2010  Vol. 6  No. 1

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Research Paper
Abstract:

In this paper, a concrete-made artificial reef model with the shape of hexahedral cone was put into the experimental tank to observe the attraction effects of the artificial reef model on Plectorhynchus cinctu under three illumination conditions of natural illumination, 55 W and 26 W. The results showed that without the artificial reef model in the trough, the fish tended to stay in the areas on the left of the trough. The average occurring rate of the fish in these areas under the 3 different kinds of illumination were 61.60% (natural illumination), 81.61% (55 W) and 82.07% (26 W), but it was less than 5% inside the blank reef areas.After the artificial model was put into the troughs, the average occurring rate of the fish inside the reef areas increased to 37.60% (natural illumination), 23.56% (55 W) and 15.75% (26 W), while that in the left areas of the trough reduced to 23.47% (natural illumination), 71.61% (55 W) and 67.59% (26 W).The results showed that the hexahedral cone shaped artificial reef model had obvious attraction effects on P.cinctu under the three kinds of illumination, and the attraction effects reduced with the weakening of illumination.

Abstract:

The paper established a CFD simulation model of flow field inside the net cleaning machine, which was then analyzed by using CFD software of ANSYS-FLOTRAN. The distribution of flow velocity and that of flow pressure were obtained. The results provided important references for optimizing the structure of net cleaning machine.

Abstract:

In the current study, to establish the standard system for assessing the activity and quality of larval Penaeus monodon, whose tolerance to drying, starving, sharply-decreased salinity and formalin were investigated by methodologies of visualizing, microscopy and virus detection. The results showed that healthy postlarvae were featured with phototaxis and gregariousness; their body-surface was clean and the tissue was transparent; the stomach and intestine were full. The appropriate time for postlarvae to live without water was 15 minutes. After that, healthy postlarvae resumed vitality quickly while the sick ones were dead or narcose. The survival rate of postlarvae decreased with an extention of starvation time, with an increase of concentration of formalin and time, as well as with an abrupt drop of salinity. Healthy postlarvae could sustain about 30 minutes in 100~200 μL·L-1 formalin and the survival rate almost reached 100%. The appropriate range of salinity for postlarvae was 20~30, but they only sustained 1 hour in fresh water. Virus detection could avoid the outbreak of disease that might result from the postlarvae carrying with virus.

Abstract:

The effects of different densities of Bacillus substilis on water quality and on the immunity indicators of larval Penaeus vannamei were studied. The results demonstrated that B. substilis could significantly (P < 0.05) decrease the contents of COD, NH3-N and inhibit the production of NO2-N. With a density of 1.25×104 cfu·mL-1 of B.substilis, the average contents of COD, NH3-N and NO2-N of the treated groups decreased 65.30%, 59.70% and 88.64%, respectively. After 20-day cultivation, alkaline phosphatase (AKP), peroxidase (POD), phenoloxidase (PO), superoxide dismutase (SOD), the activity of anti-bacterial enzyme and bacteriolysis of Penaeus vannamei increased 3.67, 1.64, 0.45, 3.06, 2.57 and 1.14 times, respectively. Moreover, the survival rate of the treatment groups increased 10% and the weight gain increased 2.44 times when compared with the control group. Therefore, it showed that appropriate density of B.substilis could improve the water quality and the anti-disease ability of P.vannamei.

Abstract:

The research evaluated the effects of photosynthetic bacterium PS2 on the growth performance, digestive enzymes and serum nonspecific immune enzymes of cultured sea bass (Lates calarifer).Four levels of Rhodopseudomonas capsulate liquid product at concentration of 8×108 cfu·mL-1 were supplemented to a basal diet at 0.0 % (control group), 0.5% (group 1), 1.0 % (group 2) and 1.5 %(group 3), respectively. Diets were fed to the sea bass with initial body weight of(10.95±0.25)g for 50 days. The results showed that there was no significant difference in the weight gain, specific growth rate, survival rate and feed conversion ratio among all experimental groups (P>0.05).The liver protease, intestinal and stomach amylase of group 2 were significantly higher than those of the control group(P < 0.05).The intestinal protease of group 3 was significantly lower than that of group 2 (P < 0.05), but there was no significant difference between the experimental group and the control group(P>0.05).The pyloric caeca digestive enzymes of group 3 were significantly higher than those of the other groups (P < 0.05).There was no significant difference in serum AKP, POD and SOD among the groups (P>0.05).The results indicated that photosynthetic bacterium PS2 had no significant effects on the growth performance and nonspecific immune ability of the sea bass, but it could significantly promote the activity of digestive enzymes of pyloric caeca in group 3 and improve that of the liver protease, intestinal amylase and stomach amylase in group 2 (P < 0.05).

Abstract:

The complete sequences of mitochondrial Cyt b gene in Pagrus pagrus, Sparus macrocephalus, Acanthopagrus latus and Parargyrops edita in Zhoushan sea area were amplified, cloned and sequenced. The 1 141 bp Cyt b gene sequences of these four species were obtained. Compared with the same DNA fragment recorded in the GeneBank, the sequences of 1 141 bp DNA had 292 nucleotide variation sites, among which 186 parsimony informative sites were observed.Transitions were discovered to be more than transversions, and most of the base substitutions occurred at the third locus of the codon. The genetic distance among 4 Sparidae species ranged from 0.096 7 to 0.227 5. The shortest distance occurred between P.pagrus and P.edita, being 0.096 7, while the longest one between S.macrocephalus and A.latus, being 0.227 5. Moreover, the transition-transversion ratio of the sequence differentiation of 4 species ranged from 2.293 0 to 7.358 7. The NJ phylogenetic tree revealed that 25 species were divided into two clades, and obvious genetic divergence existed between fishes of Sparidae and the other fishes of Percoidea.

Abstract:

Effects of delayed initial feeding on the foraging, growth and survival of artificial bred larvae of ovate pompano (Trachinotus ovatus) were studied under the water temperature of (26.8±1.4)℃ and salinity of 28.2±0.8. The results showed that the larval mouth opened 3 days after hatching, and with the delayed initial feeding of 0, 1, 2, 3, 4 and 5 days, the feeding rate was 15%, 30%, 50%, 25%, 15% and 5%, respectively; the average consumption per larva within two hours was 0.4, 0.6, 1.3, 0.6, 0.3 and 0.1 prey, respectively. At day 6 of the delayed initial feeding, the feeding rate of all larvae was 0; there was no significant difference in the survival rate at the delayed initial feeding of day 0, day 1 and day 2 but the survivorship decreased abruptly while the delayed feeding lasted more than 3 days. The point of no return (PNR) occurred at 4 days after the larval mouth opened, which indicated that the optimum initial feeding time for the larvae was within 3 days after their mouths opened.

Abstract:

Packaged fresh tilapia fillets with different inflatable volume(V)- fish weight (m) ratios were stored at freezing-point; indices such as micro-organisms, TVB-N and TBA values were observed to study the effects of different inflatable ratios on the quality of fresh tilapia fillets.Experimental results showed that the ratio≥3 : 1 significantly inhibited the microbial growth of products (P < 0.05);the microbial number was still within the acceptable limit(106 cfu·g-1) at 25th day of storage.The gravy leakage rate of the modified atmosphere packaging(MAP) samples were higher than those in the control group, and the higher the inflatable ratio was, the more obvious the influence on the gravy leakage rate of products was.With the extension of storage time, TVB-N value in the control group was significantly higher than that of the packaging samples with the inflatable ratio≥3 : 1 after 4 days, and TVB-N value of samples with the inflatable ratio≥3 : 1 was still within the safety limit at 19th day, being about 19.30 mg·100 g-1.Different inflatable ratios had no obvious effects on the products′ pH value, and TBA value increased slowly throughout the storage period; the MAP samples did not differ significantly, but there was significant difference (P < 0.05)between the experimental group and the control group. To summarize, the inflatable ratio between 3 : 1 and 4 : 1, which did not significantly influence the quality of MAP samples during storage, could prolong the shelf life of fresh tilapia fillets significantly.

Abstract:

The changes in the sensory property, aerobic plate count (APC) and microbial flora of Pacific oyster (Crassostrea gigas) during storage at -3 ℃ were analyzed. The results showed that the sensory score decreased during storage, and got close to the sensory rejection point at 30th day. APC decreased slightly during the first 15 days, then increased afterwards, and the value was 4.1 lg cfu·g-1 at 60th day. All the strains isolated from raw oysters were identified to belong to 14 genera (families), among which Pseudomonas spp. (22%) and Vibrionaceae (20%) were dominant. During -3 ℃ storage, there were different changes in the proportion of each genus, among which Pseudomonas was dominant and its proportion increased from 22% to 54% at the end of storage.

Abstract:

The content and variation features of lead in marine organisms in Daya Bay were discussed in the paper. The results of the statistical analysis indicated that the lead content in the marine organisms in that sea area presented itself as a normal distribution, and the average value was(0.33±0.10)mg·kg-1. The lead content in the crustacean samples were obviously higher than that in cephalopod and fish samples. The research was conducted by following the four procedures of risk assessment.Therefore, the toxicity of lead was identified; its adverse effects on human health were described; the dietary exposure of lead in aquatic product intake was calculated using the Crude Point Estimate method, and finally the risk of lead was described. The results showed that the dietary exposure of the intake of the marine organisms captured from Daya Bay was within the reference dose.

Abstract:

Based on the survey data obtained by beam trawl and single-boat bottom trawl at Yellow River estuary in May 2007, a comparative study on the catch composition with two fishing gears was analyzed; indices of Sorensen similarity (SS), species richness (R), Shannon-Wiener diversity (H), Pielou evenness(J′) and index of relative importance (IRI) were calculated. The similarity of catch composition between beam trawl and bottom trawl was relatively small with a Sorensen similarity of 0.63. Indices R, H′ and J′ of beam trawl were 3.61, 2.28, 0.64 and those of bottom trawl were 3.55, 2.40, 0.72, respectively. The results showed that the diversity of bottom trawl was greater than that of beam trawl. It is suggested that the catch per unit effort of the two fishing gears was low with a poor selectivity, which would be greatly harmful to young individuals.

Review
Abstract:

There are abundant marine bioresources, such as purpleback flying squid (Sthenoteuthis oualaniensis)and yellowfin tuna (Thunnus albacares), in the deep-sea area of central and southern South China Sea. This paper introduced the status of tuna and squid fisheries and resources in South China Sea respectively.On this basis, the prospect for the development of relevant fisheries in China was discussed and it was proposed that the marine bioresources exploitation in South China Sea should focus on developing flying squid fisheries by using light falling net.

Abstract:

Streptococcus spp. is gram-positive and one of the major bacterial pathogens causing infectious diseases in human as well as in many vertebrates including swine, cattle and fish. Currently, the outbreak and prevalence of streptococcosis in fish, often occurring in various species of marine and freshwater fishes and mostly occurring in fishes of warm waters, have already been reported by many countries. There are more and more reports of tilapia infected with streptococcosis in China. In 2009, the outbreaks of streptococcosis were found in tilapia farms in southern China, including Guangdong, Guangxi, Fujian and Hainan provinces; the rates of streptococcal infectivity and mortality were 20%~50% and 50%~70%, respectively. Thus, streptococcosis has seriously hindered the development of tilapia aquaculture. This review summarized the reports on pathogeny, epidemiology, control and prevention of streptococcosis in tilapia, which would provide references for the prevention and control of streptococcosis in tilapia in the future.