histological structure of Litopenaeus vannamei
Jiaqi SU, Huaping ZHU, Changbo ZHU, Bo ZHANG, Ting LI, Suwen CHEN
 doi: 10.12131/20210011
[Abstract](50) [FullText HTML](22) [PDF 958KB](14)
By using method of experimental ecology, we studied the effects of salinity (2, 4, 8, 12, 16) and Na+/K+ (27, 50, 75, 100, 125 and 150) ratio on 72 h survival rate, hepatopancreas and muscle structure of Litopenaeus vannamei juveniles with body mass of (1.35 ± 0.37) g under experimental condition. The results show that survival rate of L. vannamei decreased with increasing salinity when the Na+/K+ ratio was above 75. In addition, when the water salinity was over 8, the survival rate increased with decreasing Na+/K+ ratio. The survival rate of L. vannamei was above 66.67% when the Na+/K+ ratio was 27−75. When the Na+/K+ ratio was 100, the half lethal time (LT50) of L. vannamei was 69.78 and 60.15 h at salinity of 12 and 16, respectively. When the Na+/K+ ratio was 125, the LT50 at salinity of 8, 12 and 16 was 76.23, 62.61 and 49.10 h, respectively. When the Na+/K+ ratio was 150, the LT50 at salinity of 4, 8, 12 and 16 was 87.24, 68.65, 59.4 and 39.95 h, respectively. Based on the two-factor variance analysis, the 72 h survival rate of L. vannamei was significantly influenced by salinity, Na+/K+ ratio and their interactions (P<0.001). Histopathology observation reveals that high Na+/K+ ratio can cause abnormal histological change in shrimp muscle and hepatopancreas, such as cell vacuolation or autolysis, larger intercellular space, fuzzy and disordered boundary between tissues. In general, potassium deficiency can aggravate the tissue injury of L. vannamei with higher salinity.
Effects of water temperature, photoperiod and light intensity on survival, feeding and growth of Schizothorax biddulphi juveniles and their tolerance of salinity and alkalinity
Nianhua ZHAO, He ZHAO, Zhuang QIANG, Zhulan NIE, Jie WEI, JianZhong SHEN
 doi: 10.12131/20210001
[Abstract](118) [FullText HTML](22) [PDF 17074KB](8)
In this paper, we investigated the effects of water temperature, photoperiod and light intensity on the survival, feeding and growth of Schizothorax biddulphi juveniles by using experimental ecological methods; predicted the optimal growth conditions for the juveniles by Box-Benhnken design; and studied the saline alkali tolerance of juveniles by single factor static toxicity acute test. The results show that the survival rate of the juveniles was above 85% at 5−25 ℃. The feeding rate, length growth rate and specific growth rate reached the maximum values at 20 ℃. When the photoperiod was 16 L∶8 D and the light intensity was 500 lx, all the indices of the juveniles reached the maximum values. Under conditions of water temperature of 12.98 ℃, daily light time of 15.07 h and light intensity of 670.27 lx, the best survival, feeding and growth were obtained. The LC50 of NaCl salinity was 4.01, 3.62, 3.29 and 2.92 g·L−1 at 24, 48, 72 and 96 h, respectively, and the safety concentration (SC) was 0.89 g·L−1. The LC50 of NaHCO3 alkalinity was 97.14, 86.75, 80.26 and 74.52 mmol·L−1 at 24, 48, 72 and 96 h, respectively, and the SC was 20.75 mmol·L−1.
Comparison of growth and morphological characteristics of inbred and hybrid families of Micropterus salmoides from Foshan and Taiwan populations
Jiangtao LI, Kaiyu YANG, Xiaotong QIU, Junchao FANG, Feifei HUANG, Xiaolong QIU, Xiaojing LYU, Rishen LIANG, Qingqing LI, Li LIN
 doi: 10.12131/20200262
[Abstract](114) [FullText HTML](20) [PDF 853KB](12)
Taking Foshan and Taiwan populations of Micropterus salmoides as parents, we established four populations including Foshan inbreeding group (Foshan ♀×Foshan ♂), Taiwan inbreeding group (Taiwan ♀×Taiwan ♂), normal progeny (Foshan ♀×Taiwan ♂) and reciprocal progeny (Taiwan ♀×Foshan ♂), in order to compare their growth and morphological characteristics after six-month culture. Results show that the growth performance and coefficient of variation for body mass were significantly higher in the hybid groups than in the two inbred groups. The results of morphological analysis show that the morphological differences of the four populations were mainly in the middle part of trunk and tail. The contribution rate of the first three principal components was 92.9%, and that of the first principal component was 71.3%, mainly reflecting the morphological characteristics of the front and middle part of the body. The contribution rate of the second principal component was 16.6%, reflecting the characteristics of the tail region of fish body. In the scatter plot of the scores of the first two principal components, the four populations could be completely distinguished due to the low overlap area. The stepwise discriminant model constructed by combining measurable traits and frame traits showed the highest accuracy (86.7%–96.0%). The results provide references for the growth and morphological identification of hybrid families of M. salmoides from Foshan and Taiwan populations.
Effects of feeding Candida ethanolica GXU01 on growth, immunity and intestinal flora of tilapia
Qingzhao LIAO, Fuyan CHEN, Ya QIN, Chanchan HUANG, Luodong HUANG, Peihong SHEN
 doi: 10.12131/20200258
[Abstract](144) [FullText HTML](48) [PDF 1153KB](14)
To explore the probiotic potential of Candida ethanolica GXU01 in tilapia culture and to find ecological and friendly feeding bacteria for tilapia sustainable cultivation, we used C. ethanolica GXU01 as feed-additive to feed tilapia. Then we determined the growth performance, intestinal digestive enzymes, serum non-specific immune indexes and intestinal microbial community structure, and challenged the tilapia with Streptococcus agalactiae, so as to comprehensively evaluate the effects of C. ethanolica GXU01 on the growth and immunity of tilapia. The results show that the growth performance, digestive enzyme activity, serum lysozyme activity and complement C3 content of tilapia could be significantly improved by feeding C. ethanolica GXU01 (P<0.05). The abundance of Fusobacteria, Cetobacterium and Akkermansia in the intestinal tract of tilapia increased significantly and those of Cyanobacteria decreased significantly after feed of C. ethanolica GXU01. In the challenge test, the survival rate of tilapia fed with diet containing C. ethanolica GXU01 increased by 26.66%. The study shows that C. ethanolica GXU01 promotes the intestinal digestive ability and immune resistance of tilapia.
Correlation analysis of light intensity and growth, photosynthetic pigment, color value of Betaphycus gelatinae
Lihao TONG, Xiangyu WU, Liangfu HUANG, Jun ZENG, Yaohua SHI, Xianming TANG
 doi: 10.12131/20200256
[Abstract](151) [FullText HTML](17) [PDF 3086KB](5)
We investigated the growth, photosynthetic pigment and color change of Betaphycus gelatinae at different light intensities (1 000, 3 000, 5 000, 7 000 and 9 000 lx). Based on CSE-1 imaging chromaticity detection and analysis, we studied the correlation of color parameter L*a*b*(CIE 1976) with light intensity, growth and photosynthetic pigment. The results show that the relative growth rate and weight gain rate increased significantly with the increase of light intensity. The suitable light intensity for growth was 7 000−9000 lx. However, when the light intensity was 1 000 lx, there was no obvious growth of B. gelatinae. With the increase of light intensity, the contents of chlorophyll a, carotenoids, phycoerythrin and phycocyanin generally decreased, and the color of B. gelatinae gradually changed from reddish brown to green. The tristimulus values (XYZ) showed a significant distribution difference on the CIE 1931 chromaticity diagram at different light intensities. Light intensity was significantly positively correlated with lightness L*(P<0.05), but significantly negatively correlated with red-green value a*(P<0.01). There was a significant positive correlation between relative growth rate with lightness L* and yellow-blue value b*(P<0.05). Chlorophyll a was significantly negatively correlated with lightness L*(P<0.05), but significantly positively correlated with red-green value a*(P<0.05). Both phycoerythrin and phycocyanin were significantly positively correlated with the red-green value a*(P<0.05).
Effects of dietary taurine supplementation in low fish meal feed on growth, digestibility, intestinal enzyme activities of rice field eel (Monopterus albus)
Xiaoli CAO, Zhaolin LI, Yi HU
 doi: 10.12131/20200255
[Abstract](107) [FullText HTML](27) [PDF 645KB](17)
In this study, the healthy rice field eels (Monopterus albus) with body mass of (25.03±0.02) g had been cultured for 10 weeks, and the effects of taurine on the growth, digestibility and intestinal enzyme activity of M. albus were studied. Four treatment groups with high-content fish meal (42%, FM), low-content fish meal (22%, T0) and low-content fish meal diet supplemented with 0.2% (T0.2) and 0.5% (T0.5) taurine were set up, with five replicates in each group. The results show that compared with FM group, the weight gain rate, protein efficiency ratio, dry matter digestibility and protein digestibility of rice field eels decreased in T0 group significantly (P<0.05), while the feed conversion ratio increased significantly (P<0.05). Adding an appropriate amount of taurine could increase the weight gain rate, protein efficiency ratio and dry matter digestibility of rice field eels, but reduce the feed coefficient (P<0.05). The weight gain rate, protein efficiency ratio and protein digestibility in T0.5 group were approximate the same in T0 group (P>0.05). Moreover, comparing with FM group, the intestinal creatine kinase, Na+-K+-ATPase, alkaline phosphatase, trypsin and lipase activities in T0 group decreased significantly (P<0.05), but the activities of the aforementioned intestinal enzyme in T0.2 group increased significantly (P<0.05). The activities of Na+-K+-ATPase, alkaline phosphatase, trypsin and lipase in T0.5 group were higher than those in T0 group, without significant difference (P>0.05). To sum up, 0.2% taurine supplementation in low-content fish meal feed can improve the growth performance, intestinal digestion and absorption function of rice field eel, but excess taurine (0.5%) has no obvious effect.
Effects of temperature and initial cell density ratio on growth and competition between Navicula pelliculosa and Chlorella vulgaris
Xiaoli LI, Ling TAO, Lili DAI, Liang PENG, Gu LI
 doi: 10.12131/20200250
[Abstract](104) [FullText HTML](33) [PDF 973KB](8)
In order to make use of interspecific competition to co-culture beneficial microalgae and build excellent algal forms in ponds, we designed different temperature gradients (10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃ and 35 ℃) and different initial density ratios (Navicula pelliculosaChlorella vulgaris was 1∶10, 1∶1, 1∶0.1, respectively) for an experiment, to investigate the effects of temperature and initial density ratios of N. pelliculosa and C. vulgaris on their growth and competition. The results show that the cell density of N. pelliculosa in mono-culture group increased first and then decreased at 10−15 ℃, and increased gradually at 20−30 ℃ with a maximum value of 0.50×106 cells∙mL−1; 25−30 ℃ was the optimal growth temperature for N. pelliculosa which could not survive at 35 ℃. C. vulgaris grew slowly or even stopped at 10−15 ℃, and grew rapidly at 20−35 ℃ in mono-culture group. The maximum value of the cell density was 14.15×106 cells∙mL−1. The optimal growth temperature was 35 ℃. The growth rate of N. pelliculosa in mixed culture group was higher than that in mono-culture group, and increased gradually with increase of proportion of C. vulgaris. The maximum cell density of N. pelliculosa in mixed culture group was significantly higher than that in mono-culture group. The smaller the initial cell density was, the faster C. vulgaris grew in mixed culture group. The growth rate of 1∶0.1 group was significantly higher than that in mono-culture group, and the growth rate of 1∶10 group was significantly lower than that in mono-culture group. The competitive inhibition parameter data show that C. vulgaris had little competitive inhibition on N. pelliculosa, and the competitive inhibition parameter of C.vulgaris against N. pelliculosa (α value) increased with increase of temperature and proportion of C. vulgaris, while the competitive inhibition parameter of N. pelliculosa against C. vulgaris (β value) increased with increase of temperature and proportion of N. pelliculosa. The two microalgae can coexist peacefully.
Biological characteristics of Ctenopharyngodon idellus in middle and lower reaches of Pearl River
Yujie HE, Shuli ZHU, Zhi WU, Xinhui LI, Jie LI
 doi: 10.12131/20200242
[Abstract](160) [FullText HTML](36) [PDF 1426KB](15)
In order to find out the current status of the population structure and growth characteristics of grass carp (Ctenopharyngodon idellus) in the middle and lower reaches of the Pearl River, we have investigated the grass carp population from 2019 to 2020. The results show that the body length of grass carp was 103−665 mm [average: (347.89±96.73) mm]. The body mass was 21.4−6 650.0 g [average: (986.87±842.96) g]. The population age was of 0+−5+, and the dominant age was 1+−3+, accounting for 92.8% of the total number of samples. The body length had a significant power function relation with body mass for uniform motion pattern. The growth could be described by Von Bertalanffy equation with the growth parameters: L=1187 mm, k=0.128, t0=−0.282, W=31 344.51 g. The index of length growth performance (φ) of grass carp was 5.26, and the growth inflection age was 8.29. The total mortality rate, natural mortality rate, fishing mortality rate and exploitation rate were 0.58, 0.29, 0.29 and 0.5, respectively. The sex ratio (Females/Males) was 1.07: 1. The sexual maturation was mainly at Stage II. Compared with the previous data, the growth performance and fecundity of grass carp all showed a decline tendency; the population structure tended to be miniaturized. In order to promote the recovery of grass carp resources in the middle and lower reaches of the Pearl River, it is recommended to reduce the fishing intensity. Besides, the catch body length should be greater than 791 mm and the mass should be greater than 9 279.11 g.
Effects of water temperature, salinity and pH on embryonic development of Selenotoca multifasciata
Yanqiu SUN, Jianyi LIU, Ping ZHUANG, Qi LI, Xiong ZOU, Guangpeng FENG, Feng ZHAO, Yanfang YU, Xuena SUN, Jun YANG, Yu WANG, Xiaorong HUANG
 doi: 10.12131/20210109
[Abstract](82) [FullText HTML](20) [PDF 1129KB](28)
The characteristics of embryonic development of Selenotoca multifasciata under different temperature, salinity and pH were studied for the first time, to provide a reference for the selection and regulation of suitable conditions for seedling cultivation of S. multifasciata. The embryos of S. multifasciata were incubated at different temperatures (16, 20, 24, 26, 28, 30, 32, 34, 36 °C), salinities (fresh water, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50) and pH (5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0). The results indicate that the hatching temperature of S. multifasciata was 24–36 °C at salinity of 32. With the increase of temperature, the hatching time descreased, and the hatching rate first increased and then decreased, while the deformity rate was on the contrary. The optimal hatching temperature was 26–28 ℃. At pH of 5.5–8.5, the hatching time descreased with the increase of pH. The hatching rate first increased and then decreased, while the deformity rate was on the contrary. The optimal hatching pH was 7.5–8.2. The larvae hatched out at salinity of 5–50. The hatching rate first increased and then decreased with the increase of salinity, while the deformity rate was on the contrary. The optimal hatching salinity was 25–29.
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Special Issue: 2020 Youth Academic Seminar of Sea Area Research Institutes of Chinese Academy of Fishery Sciences  

Cover & Content
2021, 17(4): 1-4.  
[Abstract](19) [FullText HTML](10) [PDF 2150KB](895)
Research Paper
Habitat traits of Lateolabrax japonicus in different subhabitats of Yangtze River Estuary
PENG Biaobiao, ZHAO Feng, WANG Sikai, ZHANG Tao, YANG Gang, MIAO Zhongbo, ZHUANG Ping
2021, 17(4): 1-8.   doi: 10.12131/20210023
[Abstract](282) [FullText HTML](66) [PDF 1096KB](32)
In order to explore the selection and utilization of Chinese seabass (Lateolabrax maculatus) in different subhabitats of the salt marsh of the Yangtze River Estuary, we investigated three subhabitats of tidal creek, mudflat and Scirpus mariqueter vegetation area, and took samples in spring, summer, autumn and winter. The results show that L. maculatus was the dominant species in that area. The spatial niche breadth of L. maculatus decreased gradually in spring, summer and autumn, while the temporal niche breadth was in a descending order of tidal creek>S. mariqueter vegetation area>mudflat. There was a significant spatial-temporal difference in the population distribution of L. maculatus (highest in spring but lowest in autumn; most in tidal creek, followed by S. mariqueter vegetation area and mudflat). The majority of L. maculatus entering the Yangtze River Estuary were juveniles, which occurred mainly in spring. Small-size individuals preferred to inhabit in tidal creek, while large-size ones preferred to inhabit in mudflat and S. mariqueter vegetation area. For the average feeding grade of L. maculatus, it increased gradually from spring to winter in tidal creek, and increased gradually from spring to autumn but decreased sharply in winter in mudflat, reaching the maximum in summer and decreased gradually in autumn and winter in S. mariqueter vegetation area. In spring, summer and autumn, the average feeding grade of L. maculatus was in a descending order of S. mariqueter>tidal creek>mudflat. However, it was in a descending order of tidal creek>S. mariqueter> mudflat in winter.
Community structure characteristics of zooplankton in main freshwater rivers of Jiangmen City, Guangdong Province
WANG Teng, LIU Yong, QUAN Qiumei, LIN Lin, XIAO Yayuan, LI Chunhou, LI Hong
2021, 17(4): 9-17.   doi: 10.12131/20210019
[Abstract](153) [FullText HTML](42) [PDF 1016KB](21)
In order to understand the community structure of zooplankton in the main freshwater rivers of Jiangmen, Guangdong Province, we investigated the zooplankton community structure in Tanjiang River, Yinzhou Lake and Xijiang River from December 2016 to October 2017. Altogether 157 species of zooplankton had been observed, including 74 species of rotifers, 43 species of protozoa, 21 species of cladocers and 19 species of copepods. The annual average density and biomass of zooplankton were 1 651 and 0.80 mg·L−1, respectively. The density of protozoa was the highest (1 164 ind·L−1). And the highest biomass of rotifers and copepods was 0.37 and 0.31 mg·L−1, respectively. Compared with the historical level, the species number of large zooplankton had decreased significantly, while the small zooplankton had increased significantly. And the density of zooplankton increased significantly, while their biomass decreased significantly. The Shannon-Wiener diversity index H' was 1.05−4.36, and the Pielou index J' was 0.23−1.15. There were 30 dominant species in the survey area, and the number of protozoa was the largest (15 species). Among the dominant species, 10 were eutrophic indicator species, all of which were rotifers. Dominant species of the indicator species for eutrophic water were only distributed in Tanjiang River and Yinzhou Lake, indicating that Xijiang River water quality is the best.
Effects of environmental factors and external stimulus on immune indexes of Crassostrea hongkongensis
WANG Jiawen, LU Jie, YAO Tuo, YE Lingtong, WANG Jiangyong
2021, 17(4): 18-26.   doi: 10.12131/20210051
[Abstract](178) [FullText HTML](34) [PDF 925KB](22)
Disease problems have seriously threatened the development of Crassostrea hongkongensis aquaculture. Thus, finding suitable biomarkers for C. hongkongensis health assessment is important for preventing C. hongkongensis diseases. We investigated the effects of salinity stress, ammonia stress, immune stimulation and air exposure stress on the immune indexes of C. hongkongensis. The results show that the CAT activity increased significantly under both low-salt (Salinity 3) and high-salinity (Salinity 30) stress (P<0.05). High-salt stress also increased SOD and NOS activities significantly (P<0.05). The stress of high concentration of ammonia nitrogen (60 mg∙L–1) caused a significant decrease in the CAT activity (P<0.05), while the activities of ACP and SOD increased significantly under both high and low concentration of ammonia nitrogen (6 mg∙L–1) stress (P<0.05). Both Vibrio harveyi and lipopolysaccharide stimulation inhibited the CAT activity significantly (P<0.05). In addition, the CAT activity during air-exposure stress at 4 and 25 ℃ showed a significant decreasing trend (P<0.05). Therefore, CAT is more sensitive to environmental changes than other immunological indicators, which may be a health-related evaluation index of C. hongkongensis.
Effects of sex steroid hormones (estradiol and testosterone) on growth traits of female, male and pseduo-male Chinese tongue sole (Cynoglossus semilaevis)
WANG Jialin, YANG Yingming, YANG Qian, WANG Na, CHEN Songlin
2021, 17(4): 27-34.   doi: 10.12131/20210030
[Abstract](116) [FullText HTML](36) [PDF 1038KB](19)
A variety of fish, including Chinese tongue sole (Cynoglossus semilaevis), have sexual size dimorphism, and this growth dimorphism may be related to the interaction of sex steroid hormones and growth axis-related genes. For the early stage of this study, transcriptomics analysis has found that sex steroid hormones might be involved in the growth regulation of Chinese tongue sole. In order to explore the effect of sex steroid hormones on the growth difference of different sexes of Chinese tongue sole, we injected 16-month-old female, male and pseudo-male fish with estradiol and testosterone hormones, and measured the growth hormone 1 (gh1), insulin-like growth factor 1 (igf1) and suppressor of cytokine signaling 3 (socs3) for quantitative analysis. The results reveal that the two sex steroid hormones had inhibitory effects on the growth performance of individuals of different sexes of Chinese tongue sole. After the treatment, the expressions of gh1 and igf1 in the brain and liver showed an overall downward trend, and the expression of socs3 in the muscle and liver increased significantly, indicating that the growth performance of fish had declined. By exploring the effects of sex steroid hormones on the growth performance of different sexes of Chinese tongue sole, we provide references for the in-depth study of sex steroid hormones in the regulation of fish sex size abnormalities.
Dietary composition and trophic position of Tachypleus tridentatus
GUO Qingyang, GU Yangguang, BAO Yuyuan, LI Yinkang, ZHOU Chuanjiang, XIE Xiaoyong
2021, 17(4): 35-40.   doi: 10.12131/20200234
[Abstract](216) [FullText HTML](49) [PDF 702KB](40)
The stable isotope ratios (δ13C and δ15N) of carbon and nitrogen of Tachypleus tridentatus collected from Beibu Gulf and its potential food source species (Shrimps, crabs, bivalves and fishes) in food web were determined. Besides, their food composition and nutritional position were anayzed by stable isoelement mixture model (SIAR). The results show that the average δ13C and δ15N values of the T. tridentatus were (−17.11±0.03)‰ and (12.14±0.20)‰, respectively. Potential food sources of T. tridentatus were shrimps, crabs, bivalves and fishes. The SIAR model shows that bivalves were the main food source of T. tridentatus with average contribution rate of 31.27% (Fishes: 25.91%, crabs: 23.50%, shrimps: 19.32%). The trophic position of T. tridentatus was 2.02±0.06, while those of fishes, shrimps and crabs were 2.13±0.51, 2.36±0.09 and 2.61±0.21, respectively. Trophic position analysis shows that T. tridentatus is in a relatively weak position in the natural ecosystem food web, and scientific protection measures are urgently needed as it is already endangered.
Effects of low salinity pressure on biological tissue and immunity enzymes activities of Sipunculus nudus
LI Junwei, HU Ruiping, CHEN Suwen, GUO Yongjian, ZHU Changbo, LI Ting, XIE Xiaoyong, SU Jiaqi
2021, 17(4): 41-48.   doi: 10.12131/20210022
[Abstract](124) [FullText HTML](35) [PDF 1096KB](14)
In order to understand the response of the biological and physiological indicators of Sipunculus nudus to low salinity, we evaluated the effects of low salinity pressure on the survival rate, osmotic pressure, biological tissue and immunity enzymes activities of S. nudus which were cultured for 96 h in water with abrupt salinity drop of 0 (S30), 5 (S25), 10 (S20), 15 (S15), 20 (S10) and 25 (S5). The results show that: 1) S. nudus could tolerate the salinity drop of 10, but would die when the salinity dropped over 15. 2) The coelomic fluid of S. nudus increased with the decrease of water salinity significantly, and there was a significant positive correlation between the body mass and coelomic fluid volumn (R2>0.96). 3) The osmotic pressure and body protein contents decreased with the decrease of water salinity (P<0.05). 4) In the low salinity treatments, the connective tissue of longitudinal and circumferential muscle fibers of the body wall were thin, and the staining of columnar cells was lighter. For the tentacle, its adhesion ability was weaker as the epithelial cells became larger. 5) SOD and CAT activities in the groups of S30 and S25 were relatively stable, while the body SOD and coelomic fluid CAT in the groups of S10 and S15 first decreased and then increased; however, the CAT of coelomic fluid in the groups of S10 and S15 first increased and then decreased. SOD and CAT activities in the coelomic fluid had strong varation. In summary, low salinity pressure can affect the survival rate, osmotic pressure, biological tissue and immunity enzymes activities of S. nudus significantly.
Effects of polysaccharide from Endothelium corneum gigeriae galli on growth, digestive, intestinal antioxidant capacity and serum biochemical indices of Lates calcarifer
ZENG Xiangbing, DONG Hongbiao, WEI Zhengkun, DUAN Yafei, CHEN Jian, ZHANG Hui, SUN Caiyun, XU Xiaodong, ZHANG Jiasong
2021, 17(4): 49-57.   doi: 10.12131/20210028
[Abstract](127) [FullText HTML](19) [PDF 1106KB](21)
To investigate the effects of dietary polysaccharide from Endothelium corneum gigeriae galli (PEGG) supplementation on the growth, digestive, intestinal antioxidant capacity and serum biochemical indices of Lates calcarifer and to provide references for the application of PEGG in healthy culture of L. calcarifer, we had fed juvenile L. calcarifer [Body mass of (11.85±1.66) g] by basal diets with PEGG at 0 (Control group), 5 (Low-dose group), 20 (Medium-dose group) and 80 g·kg−1 (High-dose group) for eight weeks. The results show that compared with the control group, PEGG supplementation groups could: 1) increase the final body mass, weight gain rate and specific growth rate of juvenile L. calcarifer, and the difference was significant in the high-dose group (P<0.05); 2) increase the digestive enzyme activity significantly (P<0.05); 3) improve the histological structure of intestine significantly, indicating that PEGG increased the fold height, fold width and muscular thickness significantly (P<0.05); 4) enhance the antioxidant capacity significantly. The superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) activity, concentration of glutathione (GSH) and total antioxidant capacity (T-AOC) increased in the PEGG supplementation groups, while malondialdehyde (MDA) concentration decreased significantly (P<0.05); 5) improve the serum biochemical indices. Cholesterol in all the treatment groups decreased significantly, while ALT and AST in the medium-dose group decreased significantly (P<0.05). In conclusion, dietary PEGG can improve the digestive capacity, antioxidant capacity and serum biochemical indices of juvenile L. calcarifer, and promote the growth performance. The optimal PEGG supplementation level is 20 g·kg−1.
Preparation and antioxidant properties of Maillard reaction products from Schizochytrium limacinum protein peptides
HU Xiao, LIU Jing, GAO Ying, LI Ruijie, LI Laihao, YANG Xianqing, CHEN Shengjun, WU Yanyan, QI Bo, RONG Hui
2021, 17(4): 58-65.   doi: 10.12131/20210056
[Abstract](148) [FullText HTML](41) [PDF 882KB](15)
The Schizochytrium limacinum hydrolysate (SLH) was prepared from defatted S. limacinum residues, so as to analyze its Maillard reaction conditions. Besides, we explored the antioxidant activities of Maillard reaction products (MRPs) from the isolated fractions of SLH by ultrafiltration and sephadex gel column chromatography. The optimal Maillard reaction parameters were obtained as follows: mass ratio (ribose: peptide) of 1∶1, pH of 9, temperature of 100 ℃ and time of 6 h (the reducing power activity was 1.24 at 5 mg·mL−1 and the DPPH radical scavenging rate was 88.62% at 12.5 mg·mL−1). The SLH was ultra-filtered to obtain the fractions of SLH-1 (<5 kD), SLH-2 (<10 kD) and SLH-3 (<50 kD). It is found that the SLH-1 had the strongest antioxidant capacity before and after Maillard reaction. Then the SLH-1 was further separated by Sephadex G-25 gel column to obtain the fractions of SLH-1-I, SLH-1-II, SLH-1-III and SLH-1-IV. Higher molecular mass fraction of SLH-1-I had higher antioxidant activity after Maillard reaction (the reducing power activity was 0.741 at 2 mg·mL−1 and the DPPH free radical scavenging rate was 79.41% at 5 mg·mL−1). Amino acid composition analysis shows that Maillard reaction could decrease the contents of Tyr, Lys, His, Arg and Trp, etc. However, there was no obvious change in the content of essential amino acids after Maillard reaction.
Influence of main structural parameters on performance of bottom trawl with large-size mesh
WANG Yongjin, ZHANG Xun, ZHANG Yu, ZHOU Aizhong, LI Ziniu, WANG Shuaijie, LIU Longteng, WANG Lumin
2021, 17(4): 66-73.   doi: 10.12131/20210026
[Abstract](96) [FullText HTML](26) [PDF 1278KB](12)
To optimize the structure of bottom trawl with lagre-size mesh, we selected a typical domestic single bottom trawl with large mesh as research object. Based on L9(34) orthogonal table, we designed the orthogonal tests including factors such as the ratio of total length of net to perimeter (L/C), the ratio of headline length to groundline length (S1/S2), and the ratio of net body length to total length of nets (Lb/L). Besides, we applied the mean and extreme difference analysis method to detect the influence of above structure parameters on resistance (R), vertical expansion of trawl mouth (H) and energy consumption coefficient (Ce). The results show that with different horizontal expansion, the influence of three factors on R followed an order of L/C>S1/S2 >Lb/L, that on H followed an order of S1/S2>Lb/L>L/C, and that on Ce followed an order of L/C>S1/S2>Lb/L. The L/C of this type of trawl should be relatively smaller than that of trawl with small-size mesh, and the smaller the L/C was, the smaller R would be. Under these conditions, L/C=0.2 was the optimal value when vertical expansion of bottom trawl and energy consumption coefficient were used as indicators. Compared with small-size mesh trawl, S1/S2 should be higher, and the higher the S1/S2 was, the better the vertical expansion of the net mouth would be. Within the range of 0.83–0.99, S1/S2 had no significant impact on the resistance, and S1/S2=0.99 was the optimal value when energy consumption coefficient was taken as the indicator. Lb/L decreased with the increase of mesh size, but the decreasing range gradually reduced. Lb/L=0.65 should be suitable for medium or low speed trawl, while Lb/L=0.75 should be more suitable for high speed and fastly towing.
A study on settlement performance of falling-net based on GAM
LI Jie, ZHANG Peng, WANG Teng, YAN Lei, YANG Bingzhong, CHEN Zuozhi
2021, 17(4): 74-81.   doi: 10.12131/20210070
[Abstract](149) [FullText HTML](38) [PDF 1195KB](19)
In order to comprehensively understand the settlement performance of falling-net, as well as to provide references for the development of falling-net model test and improvement of fishing gear and method, we conducted sea trials in the central-southern South China Sea in March 2016, and studied the settlement performance of falling-net based on polynomial regression and Generalized Additive Model (GAM). The results show that: 1) Free settlement was a more critical factor affecting the total settlement depth. 2) 90.0–119.9 s was an appropriate free settlement time based on the settlement performance of the falling-net. 3) The free settlement speed first increased in a short time and then decreased, the maximum value occurring at 10th s. The damping settlement speed remained relatively stable in the first 50 s with little change, but then decreased rapidly. 4) Free settlement time (Tf), wind speed (Sw), and direction angle between wind and current (\begin{document}$ \alpha $\end{document}) had significant influences on free settlement depth. Tf, Sw, drift speed of fishing boat (Sb) and \begin{document}$ \alpha $\end{document} had significant influences on damping settlement depth. The study suggests that: 1) The influences of Sw and \begin{document}$ \alpha $\end{document} on free settlement depth and damping settlement depth are complex and non-linear, and may affect the settlement of falling-net through waves and changing the relative position between fishing boat and falling-net. 2) Sb has a significant influence on damping settlement depth. This may be caused by the fact that Sb affects the degree of closure of net-mouth and hauling of purse line.
Frequency domain analysis of hydrodynamic characteristics of mariculture ship with truss and plate frame hybrid structure
WANG Shaomin, YUAN Taiping, YANG Xieqiu, TAO Qiyou, SHEN Wei, HU Yu, HUANG Xiaohua
2021, 17(4): 82-90.   doi: 10.12131/20210021
[Abstract](113) [FullText HTML](59) [PDF 2039KB](20)
In order to study the hydrodynamic performance and motion amplitude response characteristics of the mariculture ship composed of truss structure and several floating bodies with plate and frame structures, we calculated the hydrodynamic characteristics of the ship in frequency domain based on the three-dimensional potential flow theory and Morison equation. Then we obtained and analyzed the hydrodynamic parameters and motion response of the mariculture ship. The results show that the additional mass and radiation damping of the mariculture ship were sensitive to the change of frequency, and the sensitivity was obviously different in the movement of the mariculture ship in different directions, and the additional mass and radiation damping of the three rotations were larger than those of the translations, which were both closely related to the structural shape of the mariculture ship. Under the action of incident waves in every direction, the first-order wave force of the mariculture ship increased at first and then decreased with the increase of frequency, and the first-order wave force curve tended to be stable in the high frequency section under the action of incident waves in different directions. However, there was a big difference in the middle and low section. Under the action of high-frequency and low-frequency excitation, the motion response of the mariculture ship was small, but the resonance occurred when it moved in the medium and short period regular waves. The surging and pitching were the main motion modes when ship was with follow wave or head wave condition, and roll and heave motions were the main motion modes in bean wave.
Research on calculating fishing depth of krill by sonar data
WANG Shuxian, ZHANG Shengmao, DAI Yang, WANG Yongjin, SUI Jianghua, ZHU Wenbin
2021, 17(4): 91-97.   doi: 10.12131/20210020
[Abstract](167) [FullText HTML](53) [PDF 14130KB](15)
In order to determine the trawl depth quickly, improve the fishing efficiency and reduce the cost of fishery production, the paper proposes a method for calculating the optimal fishing depth of the specified fish target based on the sonar device metadata. Sonar device metadata structure is relatively complex and contains much redundant data. In the paper, the original data were simplified, and the information of seabed depth and target strength was calculated and extracted. The effective data range and noise data range were determined according to the type of target fishery resources. After filtering the noise data, the effective data was displayed in the form of statistical chart. The target fishery resources of each depth were counted. The relationship between depth and target fishery resources was constructed, and the optimal fishing depth was calculated and predicted by various methods. The results show that the optimal fishing depth of krill (Euphausia superba, target intensity −69.5–−40.8 dB) was 172.9–187 m in the survey area. According to the sonar data obtained in a certain sea area over a period of time, the optimal fishing depth of the target fishery resources in that sea area can be calculated quickly.
Effects of mooring pattern on dynamic characteristics of a deep-water aquaculture cage
SUI Liuyang, HUANG Xiaohua, LIU Haiyang, HU Yu, YUAN Taiping, WANG Shaomin, TAO Qiyou
2021, 17(4): 98-108.   doi: 10.12131/20210049
[Abstract](125) [FullText HTML](41) [PDF 2141KB](24)
We established a numerical model for calculating the dynamic characteristics of a triangular high-density polyethylene (HDPE) deep-water aquaculture cage in waves and current based on the Finite Element Method. To verify the accuracy of the numerical model, we carried out a series of physical model tests on the single-point mooring (SPM) cage under the conditions of pure wave and combined wave-current, in which the model scale was set at 1∶15. The relative error between the numerical and experimental results was within 10%. Afterwards, considering the sea state of the prototype cage, the calculated parameters for waves and currents were as follows: wave height 4–6 m, period 9 s, current velocity 0.5–1.5 m·s−1. We analyzed the deformation of the floating collar and the mooring force of the cage with single-point mooring (SPM) and multiple-point mooring (MPM). Besides, we discussed the effect of the mooring pattern on the motion characteristics of the cage. The results show that under the conditions of wave and current, the peak value of MPM force was higher than that of SPM force, and the difference became greater with the increase of velocity and wave height. Under the condition of severe waves and strong currents, the MPM system could reduce the deformation of the floating collar. However, the mooring pattern had little influence on the heave of the cage collar. For the MPM system, the x-axis displacement of the collar was greater than that of the SPM system, in which the difference was 25.64%. During a wave period, the xz plane profiles of the net deformation under sea conditions were almost the same for the two different mooring systems.
Research on performance of cavitation jet equipment for deep-water cage cleaning
YUAN Taiping, HU Yu, WANG Shaoming, LIAO Yuqi, TAO Qiyou, HUANG Xiaohua, LIU Haiyang, GUO Gengxi
2021, 17(4): 109-117.   doi: 10.12131/20210027
[Abstract](176) [FullText HTML](48) [PDF 2976KB](12)
To study the cleaning mechanism and influence factors affecting of fouling organisms attached to cage net, we applied numerical simulation method and prototype testing to investigate the biofouling removal rate of cleaning equipment with different inlet pressures and nozzle diameters, and then explored the biofouling removal mechanism of aquaculture net cage under the action of cavitation jet. The numerical simulation results show that the maximum gas volume fraction of nozzle showed an increasing trend when the nozzle diameter was 0.6−1.0 mm under rated flow, and the maximum gas volume fraction value of d=1.0 mm nozzle was 37.5%. The flow velocity of the jet 40 mm away from the nozzle outlet decreased by 85.57%−96.98%, and the velocity of the nozzle decreased significantly in submerged environment. Further water tank cleaning test results show that when the input pressure was 18.8 MPa and the diameter value of nozzle was 0.8 mm, the largest cleaning rate of aquaculture nets of the cleaning equipment was 79.76%. The shellfish fouling organisms mainly fell off in the form of shell breaking under the impact of cavitation jet of cleaning equipment. After the cleaning, most of the residues was the soft foot silk tray of shellfish with strong adsorption. The soil on the surface of the net was completely removed and presented the primary color of the breeding net.
Experimental study on mooring force of a single-point mooring fish cage with ship-type truss structure
WU Yuanjin, HUANG Xiaohua, LIU Haiyang, HU Yu, CHEN Changping, YUAN Taiping, WANG Shaomin, TAO Qiyou
2021, 17(4): 118-125.   doi: 10.12131/20210025
[Abstract](113) [FullText HTML](25) [PDF 1139KB](14)
Safe and efficient large-scale deep-sea aquaculture cage is an important facility leading the development of deep-sea aquaculture. In this study, we tested a single point mooring cage with a ship type truss structure with a 1∶40 wave-current tank model scale, and compared and analyzed the mooring forces of the cage under two different single point mooring modes of normal and failure conditions. On this basis, we studied the effect of netting, wave and current on the mooring force of cage. The results show that compared with the normal condition, the mooring force of the cage under the failure condition increased significantly, having a great impact on the safety of the cage. Under the normal condition, the stress of net cage increased with the increase of wave height, from 12.5 cm to 17.5 cm, and the mooring stress of net cage increased more than tripled. Under the combined action of wave and current, the mooring force of the cage was positively correlated with the velocity but negatively correlated with the period. Compared with the cage without netting, the mooring force with netting increased by more than doubled under the pure wave condition, and increased by 30%–60% under the combined action of wave and current. The results provide theoretical basis and data support for the mooring design and offshore installation of ship truss cages in the future.
Research Notes
Establishment and optimization of micro-reaction system for determination of oyster glycogen content
CHEN Xi, WU Biao, WANG Yan, SUN Xiujun, ZHOU Liqing, LIU Zhihong
2021, 17(4): 126-132.   doi: 10.12131/20210040
[Abstract](102) [FullText HTML](36) [PDF 941KB](16)
In this study, soft tissues of fresh oyster (Crassostrea ariakensis) were used as the experimental material for the determination of glycogen, and the optimal reaction conditions were determined by analyzing the absorbance values obtained with different anthrone sulfuric acid ratios and at different reaction times. Then the lowest detection limit, stability and accuracy of this method were evaluated, and a trace detection system for oyster glycogen was established. The established micro-reaction system had a volume of 300 μL including 200 μL of 0.2% anthrone sulfuric acid solution and 100 μL of sample solution, and the reaction time in boiling water bath was 10 min. The minimum detection limit of glucose was 0.001 5 mg·mL−1 and the coefficient of variation of the standard curve was less than 4%, indicating the high detection sensitivity and good repeatability of the method. In addition, after the reaction completed, absorbance basically remained unchanged within 120 min at room temperature, proving the high stability of this reaction. The recovery rate of glucose from six tissues including oyster mantle, gill, lip, gonad, hepatopancreas and adductor muscle were between 95.3% and 105.8%, indicating that this method has high accuracy. Thus, the established method for the determination of oyster glycogen has high repeatability, stability and accuracy, having the advantages of low reagent consumption, simple operation and low cost per sample. It is suitable for batch determination of glycogen in a large amount of samples. This study provides an effective technical method for quickly and efficiently determining glycogen in oyster samples.
Progress and prospects of infection, prevention and control of norovirus in oyster
ZHAO Feng, TONG Lihui, YANG Min, WANG Shanshan, LIU Nan, SUN Yong, ZHOU Deqing
2021, 17(4): 133-140.   doi: 10.12131/20210042
[Abstract](196) [FullText HTML](61) [PDF 579KB](23)
Norovirus (NoV) is the main pathogen of non-bacterial acute gastroenteritis. Oysters are important carriers for the spread of NoV, which can enrich NoV from contaminated seawater and environment through filter feeding. People tend to eat raw or lightly cooked oysters, which may cause NoV infections. About half of the foodborne diseases associated with oysters are caused by NoV. Reverse transcription fluorescent quantitative PCR (RT-qPCR) is the main method for detecting NoV, but it cannot distinguish infectious from non-infectious viruses effectively. Since NoV cannot be cultured in vitro, RT-qPCR has limitations in assessing the effectiveness of inactivation methods for NoV. Porcine gastric mucin (PGM), propidium monoazide (PMA) and other nucleic acid intercalators combined with RT-qPCR have shown potential applications in the detection of infectious NoV. High hydrostatic pressure treatment is an effective method to reduce norovirus in shellfish, and the pressure of over 400 MPa can inactivate NoV significantly. In this paper, we review the enrichment of NoV in oyster, the detection methods to distinguish infectious NoV and the inactivation of high hydrostatic pressure technology on NoV in Pacific oysters (Crassostrea gigas), pleated oysters (Alectryonella plicatulas) and Kumamoto oysters (C. sikamea), so as to provide references for the establishment of effective NoV risk warning and non-thermal inactivation technology in the future.
Display Method:
Cumulative changes of characteristic substances of off-flavor of grass carp in two culture systems
Li YAN, Kang LI, Gharti Chetri KAMALA, Qiang LU, Yan XU, Rucong LIU, Guixiang WANG, Gadiri Sow ABDOUL, Liping LIU
 doi: 10.12131/20210167
In order to investigate the influence of culture systems on the contamination of off-flavor in the aquaculture water and grass carp (Ctenopharyngodon idella), we studied the accumulation of geosmin (GSM) and 2-methylisoborneol (2-MIB) in the fish in the in-pond raceway system (IPRS) and the traditional culture system. We dynamicaclly detected 2-MIB and GSM contents in the water and fish muscles in different culture systems and applied the Pearson analysis. The results show that the 2-MIB concentration in the water and fish muscle in the IPRS system increased significantly with the extension of aquaculture time. The GSM concentration also showed a gradual accumulation trend, and the changes in the concentrations of the two substances in the muscle remained consistent with those in the water. In the traditional pond system, the concentration of 2-MIB gradually increased without significant difference, and the fish muscle had significantly higher concentration at the end of the experiment than at previous stages. The GSM concentration of both pond water and fish muscle first decreased and then increased. Correlation analysis shows that the accumulation of both GSM and 2-MIB was positively correlated with fish mass and length. In conclusion, the accumulation of off-flavor compounds in pond water and fish muscle is affected by the culture system. Grass carp with body mass between 0.42–1.23 kg accumulates faster.
Epidemiology investigation of Perkinsus spp. in shellfish along coastal area of Guangdong Province
Xiaotong YANG, Lingtong YE, Jie LU, Tuo YAO, Jiangyong WANG, Yaowu FU, Qizhong ZHANG
 doi: 10.12131/20210183
Shellfish are generally cultured in open sea areas, which makes it difficult to carry out shellfish disease prevention and control. Therefore, investigating the epidemic infection law of pathogens is particularly important for the occurrence, development and control of shellfish pathogens. In this paper, we applied common PCR (Polymerase Chain Reaction) technology to investigate the seasonal dynamics and spatio-temporal distribution of Perkinsus spp. among five mainly cultivated shellfish in the six aquaculture locations along the coast of Guangdong Province. Two Perkinsus spp. were detected (P. beihaiensis and P. olseni). The prevalence of P. beihaiensis was significantly higher than that of P. olseni. Among the five sampled shellfish species, except Crassostrea angulate, all of them were detected the infection of Perkinsus spp. C. hongkongensis and Haliotis diversicolor were infected by two Perkinsus spp., while Pinctada martensii and Chlamys nobilis were infected just by P. olseni. The prevalence of Perkinsus spp. in the areas of western Guangdong, including Zhanjiang, Yangjiang, and Jiangmen was 17.17%, significantly higher than that in the areas of eastern Guangdong, including Shanwei, Jieyang, and Shantou. The prevalence of Perkinsus spp. in summer and autumn was 15.67%, significantly higher than that in winter and spring. In different coastal areas, the seasonal occurrence variation of Perkinsus spp. might be affected by the host's culture environment, cultivated mode, feeding type, living type and other comprehensive factors.
Effects of dietary Clostridium butyricum supplementation on growth performance and intestinal flora of juvenile Trachinotus ovatus
Yang WU, Keng YANG, Xiaolin HUANG, Chuanpeng ZHOU, Chuangwen XU, Zhong HUANG, Wei YU, Pengwei XUN, Jianbin HUANG, Xiaoyong MAI, Heizhao LIN
 doi: 10.12131/20210141
We evaluated the effects of dietary Clostridium butyricum supplementation on the growth performance and intestinal microbiota of juvenile Trachinotus ovatus, so as to provide a theoretical basis for the application of C. butyricum in T. ovatus aquaculture. In this study, five kinds of experimental feeds [0, 1% (1×107 CFU·g−1), 2% (2×107 CFU·g−1), 3% (3×107 CFU·g−1) and 4% (4×107 CFU·g−1) of C. butyricum] had been sprayed on the basic feed to feed T. ovatus for eight weeks. The results show that dietary supplementation of 2 % C. butyricum improved the feed utilization rate of juvenile T. ovatus significantly. The diversity of intestinal flora was significantly different from that in control group and 4% supplemental group (P<0.05). The principal co-ordinates analysis and principal component analysis show that the added amount of C. butyricum in the feed was the main factor for the change in the structure of the intestinal flora of juvenile T. ovatus. At phylum and genus level, C. butyricum supplemental group and control group show difference at different degrees. Dietary supplementation with C. butyricum improved the growth performance and intestinal health of juvenile T. ovatus.
Comparison of three methods of detecting aluminum content in jellyfish products
Wanqing SUN, Jianwei CEN, Shengjun CHEN, Jianchao DENG, Chuang PAN, Chunsheng LI, Kun ZHANG
 doi: 10.12131/20210112
In this paper, the content of aluminum in jellyfish (Rhopilema esculentum) was determined by inductively coupled plasma mass spectrometry (ICP-MS), spectrophotometry and EDTA titration. The differences of detection results, precision and accuracy were compared, and the advantages and disadvantages of three methods in industrial application were analyzed. The aluminum residue risk of ready-to-eat jellyfish in ten coastal cities of China was investigated by ICP-MS. The results show that there was no significant difference between ICP-MS and spectrophotometry. EDTA titration was different from the other two methods, but the difference was not significant. The relative standard deviation (RSD) of the three methods for salted jellyfish and ready-to-eat jellyfish ranged from 1.79% to 4.34%. The RSD of salted jellyfish and ready-to-eat jellyfish by ICP-MS were 92%−104% and 97%−100%, respectively. The RSD of spectrophotometry were 97%−102% and 98%−101%, respectively. The recovery of EDTA titration was 94%−99%, which were relatively low. The three methods all meet the testing requirements, and the appropriate testing method can be selected according to the actual needs. The results also indicate that the Al residue in ready-to-eat jellyfish in some areas is close to the national limit.
Cryopreservation of sperm of Acanthopagrus latus
Puyuan JIA, Huayang GUO, Kecheng ZHU, Baosuo LIU, Liang GUO, Nan ZHANG, Shigui JIANG, Dianchang ZHANG
 doi: 10.12131/20210083
Acanthopagrus latus, one of the important breeding species in China, whose sperm cryopreservation can provide technical supports for its breeding, prevent the decline of its germplasm resources and maintain its sustainable development of the breeding industry effectively. In this experiment, taking the spermatozoa of A. latus as experimental material, we screened the diluent, glucose concentration, antifreeze type and concentration as well as dilution ratio and cooling procedure. The results show that when the concentration of glucose was 10 g·L−1, 5% glycol was used as antifreeze, the dilution ratio was 1: 2, and the sperm was placed above the liquid nitrogen for fumigation at 4 ℃ for 30 m, then put into liquid nitrogen for storage for 2 h, the frozen sperm had the best motility after thawing in 37 ℃ water bath, the sperm motility, motility time and life span could reach (85.170±3.66)%, (9.16±70) s and (94.297±9.55) s, respectively.
Isolation, identification and biological characteristics of lactobacillus from grass carp
Nan WANG, Jiyuan YIN, Yingying WANG, Yingying LI, Siyu WU, Cunbin SHI, Jiahao LI, Jizhen CAO, Qing WANG
 doi: 10.12131/20210039
As the problem of aquaculture diseases is growing, the harm of using antibiotics and drugs is more and more serious and the research on ecological control technology is an important way to achieve healthy aquaculture. In this study, eight lactobacillus strains were isolated from the intestinal tract of the healthy grass carps (Ctenopharyngodon idella). The identification result indicates that all the eight strains were Lactobacillus plantarum. The results of biological characteristics evaluation show that L. plantarum strain Y190430 had a high growth rate, and it was sensitivity to common antibiotics. In addition, compared with the standard strain and commercial lactobacillus, L. plantarum Y190430 represented better tolerance to environmental stress such as acid, alkali, salt and temperature. Besides, it had a higher acid production rate and inhibitted the growth of pathogenic bacterias better. The results provide references for the research on ecological control of aquatic diseases.
Southwards cultivation and nutrition composition analysis of Marphysa maxidenticulata
Shuaipeng LI, Bin XU, Kun WANG, Minqiao HUANG, Dazuo YANG, Yibing ZHOU
 doi: 10.12131/20200222
In this paper, by using the "Northern worm and southern cultivation" method, we investigated the growth condition and nutritional composition of Marphysa maxidenticulata cultured in Beihai. The results show that the average body length of M. maxidenticulata grew up to (12.66±1.52) cm and the average body mass was (2.30±0.86) g within 240 d. The specific growth rate of M. maxidenticulata in mud sediments was significantly higher than that of the coarse sands at the early phase of culture, but the late phase of culture was just opposite. The results of nutrition composition analysis show that the nutritional composition contained 18 species amino acids in both cultured M. maxidenticulata in Beihai and wild M. maxidenticulata in Rushan, but their contents were significantly different (P<0.05). The contents of total amino acid, delicious amino acid, non-essential amino acid, semi-essential amino acid and essential amino-acid of cultured M. maxidenticulata in Beihai were higher than those of wild M. maxidenticulata in Rushan. In terms of fatty acid composition, 27 fatty acids had been determined in both cultured and wild M. maxidenticulata, and palmitic acid and oleic acid were the main fatty acids. There was no significant difference on the contents of saturated fatty acids and polyunsaturated fatty acids between cultured M. maxidenticulata in Beihai and wild M. maxidenticulata in Rushan. But the content of total monounsaturated fatty acids of cultured M. maxidenticulata in Beihai was significantly higher than that of wild M. maxidenticulata in Rushan (P<0.05).
Spatial analysis of fishing intensity for Illex argentinus based on fishing vessel tracks
Huimin SHI, Wei FAN, Han ZHANG, Shenglong YANG
 doi: 10.12131/20210010
In order to understand the spatial behavior of Illex argentinus fishing vessels, we had analyzed the Automatic Identification System (AIS) data from January to May, 2018. Based on data mining method, we identified the trajectories of squid fishing vessels, and drew the fishing intensity distribution map of squid fishing ground. Then we analyzed the spatial distribution characteristics of monthly fishing intensity of I. argentinus fishing ground. The results show that: 1) The velocity distribution of the squid jigging fishing vessels showed obviously bimodal distribution. 2) The period from January to April was the major squid jigging fishing season and the fishing effort was the highest. The fishing intensity of vessels from mainland China was high from February to April, and the vessels from other countries and regions mainly fished in April and May. 3) The monthly fishing effort was spatially autocorrelated and showed patterns of significant aggregation. 4) The analysis of cold and hot spots reveals that the fishing effort in the survey area showed an aggregated distribution in both high and low values, and the fishing hotspots were moving southward from January to May.
Biological characteristics of Epinephelus merra of coral reef waters in South China Sea
Yuanjie LI, Zuozhi CHEN, Jun ZHANG, Yan'e JANG, Yuyan GONG, Xiaofan HONG, Yutao YANG
 doi: 10.12131/20210105
Epinephelus merra is a representative species of coral reef fishes in the South China Sea. Based on the E. merra samples collected from the coral reef waters of Nansha and Zhongxisha Islands during 2018 and 2019, we investigated its biological characteristics such as age and growth, body length and weight, sex ratio and gonad maturity, feeding intensity and fatness, in order to gain an in-depth understanding of the growth pattern and population characteristics of the E. merra in the coral reef waters of the South China Sea. The results show that the dominant body length of E. merra in Nansha Islands was 80−160 mm; the allometric growth factor (b value) of the body length and body mass relationships was 2.783 5; the average of fatness was 2.24; the estimated parameters of the von Bertalanffy growth equation were L=183 mm, k=0.260 and t0= −1.268. The dominant body length of E. merra in Zhongxisha Islands was 110–160 mm; the b value of the body length and body mass relationships was 2.592 5; the average of fatness was 2.02; the estimated parameters of the von Bertalanffy growth equation were L=260 mm, k=0.128 and t0= −2.494. The age of 61 individuals in Nansha and Zhongxisha Islands ranged from 1 to 6 years old, and the dominant age group was 1–2 years old. The gonad maturities of the two sea areas were mainly at Stage II, while the feeding grade was mainly at Stage I. Compared with the Zhongxisha Islands, the E. merra stock in the Nansha Islands had smaller size and faster growth rate.
Preliminary study on species composition of spawn of Meiji Reef Lagoon in South China Sea based on DNA barcoding
Zhicheng LU, Min LI, Jun ZHANG, Shuai ZHANG, Hongting LI, Peiwen JIANG, Xiaolei CHEN, Yiting CAO, Zuozhi CHEN
 doi: 10.12131/20210091
Coral reefs, which have important ecological functions such as spawning and rearing, are the key habitats of marine fish. In this study, COI (Cytochrome c oxidase subunit I), part of mitochondrial DNA, was used as a marker to identify the fish eggs in Meiji Reef, and the species composition and the characteristic of seasonal variation were analyzed. The study indicates that there were 37 species of fish eggs in Meiji Reef, belonging to 3 orders, 23 families and 31 genera. Most species (33 species) were successfully identified to species level while 4 species were just identified to genera level. Fish eggs mainly belonged to Perciformes (91.89% of species, 97.31 % of total number). The main ecological type of fish eggs was reef-dwelling group (72.97%). The density of fish eggs was 0.95 ind.·m–3 in spring and 0.54 ind.·m–3 in autumn. The dominant egg species was defined as having a dominance degree greater than 0.001. The dominant roe species in spring were Pterocaesio tile, Pentapodus caninus, Upeneus tragula and Cephalopholis miniata. And the dominant roe species of autumn are Thunnus albacares and Scolopsis taenioptera. The species replacement rate of fish roe in Meiji Reef between spring and autumn was as high as 94.59%. The indices of average taxonomic distinctness of spring and autumn were 53.63 and 50.77, respectively, and the indices of variation in taxonomic distinctness were 111.45 and 31.03, respectively. The results show that Meiji Reef is the spawning ground for a variety of commercial fishes and deep-sea fish and oceanic migratory fish (like T. albacares). The community structure of fish eggs in Meiji reef has obvious seasonal variation, showing that coral reef fish has high utilization of specific habitats.
Decadal change in biological traits of Collichthys lucidus in Pearl River Estuary
Pengli XIONG, Zuozhi CHEN, Gang HOU, Shuai ZHANG, Yongsong QIU, Jiangtao FAN, Shannan XU
 doi: 10.12131/20210072
Based on Collichthy lucidus samples collected by setnet and gillnet in the Pearl River Estuary during January to April of 1986−1987, January to February of 2018 and March to April of 2019, we analyzed the decadal change in biological traits of C. lucidus including population structure, growth, feeding grade and so on. The results show the dominant body length group was 90−110 mm, and the average body length was (95±13) mm and (93±18) mm. There was no significant difference in the average body length between the two decades (P>0.05), but the proportion of individuals in the dominant body length group decreased (P<0.05). The body length of 50% sexual maturity was significantly shortened. From 1986 to 1987, the length of the first sexual maturity of the female population was 112 mm, but from 2018 to 2019, it was shortened to 88 mm. The fatness, feeding grade and the proportion of males in the spawning population showed an upward trend. During 2018−2019, the average fatness and average feeding grade of the population, female and male were higher than those in 1986−1987 (P<0.05). From 1986 to 1987, there was a significant difference in the average feeding grade between male and female individuals (P<0.05), but there was no significant difference in the average feeding grade between spring and winter (P>0.05) and in the average fatness (P>0.05). From 2018 to 2019, there were significant differences in average fatness and average feeding grade between male and female individuals (P<0.05). There were significant differences in average feeding grade between spring and winter, and the average feeding grade in winter was higher than that in spring (P<0.05).
Genetic diversity of silver carp (Hypophthalmichthys molitrix) in lower reaches of Yangtze River based on microsatellite markers
Yuting LUO, Di'an FANG, Yanfeng ZHOU, Dongpo XU, Yunxing PENG, Fei PENG, Guining ZHANG, Kai LIU, Yang YOU
 doi: 10.12131/20210067
In order to understand the genetic diversity and distribution of silver carp (Hypophthalmichthys molitrix) in the lower reaches of the Yangtze River, we used microsatellite markers combining with capillary electrophoresis to analyze 327 DNA samples of silver carp from eight wild populations in Yangtze River sections (Hukou, Anqing, Wuhu, Dangtu, Zhenjiang, Jingjiang, Zhangjiagang and Changshu sections) from 2017 to 2019, so as to investigate their genetic diversity, genetic differentiation and genetic structure. The results show that the genetic diversity of the eight populations was high. However, heterozygotes were not enough in the populations. The number of alleles ranged from 6.00 to 12.3, while the number of effective alleles ranged from 3.94 to 6.10. The observed heterozygosity and expected heterozygosity ranged from 0.617 to 0.719 and from 0.658 to 0.774, respectively. The unbiased expected heterozygosity ranged from 0.671 to 0.782. The Shannon's information index ranged from 1.38 to 1.86, and the inbreeding coefficient ranged from 0.001 to 0.174. Genetic differentiation analysis shows that the Fst value ranged from 0.006 to 0.068, while gene flow ranged from 3.41 to 41.9. Genetic distance ranged from 0.001 00 to 0.106. Hukou population showed a moderate degree of genetic difference with other populations, while the genetic differences among other populations were small. Analysis of molecular variance shows that the variation mainly came from within the population (97.6%). Genetic structure analysis shows that Hukou population had different gene pool from other populations. The river-lake connectivity may be of positive significance for silver carp to show unique genetic differentiation characteristics in Hukou section of the Yangtze River. Therefore, whether the formation of this population differentiation is caused by the spatial isolation of geographical distance or the physiological barrier of habitat difference needs to be further studied.
Effects of Jet Water Mixer on physicochemical parameters and bacterial abundance in Apostichopus japonicus pond
Dongsheng ZHANG, Zufeng WANG, Wei ZHOU
 doi: 10.12131/20210065
Jet Water Mixer (JWM) is a set of new water quality improvement equipment. To evaluate the effect of JWM on the pond water quality improvement, we monitored seven physicochemical parameters, including temperature, salinity, pH, dissolved oxygen (DO), total ammonia nitrogen (TAN), nitrous nitrogen (NO2 -N), phosphate (PO4 3+-P), contents of sediment organic matter (TOM), abundance of living heterotrophic bacteria and culturable vibrio in the ponds of Dalian Zhuanghe Sea Cucumber Farm. The results show that compared with the control group, the contents of TAN and NO2 -N were the lowest from March to November except for June; the PO4 3−-P content was the highest from March to August in JWM pond; the TOM content was the lowest in each month (P<0.05). At thermocline and halocline stage, JWM increased the DO content significantly. JWM promoted the growth of living heterotrophic bacteria and inhibitted the growth of Vibrio as long as 8−9 months. It is concluded that JWM can improve water quality and reduce abundance of Vibrio in the water in spring, summer and autumn significantly, and reduce TOM content throughout the year, so it has a good application prospect in the cultivation sea cucumbers.
Effect of enzymatic hydrolysate products of oyster on lactation in overloaded lactation rats
Suhua CHEN, Xiaoming QIN, Chaohua ZHANG, Wenhong CAO, Huina ZHENG, Haisheng LIN
 doi: 10.12131/20210139
Taking the enzymatic hydrolysate of Crassostrea hongkongensis as subjects, we used overloaded lactation model to investigate the effects of oyster enzymatic hydrolysate products (OEHP) on lactation of postpartum overloaded lactating rats by measuring the lactation volume of female rats, total average body mass increment of offspring, organ index of female rats, mammary gland organ index of female rats and serum prolactin (PRL). The mammary gland structure was observed by HE staining method. The results show that within 21 d of gavage, compared with control group, the increase of hourly lactation was significant in high dose group, but not significant in low dose group, positively correlated with the dose. The total average lactation of high dose group increased by 57.85% (P<0.01); for low and medium dose groups, the lactation growth was 38.02% (P<0.05) and 17.69%, respectively. The body weight gain of young mice in high, medium and low dose groups increased by 13.62%, 12.28% and 11.99%, respectively (P<0.01). There was significant difference in the body weight gain between high dose group and medium, low dose groups (P<0.05). The mammary gland index had significant difference. The organ index increased to varying degrees. The concentration of prolactin PRL in high-dose group increased by 41.67% (P<0.01). The prolactin concentration in medium-dose group increased by 26.39% (P<0.05), and that in low-dose group increased by 11.11%. Compared with low dose group, the concentration of prolactin in high dose group increased by 27.50% (P<0.05). In addition, the mammary gland structure of female rats in each group had obviously enlarged and filled, which indicates that OEHP can improve the regulation of lactation within overloaded lactation rats effectively and promote lactation.
Analysis of muscle components of striped jack (Pseudocaranx dentex)
Yan JIANG, Xuezhou LIU, Aijun CUI, Kaijie WANG, Bin WANG, Yongjiang XU
 doi: 10.12131/20210095
Striped jack (Pseudocaranx dentex) is the source of superior ingredients such as sashimi and sushi because of its fresh and delicious taste. To evaluate its muscle nutrition value, we analyzed its nutritional components by biochemical technology. The results show that the muscle had higher crude protein content. At amino acid level, the essential amino acids accounted for 40.67% of the total amino acids, and the delicious amino acids accounted for 35.37% of the total amino acids, which meets the ideal protein standard recommended by Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO). According to the amino acid score (AAS) and chemical score (CS) values of essential amino acids, methionine was the first limiting amino acid for striped jack, followed by valine. Moreover, the content of unsaturated fatty acids in the muscle of striped jack was as high as 73.73%, the content of EPA+DHA was 21.20%, and the content of n-3 PUFA was 1.95 times that of n-6 PUFA, implying that striped jack can supply excellent unsaturated fatty acids for people. Furthermore, the muscle of striped jack contained a variety of mineral elements which are necessary for human body tissues and normal physiological activities. Therefore, the striped jack is an economic fish with great development potential for its higher protein content and excellent taste.
Differential analysis of microRNAs in zebrafish gills under hypoxic stress
Feng LIN, Ruonan JIA, Faxiang WANG, Qianghua XU
 doi: 10.12131/20210124
In order to study the biological function of microRNAs (miRNAs) in response to hypoxic stress, we perfomed high-throughput miRNAs sequencing in the gill tissues of zebrafish (Danio rerio) under hypoxic stress and normoxic condition, and analyzed the differences in miRNAs expression in the gill tissues of zebrafish. The results show that a total of 15 miRNAs are significantly differentially expressed in the gills of zebrafish under hypoxic stress and normoxic condition, among which 13 miRNAs were up-regulated significantly and 2 miRNAs were down-regulated significantly. Moreover, we performed a correlation analysis on miRNAs sequencing and zebrafish gill transcriptome, and predicted the target genes for 28 heat shock protein genes that were significantly differentially expressed under hypoxic stress and normoxic condition screened in the previous stage. The result shows that miR-455-3p, which was expressed significantly low under hypoxic stress, targeted to increase the expression of hspa14 and dnajb6b at the same time to enhance the adaptability to hypoxic stress. In addition, miR-194a and miR-155, which were highly expressed under hypoxic stress, targeted five heat shock protein genes (hspa12a, dnajc5aa, hspb7, hsp70.3, dnajb2) and four heat shock protein genes (hspa12a, hspg2, hspa13, dnajb2) to regulate zebrafish's adaptation to hypoxic condition.
Study on main catch composition and fishing ground change of light purse seine in Northwest Pacific
Guoqing ZHAO, Yongchuang SHI, Wei FAN, Xuesen CUI, Fenghua Tang
 doi: 10.12131/20210086
The light purse seine fishery in the high seas of the Northwest Pacific has been a new kind of pelagic fishery developed in China in recent years, with a certain development potential. Understanding the catch composition and fishery change of light purse seine is important for the fishery management and development in the Northwest Pacific Ocean. Based on the statistical data from 2014 to 2019, the paper makes a statistical analysis on the catch, the catch per unit effort (CPUE) and the main catch composition. Besides, the seasonal variation of the distribution of the fishing ground gravity center is discussed through the method of gravity center of catch and cluster analysis. The results show that: 1) There was a big difference in the annual catch yield and CPUE. Generally, the yield increased first and then decreased, and CPUE decreased year after year. 2) A total of eight species were found, among which Scomber japonicus was the main catch species with a frequency of 100%, followed by Sardinops sagax with a frequency of 87.5%, and the catch of other species was relatively small. 3) The center of gravity of the fishing ground gradually moved to the northeast from April, and turned back to the Southwest after reaching the northeast from August to October, showing a certain anticlockwise variation. The center of gravity of the fishing ground gradually moved to the northeast, and the center of gravity moved 0.92° east in longitude and 1.57° north in latitude from 2014 to 2019. 4) The clustering results show that the monthly yield barycenters could be divided into four categories (July, August, September and October, May and November, April, June). The annual yield barycenters could also be divided into four categories (2016, 2017 and 2018, 2019, 2014, 2015), indicating that there were certain inter-annual and seasonal changes in the light purse seine fishing grounds in the Northwest Pacific.
Study on attraction effect of artificial reefs vertical plate with different square apertures on Sparus macrocephalus
ZHANG Haoming, XIE Xiaoyan, CHEN Pimao, YUAN Huarong, FENG Xue, TONG Fei, LIU Yan, CHEN Zhijian, ZOU Jianhao, CHEN Zicong
 doi: 10.12131/20210103
Construction of artificial reefs is an important measure to restore marine habitats and conserve fishery resources. Reinforced concrete reefs are commonly used types of artificial reefs. The square apertures of the reef vertical plates (Side plates and spacer plate) are made of reinforced concrete reefs. The main structure, the square aperture of the vertical plate is an important factor that affects the fish trapping. In order to observe the attractive effects of different square apertures of reef vertical plates for juvenile black sea bream (Sparus macrocephalus), we used different square pore-size to study the attractive effect on the juveniles. The results show that the average occurrence rate of the juveniles was 2.56% in A1 area of blank reef area in the control group, and that of group B1 (aperture 8 cm) was 9.89%, followed by 9.01% in B3 (aperture 24 m), 7.65% in B2 (aperture 16 cm), 6.80% in B5 (aperture 40 cm) and 5.25% in B4 (aperture 32 cm) after the reef vertical plate was placed. The fish fins were about 2, 6, 4, 10 and 8 times, respectively. Statistical analysis shows that five groups of square aperture vertical plates have certain trapping effect, among which group B1 with 8 cm hole diameter of reef vertical plate has the best effect, but there is no obvious difference between the square hole diameters of reef vertical plate.
Effect of different drying methods on volatile components of tilapia fillets analyzed by electronic nose combined with GC-MS
LUO Jing, LI Min, ZHANG Ying, LIU Yan, GUAN Zhiqiang
 doi: 10.12131/20210098
To investigate the effect of drying method on the volatile flavor components of tilapia fillets, and to provide references for the processing of tilapia fillets, four dried tilapia fillets were obtained by ultrasound-assisted polydextrose osmotic heat pump drying (UAPOHPD), heat pump drying (HPD), ultrasound-assisted polydextrose osmotic vacuum freezing-heat pump combined drying (UAPOVFHPCD), vacuum freeze drying (VFD), respectively, and their volatile components were analyzed by electronic nose combined with HS-SPME-GC-MS. The volatile flavor components of tilapia fillets were analyzed by principal component analysis (PCA), and the key flavor components of different dried products were determined by the relative odor activity value. The results show that the electronic nose could better distinguish different dried tilapia products. The fresh tilapia fillets, UAPOHPD products, HPD products, UAPOVFHPCD products and VFD products had three, five, five, four and five key flavor components, respectively. The comprehensive score of HPD products was the highest, followed by UAPOHPD products, VFD products and UAPOVHFPCD products.
Antimicrobial spectrum, resistance gene detection and ERIC-PCR genotyping of Vibrio scophthalmi
SHEN Fei, ZHAI Yufei, WANG Hao, LÜ Liqun
 doi: 10.12131/20210138
From June to October of 2020, we had isolated 394 strains from diseased turbot (Scophthalmus maximus) in Liaoning Province, and identified them based on the 16S rRNA sequence. Then we randomly selected 18 Vibrio scophthalmi strains, which were further typed by enterobacterial repetitive intergenic consensus PCR (ERIC-PCR), to analyze the susceptibility to 8 antibiotics and the presence of drug-resistance genes. The results show that most of the isolates were Vibrio with 232 strains (58.88%), among which 117 strains (29.70%) were V. scophthalmi. The 18 strains identified by rpoD sequence alignment were not resistant to neomycin sulfate, flumequine and doxycycline hydrochloride, and resistant to other five antibiotics with different ratios. The multiple drug resistance rate was 66.7%. Five drug resistance genes in the 18 strains of V. scophthalmi were detected with amide alcohol resistance genes floR of 61.11% and cmlA of 66.67%, sulfonamide resistance gene sul2 of 55.56%, quinolone resistance genes qnrA of 50% and qnrS of 5.56%. No aminoglycosides and tetracycline resistant genes were detected. The coincidence rate of amide alcohol resistance genes and drug resistance phenotype was 88.89%, indicating a certain correlation between them. Sulfonamide resistance genes had a coincidence rate of 50% with the resistance phenotype, and quinolones resistance genes had the lowest coincidence rate of 33.33%. Finally, the 18 strains were clustered into four types using ERIC-PCR fingerprinting. Type Ⅰ (44.44%) and type Ⅲ (44.44%) were the main clusters. We observed apparent absence of correlation between ERIC-PCR fingerprinting and the resistance phenotype or resistance genes. Thus, it is conluded that doxycycline hydrochloride can be the first choice for the control of V. scophthalmi in Liaoning aquaculture farms.
Growth characteristics and production performance analysis of new scallop strain "Zihaimo" F4
ZHANG Yuan, LIU Zhigang, WANG Chunde, YAO Gaoyou, ZHANG Kexin, ZHAN Jianqiang, CHEN Linguang, LU Wengang, ZHONG Maocheng, LIUFU Shaomei
 doi: 10.12131/20210156
To assess the effects of the production performance of the scallop new strain "Zihaimo" and provide references for the breeding effect of the new strain, we conducted a research in the same sea area with the same management mode and breeding cycle. By comparing seven traits of scallop farming population including shell length (SL), shell height (SH), shell width (SB), body weight (BW), adductor muscle weight (AW) and shell weight (SW) and survival rate of the new strain "Zihaimo" F4 with the Argopecten irradians concentricus, we analyzed their growth characteristics and production performance. The results indicate that the accumulated survival rate of "Zihaimo" F4 was 51.32% when it was cultured from October 13th to April 28th of the next year, and the shell length was from 1–1.5 mm to 50–60 mm, which was significantly greater than 29.18% of A. i concentricus (P<0.01). However, the SL, SH, SB and SW of the two cultivation groups in the same period had extremely significant differences (P<0.01). It is suggested that the growth rate of the new strain "Zihaimo" F4 was higher than that of A. i concentricus. Compared with A. i concentricus, after 6.5 months of cultivation, the SL, SH, SB, BW and AW of the new strain "Zihaimo" F4 increased by 19.50%, 19.84%, 16.23%, 56.30% and 20.20%, respectively.
Transcriptome analysis of Plectropomus leopardus liver under different flow velocity
GAO Jin, WANG Yongbo, LIU Jinye, GUO Yilan, FU Shuyuan
 doi: 10.12131/20210125
Water flow velocity is one of important eco-environment factors which effects on fish growth. In order to explore the function and expression of related genes under different flow velocity of Plectropomus leopardus, the transcriptome analysis of liver tissue of P. leopardus under different flow velocity was conducted by RNA-seq technology. In this study, we selected the fish fry of P. leopardus with identical size from the same breeding batch and cultured for 150 d with water flow velocity of 0.1 m·s−1 (Low flow velocity, LFV) and 0.4 m·s−1 (High flow velocity, HFV). Then, we conducted a transcriptome analysis on the liver so as to investigate the difference of gene expression patterns with different flow velocities. We had obtained a total of 1 977 differentially expressed genes (DEGs) by transcriptome analysis (999 up-regulated and 978 down-regulated for LFV-HFV, respectively). The GO functional annotation reveals that 1124 DEGs were annotated in Gene Ontology Consortium and assigned to 56 functional terms. KEGG pathway analysis shows that 573 DEGs belonged to 154 pathways, and PPAR signaling pathway was most significantly enriched. Histological observation of livers of tested fish indicates that the difference of fat contents between LFV and HFV group was significant, and the fat content was obviously higher in LFV than in HFV (P<0.05). According to the transcriptome analysis, we excavated many DEGs under different flow velocity, which provided technical support for further research on the molecular regulation mechanism of adaptability to change in flow velocity of P. leopardus.
Feeding biology of yellowfin tuna (Thunnus albacares) in tropical central and western Pacific Ocean
SHI Xiaofei, WANG Xiao, WANG Yixi, SHI Jiangao, ZHANG Jian
 doi: 10.12131/20210140
The yellowfin tuna (Thunnus albacares) had been collected in the tropical central and western Pacific Ocean (163°14'E−173°35'E, 2°03'S−11°17'S) from May 2018 to February 2019 by pelagic longline fishing trageting tunas. In total, 919 individuals were collected and the size frequency and sex ratio were analyzed. The feeding biology of 551 individulas was studied. The effects of fork length, fishing water depth and lunar phase on feeding biology were analyzed by analysis of variance (ANOVA) and generalized linear mixed model (GLMM). The results show that: 1) the fork length range was 87−163 cm, and the sex ratio (female to male) was 1: 1.32. 2) The hollow stomach rate accounted for 33.76%. For tunas with non-empty stomach, the frequency of presense of sardines, squid and miscellaneous fish in stomach contents were 52.60%, 35.34% and 33.70%, respectively. 3) The ANOVA results show that the differences in Shannon-weiner diversity index (H') and Pielou evenness index (J') among different fork length groups and lunar phases were significant, while the differences among water aqueous layer and months were insignificant. 4) The feeding intensity was mainly at 0−2 level, and the empty stomach rate increased as the fork length increased. The proportion of high feeding intensity (level 2−4) increased gradually as water depth increased. 5) The result of GLMM model fit shows that biological factors (fork length and gender), spatial and temporal factors (the cosine of lunar phase and water depth) had significant effects on the feeding intensity of yellowfin tuna.
Preliminary study on distribution characteristics and positioning of microsatellites in whole genome of Pelteobagrus vachelli
PENG Ye, LI Jie, WANG Tao, ZHANG Kai, NING Xianhui, JI Jie, YIN Shaowu
 doi: 10.12131/20210168
In this study, MISA (MIcroSAtellite identification tool) was used to screen and analyze the distribution characteristics of microsatellites in the whole genome of Pelteobagrus vachelli, aiming to provide a basis for the selection of functional microsatellite markers. The genes containing microsatellites in the exon regions were subjected to GO annotation and KEGG enrichment. In the whole genome of P. vachelli (Approximately 663.53 Mb), 417 724 perfect microsatellites were identified, accounting for 1.48% of the total length. The relative abundance of microsatellites in P. vachelli was 630 pcs·Mb−1. Among the six repeat types, dinucleotides were the most frequent, accounting for 43.36% of the total microsatellites, followed by mononucleotides (39.02%), tetranucleotides (9.05%), trinucleotides (7.34%), pentanucleotides (1.12%) and hexanucleotides (0.12%). By investigating the locations of microsatellites in the genome, we found that 10 924 microsatellites which belonged to 5 788 genes were located in the exons. The GO annotation shows that the genes annotated as biological process were with the highest amount, mainly associated with binding activity and cellular macromolecular metabolism. KEGG enrichment analysis shows that these genes were enriched in 273 pathways, among which, flavonoids and flavonol biosynthesis (P=0) were the most significantly enriched pathways. Integrated analysis indicates that the microsatellites located in the exons of genes in P. vachelli were closely related to the biological metabolism processes.
Analysis of ontogenetic phenotype changes of Enoploteuthis chunii beak
BU Xinyu, LIU Bilin, OU Liguo, LI Jianhua, FANG Zhou, LIU Yan
 doi: 10.12131/20210135
Cephalopod beak is an important hard tissue that records lots of growth information. In the Northwest Pacific Ocean, Enoploteuthis chunii is the prey of many marine mammals and fishes. Understanding phenotype changes in the growth of beak not only helps us to know E. chunii ontogenetic trophic ecology variation, but also helps us to investigate its ecological role in the system. In this study, the ontogenetic changes in beak phenotype were investigated by analyzing the variation of beak length and pigmentation of 91 squids, which were collected in the Northwest Pacific Ocean in March and September in 2019. AIC analysis shows that beak length and pigmentation of the squids had positive relationship with increasing mantle length. The beak length saltated in 31 mm and 41 mm. The upper crest length (UCL), lateral wall length (ULWL) and lower lateral wall length (LLWL) had high linear regression slope, which indicates that they grew faster than other beak parts. The proportion of pigmentation in the upper hood length (UHL), lower hood length (LHL) and LLWL saltated in 31 mm, but the proportion of pigmentation in ULWL saltated in 41 mm. ANOVA analysis showed significantly phenotypic changes of E. chunii beak (P<0.05). The study of ontogenetic phenotype changes such as size and pigmentation will provide references for study on ontogenetic feeding shift.
Growth, maturity and mortality of Johnius distinctus and J. belangerii in offshore waters of southern Zhejiang Province
PEI Rude, MA Qiuyun, TIAN Siquan, ZHANG Yunfei, FAN Qingsong
 doi: 10.12131/20210058
Karut croaker (Johnius distinctus) and Belanger's croaker (J. belangerii) are common small economic fishes and important prey species in ecosystem of the East China Sea. Research of their biological characteristics are essential to understand the ecosystem and to improve the scientific management of these important fisheries in the East China Sea. Based on the seasonal surveys of fishery resources in the offshore waters of southern Zhejiang Province, we applied linear mixed effects model (LMEF) to study the growth characteristics and heterogeneity of the two species. The limiting body length (L), growth rate (k) and theoretical growth starting age (t0) were estimated by ELEFAN method. The natural death coefficient (M), total death coefficient (Z), development rate (E), and the 50% sexual mature body length of the two species were estimated. The LMEM results show that seasons have the most significant effect on their growth. For J. distinctus, L=216.83 mm, k=0.84, t0=−0.1; for J. belangerii, L=207.38 mm, k=0.63, t0=−0.25. For J. distinctus, Z=3.80, M=1.53, E=0.60; for J. belangerii, Z=1.88, M=1.24, E=0.34. The length of 50% maturities were 133.1 mm and 128.9 mm for J. distinctus and J. belangerii, respectively.
Description of Euthynnus affinis vertebrae and appendages
ZHOU Shengjie, YANG Rui, YU Gang, MA Zhenhua
 doi: 10.12131/20200175
In order to reveal the bone morphology of Euthynnus affinis, we studied its X-ray photography. The fish consisted of 20 trunk vertebrae and 18 tail vertebrae. The 4th–30th vertebrae connected with 27 spinal spines. The 16th–28th vertebrae extended downward and connected to each other to form a special bone structure. The upper and lower sides of the 35th–37th vertebrae extended obliquely to the rear to form three supraccaudal bones and three lower tail bones. The back half of the 38th vertebra evolved into a whole tailbone. The shoulder girdle was located at the 5th–6th vertebrae. The girdle bone was located below the 6th spine. The 1st dorsal fin was located above the 6th–16th vertebrae. The 2nd dorsal fin was located above the 21st–24th vertebrae. The anal fin was located below the 23rd–26th vertebrae. There were 7–8 small fins behind the dorsal fin, and the branch fin bone extended between the two spinal spines. There were 6–7 small fins behind the anal fin, and the fin bones extended between the two spines.The research results show that the X-ray method can observe the bones of E. affinis clearly, but the head bones are not clear because of more overlapping; the X-ray method can achieve harmless fish bone research; in order to adapt to high-speed swimming in the sea, E. affinis has a unique bone structure. The study of bones of E. affinis enriches the research of tuna in the South China Sea, providing references for its classification and evolution, as well as providing ideas for the harmless study of rare fish.
Effects of aquaculture water color on survival, growth and body color of Cherax quadricarinatus juveniles
LIAO Xiurui, YANG Jinling, WEI Miao, LI Jiaoni, PAN Zhi, SHI Yaohua, VASQUEZ Herbert Ely, LIU Chunsheng, GU Zhifeng, ZHENG Xing
 doi: 10.12131/20210128
In this study, artificial pigments were added to regulate the color of aquaculture water (yellow, blue, green). Transparent aerated running water was used as the experimental control group to explore the effects of aquaculture water color on the survival, growth and body color of juvenile Cherax quadricarinatus. The results show that the survival rates of the control group, yellow and blue experimental groups were all about 50%, while that of the green experimental group was lower (33.33%, P<0.05). The weight gain rate, specific growth rate, body length and body width of the green experimental group were the highest, which were significantly higher than those of the control group (P<0.05). There was no significant difference between the yellow and blue experimental groups and the control group (P>0.05). The body color of juveniles in the blue experimental group was blue (∆E=21.35), yellow (∆E=18.23) and green (∆E=17.35). There were significant differences in the body color between different parts of the juveniles, and the lightness value of dorsal carapace (L*) was significantly lower than that of the large claw and tail; the redness value (a*) of dorsal carapace was higher than that of large claw and tail; the yellowness value of tail (b*) was higher than that of large claw and dorsal carapace. Blue water can improve the b* value of dorsal carapace significantly.
Fish size spectrum characteristics in offshore waters of southern Zhejiang Province
YANG Ke'er, ZHOU Xijie, QIN Song, MA Jin, ZHAO Jing
 doi: 10.12131/20210090
In order to improve the understanding of the spatial and temporal characteristics, seasonal variation and influencing factors of size structure of offshore fish communities in southern Zhejiang, we studied the characteristics of fish particle size spectrum and its spatiotemporal variation by means of particle size spectrum and multi-dimensional scale sorting based on the seasonal fishery survey data in 2019. The results show that the shape of annual Sheldon fish size spectrum was generally unimodal, and the size class ranged from −2 to 11, with the highest biomass occurring in the size classes of 6~7, mainly small fishes. The Sheldon fish size spectrum was basically unimodal in four seasons, and there were seasonal differences in the peak and maximum biomass corresponding to the size range and species composition. The fitted curves for the normalized fish size spectrum were all dome-shaped, and the curvature ranged from −0.18 to −0.09, with the maximum in winter (−0.09) and the minimum in spring (−0.18), indicating that fish biomass was the most vulnerable to external disturbance in spring but relatively stable in winter. The results of multidimensional scaling demonstrate that the fish community in this study can be classified into four subgroups in winter and spring, and three subgroups in summer and autumn. The analysis of size spectra by subgroups shows that the nearshore fish community is much affected by external disturbances than the far-shore fish community. In general, the fish community off southern Zhejiang Province is in a disturbed state, which may be related to environmental factors, seasonal migratory and sedentary fishes, as well as the closed fishing periods and fishing activities.
Genetic diversity analysis in six different geographical populations of Lateolabrax maculatus by microsatellite markers
HUANG Hao, FAN Sigang, WANG Pengfei, CHEN Jia, ZHAO Chao, YAN Lulu, QIU Lihua, PAN Ying
 doi: 10.12131/20210126
In order to analyze the genetic structure of Lateolabrax maculatus, we selected 11 polymorphic microsatellite loci from L. maculatus genome sequence to investigate the geneticstructure of six wild populations of L. maculatus. All of wild L. maculatus were fished from the coast of Tianjin, Qingdao, Changdao, Shanghai, Xiamen and Beihai, China, respectively. A total of 57 alleles were detected from 11 polymorphic microsatellite loci and 7 microsatellite loci were highly polymorphic loci. Among the six populations, the number of alleles (Na) was 3.909 3–4.636 4 and the effective number of alleles (Ne) was 2.293 4–2.773 5. The observed heterozygosity (Ho) was 0.391 3–0.456 8 and the expected heterozygosity (He) was 0.505 1–0.566 2. The polymorphism information content (PIC) was 0.388 8–0.518 9. The populations of L. maculatus from Qingdao, Shanghai and Beihai were highly polymorphism, and the other populations were moderate polymorphism. The Shanghai population was highest polymorphism among all the populations. Changdao and Xiamen populations were low polymorphism. The genetic differentiation index (FST) was 0.022 6–0.055 2. The genetic differentiation among the six population was low and the highest genetic differentiation was detected between Tianjin population and Beihai population. The gene flow (Nm) was 4.276 6–11.220 8, and the most frequent gene exchange was found among these populations. The analysis of molecular variance (AMOVA) shows that the variation among populations accounted for 91% and the variation within populations accounted for 9%. The cluster analysis based on individual classification shows that the individuals of six populations were divided into two genotype groups and no independent genotype group was detected. The UPMGA cluster tree based on genetic distance shows that six populations were divided into two branchs. The study provides references for the genetic breeding of L. maculatus.
Spatial and temporal variability of habitat distribution of Sthenoteuthis oualaniensis in South China Sea and its interannual variation
FAN Jiangtao, YU Wei, MA Shengwei, CHEN Zuozhi
 doi: 10.12131/20210115
We developed an integrated habitat suitability index (HSI) model to examine the spatio-temporal distribution of potential habitat of Sthenoteuthis oualaniensis in the South China Sea in spring and clarify the law of the spatio-temporal distribution of habitat of the fish, based on the fishery data of S. oualaniensis and three critical environmental factors including sea surface temperature (SST), Chlorophyll-a (Chl-a) and sea surface height (SSH). Results show that the SST and SSH on the fishing ground of S. oualaniensis were lower in the northern waters but higher in the southern waters. The Chl-a concentration was higher in the coastal waters but lower in the pelagic waters. The suitable habitats of S. oualaniensis in spring mainly distributed in the regions between 110°E and 119°E, and its spatial location was consistent of the overlapping areas among the suitable environmental ranges of the above-mentioned three factors. Besides, the HSI anomaly from 2014 to 2017 gradually decreased and showed interannual variability in space. Annually suitable range of each environmental factor exhibited decreasing trend, and the unfavorable range of each environmental factor showed an increasing trend, leading to the contracted suitable habitats and enlarged unfavorable habitats for S. oualaniensis. The longitudinal and latitudinal distribution of suitable habitats of S. oualaniensis also showed significant interannual variability from year to year. The results indicate that the habitats of S. oualaniensis are closely associated with the environmental factors on their fishing ground; the variability of spatial and temporal of potential habitat hotspots can be explained by the spatio-temporal distribution of environmental conditions.
Comparative study on feeding frequency of hybrid F2 of Acanthopagrus schlegelii ♀ × Pagrus major♂ and A. schlegelii
QIU Yuyan, ZHANG Zhiyong, CHEN Shuyin, NI Kewen, JIA Chaofeng, MENG Qian, ZHU Fei, ZHANG Zhiwei, TANG Xiaojian
 doi: 10.12131/20210081
In order to study and compare the differences of growth performance, physiological and biochemical indexes between the hybrid porgy (HF2) of Acanthopagrus schlegelii♀ (black porgy) ×Pagrus major♂ (red porgy) and A. schlegelii with different feeding frequencies, we selected the HF2 and A. schlegelii juveniles as the research objects, and set four feeding frequency groups: once·d −1, twice·d−1, 3 times·d−1 and 4 times·d−1 (marked as 1 T, 2 T, 3 T and 4 T), and carried out a 40-day breeding experiment. The results show that when the feeding frequency increased from 1 T to 2 T, the weight gain rate (WGR), specific growth rate (SGR) and survival rate (SR) of the HF2 and A. schlegelii increased significantly (P<0.05), while the activities of pepsin, lipase and α-amylase decreased significantly (P<0.05). There was no significant difference in the WGR, SGR, SR and digestive enzyme activities among the HF2 and A. schlegelii groups (P>0.05). When the feeding frequency was more than 2 T, there was no significant difference in the WGR, SGR, SR and digestive enzyme activity between among experimental groups (P>0.05). There was no significant difference in the antioxidant enzyme activity between 3 T and 2 T groups (P>0.05), but significantly higher than that in 4 T group (P>0.05). In addition, under the same feeding frequency, the WGR, SGR, pepsin and lipase (LPS) of the HF2 in 2 T group were significantly higher than those of A. schlegelii, the catalase (CAT) and total superoxide dismutase (T-SOD) of the HF2 in 4 T group were significantly higher than those of A. schlegelii (P<0.05). Therefore, the optimum feeding frequency of the HF2 and A. schlegelii juveniles is 2 T, and the growth performance of the HF2 was obviously better than that in A. schlegelii among all the experimental groups.
Population genetic structures of Dosidicus gigas in Southeast Pacific Ocean based on mitochondrial NADH dehydrogenase subunit 2 gene
XU Hao, LIANG Xuhong, WANG Congcong, LI Gang
 doi: 10.12131/20210119
To understand the genetic differentiation and structure among the large, medium and small phenotypic groups of Dosidicus gigas in the Southeast Pacific, a total of 90 samples of matured D. gigas from different phenotypic groups were studied for population genetics using the mitochondrial NADH dehydrogenase subunit 2 (ND2) gene. The average haplotype diversities (Hd) and nucleotide diversities (Pi) of the three groups of D. gigas were 0. 818 and 0.002 40, respectively, showing a high haplotype diversity index and a low nucleotide diversity index. The genetic variation observed within populations reached 100.45%. The value of genetic differentiation index Fst was less than 0.05 (P>0.05), and the gene flow (Nm) was far more than 1, indicating no significant genetic divergence among the three phenotypes of D. gigas. The neutrality test was highly significantly negative (Fs=−8.617 73, P<0.01) and the nucleotide mismatch distribution curves all showed significant single peaks, suggesting that D. gigas in the Southeast Pacific might have historically experienced rapid population expansion events. In conclusion, there may be extensive genetic exchange between different phenotypic groups of D. gigas in Southeast Pacific Ocean due to their reproductive behavior and that they should belong to the same stock, which should be be fully considered in fisheries management.