We isolated and identified the pathogen causing disease in largemouth bass (Micropterus salmoides) from a farm in Xinxiang, and investigated its pathogenicity. We combined the annotation of drug-resistant genes to analyze drug sensitivity results, and compared its genome structure, virulence factors and closely related strains to search for the common immune protective antigen functional genes. By the analyses of colony morphology and physicochemical properties, and based on the identification of isolated bacteria through 16S rRNA gene sequence alignment, we conducted hemolysis test, artificial regression infection test, drug sensitivity test, and whole genome sequencing analysis, then identified the isolated bacteria XXLX2 which was identified as Nocardia seriolae, without hemolysis circle on blood agar plates. The median lethal dose (LD₅₀) for largemouth bass was 1.49×10⁵ CFU·mL⁻¹ through regression infection tests, and the symptoms of infected bass were consistent with those of naturally diseased bass. The XXLX2 strain exhibited resistance to polymyxin B, erythromycin, and β-lactam antibiotics, and the results of drug resistance gene and drug sensitivity test were generally consistent. Through genome comparison analysis, the XXLX2 strain showed close phylogenetic relationship and good collinearity with three strains of N. seriolae from different sources, namely EM150506, NK201610020, and UTF1. There were certain differences in the comparison of virulence factors between the XXLX2 strain and the three strains of N. seriolae, but generally, they exhibited high conservation. Genomic annotation and comparative analysis of the XXLX2 strain provide basic data support for further exploration of the pathogenic mechanism of N. seriolae and research on genetically engineered vaccines.

Due to data limitation, most fisheries, most fisheries find it difficult to use traditional fisheries resource assessment methods to provide recommendations for fisheries management. As a result, data-limited assessment models have gained increasing attention, among which catch-maximum sustainable yield (CMSY) has become a widely used method internationally. However, studies indicate that CMSY is highly dependent on prior assumptions, and the specific impacts of different parameter priors on model outputs remain uncertain. To address this problem, we conducted a sensitivity analysis of CMSY by randomly selecting 200 fish and invertebrate populations from different sea areas from the RAM Legacy Stock Assessment Database. The model estimation results, including biomass trajectory, MSY, B_MSY, F_MSY, B/B_MSY and F/F_MSY were systematically analyzed to examine their variations by incrementally adjusting the upper and lower bounds of the intrinsic growth rate (r), and the biomass levels at the start, middle and end years (B_start/K, B_int/K, B_end/K). The results indicate that: 1) Biomass trajectory, B_MSY, and F_MSY were significantly influenced by the lower bound of r, while B/B_MSY and F/F_MSY were more sensitive to the upper bound of B_end/K. MSY was less affected by the prior settings of the parameters. 2) Taxonomic classification at the order level exhibited no significant influence on the sensitivity of the CMSY method. 3) Variations in parameter priors were observed to induce quadrant transitions in the population stock status depicted in the Kobe plot, among which the upper bound of B_end/K showed the most significant effect. This study reveals that the CMSY model exhibited high sensitivity to parameter prior settings. It is suggested that careful parameter configuration and result interpretation are essential when utilizing this model.

Hypsibarbus vernayi, an occasional species now, is an indigenous fish and economically important fish in the lower reaches of the Lancang River. In order to realize its artificial breeding and large-scale production of H. vernayi, and to provide guidance for the protection, development and utilization of the resources, we obtained its fertilized eggs by artificial oxytocin. Then we observed and recorded the developmental sequence and characteristics of the embryos and larvae. The results show that H. vernayi produced drifting eggs which were round and gray. The mature egg diameter was (0.7±0.1) mm, and the fertilized egg diameter was (3.5±0.1) mm after water absorption expansion. At the water temperature of 26–28 ℃, the embryo development process lasted for 16 h 45 min, and the accumulated temperature was 460.22 ℃·h, which experienced 7 stages including 33 periods (Blastoderm stage, cleavage stage, blastula stage, gastrula stage, neurula stage, closure of blastopore stage, organogenesis stage and hatching stage). The newly hatched larvae were transparent with a total length of (2.9±0.1) mm, and the heart was located in front of the yolk sac, where obvious heartbeat could be observed. Colorless and transparent blood flew without melanin deposition, and the yolk sac volume was small. The feeding started 36 h after the hatching. The yolk sac absorbed completely at 45^th hour. Since H. vernayi is vulnerable to starvation stress, it is needed to provide adequate opening bait to improve the seedling survival rate during larvae breeding.

Extreme waves and currents generated by the passage of typhoons have an important impact on the cage culture area. In order to assess the degree of hazard of typhoons with different paths and intensities on the large-scale aquaculture areas with in-cell nets in Maniao Bay, Hainan, we constructed a wave-current coupling model based on the Holland wind field model and the Delft 3D software, and the model was validated by using observational data. The typhoon paths were categorized into four types based on the paths and landfall locations of the historical typhoons, and "Rammasun", "Kompasu", "VONGFONG", and "Ted" were selected as the representative typhoons of the four types of paths. Seventy-two typhoon processes were reconstructed by translating and changing the typhoon intensity, and we simulated the process of change in the wave current field during the typhoon, obtained the statistics of different paths and intensity of the typhoon transit process of the maximum effective wave height and current velocity in the Maniao Bay aquaculture area, which were used as an assessment of the strength of the influence of the Maniao Bay nets aquaculture area, the strength of the impacts of the factors. Moreover, we analyzed the impacts of different paths and typhoon intensities on the net box aquaculture area, and proposed the range of warning paths during the transit of typhoons of different intensities. The results show that among the four types of typhoon paths, the first type of typhoon paths had the widest and greatest impacts on the net-pen aquaculture area, in which the maximum effective wave height in the net-pen aquaculture area under the R4 path was higher than 5.5 m, and the maximum current velocity was more than 1.5 m·s⁻¹ under the 'super typhoon' category, which severely affected the aquaculture area; the second and third types of typhoon paths had the greatest impacts on the net-pen aquaculture area. Most of the paths of Category II and III typhoons had less moderate impacts on the net-pen culture area; and the paths of Category IV typhoons had basically no impacts on the net-pen culture area under the intensity of each typhoon.

Intertidal zone is a transitional zone between marine and terrestrial ecosystems, which is sensitive to human activities. To explore the diversity of macrobenthos in the intertidal zone of Jiangshan Peninsula under different disturbances of human activity and evaluate its benthic ecological quality, we carried out a survey on macrobenthos in November 2023 (Autumn) and April 2024 (Spring) in two intertidal transects (Bailongwei and Bailangtan) in Jiangshan Peninsula, Beibu Gulf. We analyzed the species composition, density, biomass, dominant species and biodiversity of macrobenthos, and evaluated the ecological quality status of these two intertidal transects by using the AZTI Marine Biotic Index (AMBI) and multivariate AMBI (M-AMBI). The results showed that a total of 87 taxa of macrobenthos were collected, among which Mollusks were the most abundant (41 species), followed by Annelida (21 species), Arthropoda (19 species), and other groups (Six species). The average density, biomass and Shannon diversity index of macrobenthos in spring were lower than those in autumn. The results of the relative importance index (IRI) indicate that there was an obvious change in the dominant species of macrobenthos in the two intertidal transects across the season. The results of the AMBI and M-AMBI indexes show that although the disturbance at the Bailongwei transect is slightly higher than that at the Bailangtan transect, the overall ecological quality of both transects is generally at a good level.

To investigate the effects of photoperiod on gonadal development in largemouth bass (Micropterus salmoides), aiming to address issues such as reduced spawning and low hatching rates in broodstock caused by insufficient light during off-season reproduction. We randomly divided 450 individuals [Body mass of (420.8±30.5) g and gonadal development at Stage III] into three groups (Group 6L18D, 12L12D, 18L6D), and cultured them under photoperiods of 6, 12 and 18 h per day respectively; for the rest of the time the fish were was in darkness. Each group had three replicates with a total of 50 individuals including both males and females, and the experiment lasted 60 d. We evaluated the effects of photoperiod on their gonadal development and growth performance by measuring the body mass (Wt), hepatosomatic index (HSI), viscerasomatic index (VSI), gonadsomatic index (GSI), levels of sex steroid hormones, as well as observing the histological sections of gonads and analyzing the expression of genes related to gonadal development. The results show that although the Wt value in 18L6D group was higher than that in 12L12D and 6L18D groups without significant difference (p>0.05), its HSI, VSI and GSI values were significantly higher (p<0.05). The histological sections of gonads show that most of the testes and ovaries in 18L6D and 12L12D groups developed to Stage V, while those in 6L18D group were mostly at Stage IV, and a few developed to Stage V. The difference in the testosterone (T) concentration of male between 18L6D and 12L12D group was insignificant (p>0.05), but both were significantly higher than that in 6L18D group. The estradiol (E₂) concentration of female in 18L6D group was significantly higher than that in the other two groups. The expression levels of dmrt1 and gsdf genes in the testes of male and foxl2 and cyp19a1 genes in the ovaries of female in 18L6D group were significantly higher than those in the other two groups (p<0.05). In conclusion, increasing photoperiod within a suitable range helps promote the gonadal development of M. salmoides.

The lower reaches of the Jinsha River (Shuifu-Yibin section), a nursery habitat for various rare and endemic fish species of the Yangtze River, are one of the areas with dense construction of large hydrop projects. However, the fish biodiversity in this region is under severe threat. To assess the status of its fish resources, we had conducted ten surveys from 2021 to 2023 in three river sections: Anbian Town, Sankuashi and Baixi Town. The results show that a total of 69 fish species belonging to 8 orders, 20 families and 50 genera were collected, with the Cyiformes being the most abundant (48 species). There were 17 endemic fish species from the upper Yangtze River, 7 species of nationally protected wildlife, and 8 invasive species. The dominant species in the community included Coreius heterodon, Tachysurus vachelli, and Leiocassis crassilabris. Among the biodiversity indexes, only the Margalef richness index showed significant temporal and spatial differences (p<0.05). The ABC curve indicates that the fish community is in a state of moderate disturbance, but with a trend of increasing dominance of larger individuals. Cluster analysis shows that at a similarity level of 56.71%, the species from 2021 and 2022 were grouped together due to their similarities, while the ones in 2023 were more similar to historical records so they were grouped together. Compared with the results from 2021 to 2022, there had been an increase in fish species in the mainstream of the Jinsha River (Shuifu-Yibin section) in 2023. It is recommended that measures such as continuous fish stocking, controlling the invasion of non-native fish species, and strengthening scientific monitoring be implemented to further promote the recovery of fish populations in the Jinsha River and the Yangtze River.

In recent years, China has achieved remarkable achievement in deep-sea aquaculture of large yellow croaker (Larimichthys crocea), not only in terms of production, but also in terms of quality. Nevertheless, feeding operations are affected by natural calamities such as typhoons and powerful ocean currents. Therefore, to further improve the technological development of L. crocea culture in the deep sea, we used the fish with an initial body mass of (122.62±11.08) g and a body length of (17.9±1.04) cm as samples. Then we applied an underwater acoustic measurement system (Bandwidth of 20 Hz−20 kHz) to capture the underwater sound and observe the behavioral responses of the fish. The results indicate that the feeding sound of the fish could be distinctly classified into two types: pure swallowing and swallowing accompanied by chewing. Both swallowing and chewing produce sound mainly within the frequency of 6 Hz−13 kHz. Prior to feeding, the acoustic signals emitted by the fish were relatively sparse. However, when feeding began, the number of acoustic signals increased significantly. In a single feeding cycle, an individual fish exhibited 4−7 feeding behaviors, with pure swallowing being relatively infrequent. Swallowing was usually accompanied by 1−2 pulsed acoustic signals. Single pulses had a shorter duration, while double pulses had a longer one. The duration of these signals ranged from 0.05 to 0.25 sec, and the average sound pressure level generated was approximately (74.51±3.91) dB. When chewing, the fish most commonly produced 5−7 chews, with the chewing intensity gradually decreasing from (73.27±2.62) to (55.82±1.43) dB. Furthermore, as the number of feeding behaviors increased, the foraging duration of the fish also extended significantly, displaying a linear positive correlation.

The hydrolysis ozone which has strong bactericidal and purification effects has great potential for application in recirculating aquaculture system (RAS). To investigate the water purification effect of hydrolysis ozone, we constructed a RAS for perches (Lateolabrax japonicus) mainly using hydrolysis ozone treatment during a 120 days' aquaculture period. We measured the effects of different hydrolysis ozone aeration duration (30 min, 60 min, 90 min) on the water quality of the RAS. The results show that: 1) Perches grew well in a high-density aquaculture system, and their mass increased about 4.43 g every day with the final survival rate of 70.22%. No fish diseases were observed during the aquaculture process. 2) Hydrolysis ozone aeration could purify the RAS tail water by effectively removing ammonia nitrogen and nitrite, reducing the biochemical oxygen demand (COD) of tail water, and increasing dissolved oxygen (DO) and pH. Besides, it had less impacts on the increase of total nitrogen content (TN) and nitrate content. 3) The longer the ozone aeration time was, the better the removal effect of COD, ammonia nitrogen, and nitrite in the RAS would be. Under the 90-minute aeration treatment (Ozone mass concentration reached to 0.63 mg·L⁻¹), the removal rates of COD, NH₃-N, and ${\mathrm{NO}}_2^{\text{−}}$ reached 44.32%, 36.85%, and 79.27%, respectively. Therefore, it is concluded that hydrolysis ozone has a good effect on improving the density of RAS, effectively controlling the occurrence of fish diseases and purifying the tail water of RAS.

Aquaculture vessels are a new way to expand deep-sea aquaculture. How to improve the utilization efficiency of aquaculture tanks to ensure the best growth conditions for fish in aquaculture tanks and the efficient discharge of particulate matter from the tanks will affect the productivity of aquaculture and the profitability of aquaculture vessels. In order to investigate the influence of the diameter to depth ratio of the tanks on the flow field characteristics and the drag coefficient of the tanks, as well as to provide a reference for the structural design and optimization of aquaculture tanks on aquaculture vessels, we carried out an experiment of the flow field characteristics of the tanks of aquaculture platform under mooring condition by using a real-ship test method. We evaluated the influence of the diameter to depth ratio on the fishability and energy loss of the tanks by studying the flow velocity, drag coefficient and the uniformity index of flow field, etc. The experimental results show that the flow velocity in the tanks was positively correlated with the diameter to depth ratio: when the diameter to depth ratio was less than 1.6:1, the reduction of the diameter to depth ratio led to a significant reduction of the flow velocity in the tanks, and the tanks with a diameter to depth ratio of 1.8∶1–2.0∶1 possessed better flow characteristics, including higher flow velocity, flow uniformity and lower drag coefficient; a diameter to depth ratio of 1.8∶1 for the aquaculture tanks met the requirements of flow field and economic efficiency in the tanks, and this ratio should be considered as a priority in the aquaculture system of aquaculture vessels.

Regarding the cumbersome finite element modeling problem caused by the complex structure and diverse loads of deep-sea floating raft aquaculture cages, we applied an efficient finite element analysis and designed a structural optimization method. Taking a 40-meter-diameter deep-sea raft-type aquaculture cage as an example, we achieved parametric calculation and application of loads including wind, wave, and current through systematic algorithm development and programming. The work implemented functions such as node/element definition and real-time optimization parameter updates, while conducting secondary development based on ANSYS software. This approach enabled efficient modeling and reconstruction of the cage's finite element model. On the basis of the efficient finite element modeling, the structural optimization based on the genetic algorithm was realized, and the robustness of the optimization algorithm was enhanced by introducing the power variation function. The results show that under the condition of consistent structural strength, the optimized cage effectively reduced the mass by 17.98%. The method in this paper can provide a reference for the design and structural optimization of deep-sea floating raft aquaculture cages.

Aquatic plant plays a crucial role in controlling the ecological conditions of crayfish (Procambarus clarkii) aquaculture. In order to clarify the path of different types of aquatic plants affecting crayfish culture performance, we examined the impacts of Hydrilla verticillata and Alternanthera philoxeroides on the growth and development performance of crayfish, and determined the intestinal natural diet composition by using high-throughput sequencing technology. H. verticillata and A. philoxeroides exhibited substantial water purifying properties, significantly increasing the dissolved oxygen (p<0.05), while decreasing the phosphate content, nitrite, ammonia and nitrate nitrogen contents (p<0.05). The growth indexes of H. verticillata and A. philoxeroides groups were significantly higher than those of the control group (p<0.05), whereas the former two groups showed no significant differences (p>0.05). The temperature, dissolved oxygen and pH had a greater effect on the growth performance of crayfish in H. verticillata and A. philoxeroides groups, while the nitrite and ammonia nitrogen had a stronger effect on the control group. The phytoplankton in the control group had significantly higher density and biomass than the aquatic plant groups (p<0.05), while A. philoxeroides group had a significantly higher abundance and diversity of plankton communities than the control group (p<0.05). The results of constrained principal axis analysis (db-RDA) reveal that the food content in crayfish intestines varied significantly among the groups (p<0.01). In summary, H. verticillata and A. philoxeroides can improve the aquaculture environment, promote the growth performance of crayfish, and enrich its food composition.

To investigate the behavioral characteristics to flow velocity, we measured the swimming behaviors of juvenile Lateolabrax maculatus of different individuals (1, 2, 4, 6 and 8) at various flow velocities (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 BL·s⁻¹; BL: Body length) by using swimming ability test tank. When the flow velocity reached 4.5 BL·s⁻¹, the group movement speed (Gc) of fish schooling was significantly lower than that of single fish (p<0.05). With an increase in the flow velocity, the inter-individual distance (IID) (Reflects the cohesion of fish swarm) first decreased and then increased in each group, and valley values were observed when the flow velocity reached 3.5–4.5 BL·s⁻¹. Besides, the flow velocity corresponding to the above IID valley increased with the expansion of fish population. Besides, the trend of swimming speed synchrony (S_V) (Reflects the coordination of fish population) was completely opposite with that of IID, and the flow velocity corresponding to the S_V peak also increased with the fish schooling expansion. When the flow velocity reached 1.0 BL·s⁻¹, the tail beat frequency (TBF) of single fish was significantly higher than that of other groups at the same flow velocity (p<0.05). With the increase of flow velocity, the proportion of diamond lattice displayed in fish schooling first decreased and then increased, which was opposite to the phalanx lattice pattern. However, the pattern of diamond lattice was always dominant in each group at different flow velocities. In conclusion, with the increase of flow velocity, the cohesion and coordination of L. maculatus schooling first increase and then decrease. The expansion of the fish population is conducive to improving its cohesion and coordination, and the fish mainly adopts a diamond lattice pattern to reduce swimming energy consumption.

Low-temperature acclimation is critical for live fish transportation to reduce injuries and mortality by inducing the fish into semi-hibernate state. Thus, we investigated the suitable holding temperature for largemouth bass (Micropterus salmoides) transportation, focusing on the effect of water temperature on its muscle tissue, serum biochemical indicators, antioxidant enzyme activities and respiratory function. The results show that the respiratory rate of M. salmoides gradually decreased as temperature descended. Significant differences were observed in the muscle tissue, pH, serum biochemical indicators, and antioxidant capacity between temperatures (15 ℃ and 20 ℃) and lower temperatures (9 ℃ and 12 ℃) (p<0.05) during holding of 48-hour. M. salmoides exposed semi-hibernate state at 12 ℃, which led to a significant lower quality of total ammonia nitrogen (TAN) accumulation in the water (p<0.05) and a slower TAN increase rate. In the 12 ℃ group, the serum glucose (GLU) and lactate dehydrogenase (LDH) concentrations decreased significantly, while the total antioxidant capacity increased, with no significant changes on other indicators (p>0.05), and the blood cells in the gill tissue arranged orderly, with gill filaments showing no obvious deformation. The findings indicate that 12 ℃ holding not only effectively maintains water quality, but also effectively preserves the physiological functions and antioxidant capacity of fish, thereby reducing damage caused by oxidative stress reactions. Therefore, it is recommended to control the temperature of the water body at around 12 ° C during the actual holding and circulation process.

Tetrodotoxin (TTX) is a potent marine toxin, found in a great variety of marine and some terrestrial species. In order to explore the potential bacterial sources of tetrodotoxin (TTX) in Nassarius semiplicatus, we collected its TTX and analogues from Fujian and analyzed them by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Besides, we compared the microbial communities of TTX-bearing and non-TTX-bearing by using high-throughput sequencing technology. The results show that the content of TTX in TTX-bearing N. semiplicatus (LTN) were 402~644 μg·kg⁻¹. TrideoxyTTX, dideoxyTTX and deoxyTTX were detected. TTX and other analogues were not detected in non-TTX-bearing N. semiplicatus (NTN) except dideoxyTTX. The results of high-throughput sequencing show that the community richness of LTN was significantly higher than that of NTN (p<0.05). The microbial communities of LTN and NTN were dominated by Proteobacteria. TTX-producing bacteria, including Vibrio, Pseudoalteromonas and Psychrobacter, were the dominant bacteria in LTN, while Pseudoalteromonas and Shewanella in NTN. The significant difference analysis shows that the relative abundance of 17 differential genera in LTN, including Vibrio and Psychrobacter, etc., were significantly higher than that of NTN (p<0.05). The KEGG functional composition of the intestinal flora of LTN and NTN were similar. The main metabolic pathways were amino acid metabolism, carbohydrate metabolism and so on. The results show that TTX-producing bacteria can exist in both LTN and NTN; Vibrio and Psychrobacteraremore enriched in LTN. These TTX-producing bacteria may be related to the biosynthesis of TTX analogues and precursors in N. semiplicatus.

The hydrodynamic load on netting has a significant impact on the force and motion of aquaculture platform. To determine the hydrodynamic load on netting of different materials and structural forms, by studying the structural and material characteristics of netting, we designed the standardized calculation methods for the hydrodynamic load factors on fiber netting and metal netting. For fiber netting, we set a formula for calculating the solidity of netting applicable to different mesh shapes. For metal netting, we set a formula for calculating the hydrodynamic load factors equivalent of netting applicable to different mesh shapes. Besides, we analyzed the impact of mesh shape on the hydrodynamic load factors of netting. The calculation results show that when the mesh edge length was the same, for knotless fiber netting, the hexagonal netting experienced the least hydrodynamic load factors. For metal netting, the rectangular welded netting experienced the least hydrodynamic load factors. The findings provide a reference for the selection of netting types and hydrodynamic load calculations for fishery platform.

To understand the characteristics of gas-liquid two-phase flow in the speece cone and improve its oxygenation performance, taking the speece cone in an oxygenation system of large-scale aquaculture vessel cabin as the subject, we carried out a two-dimensional transient numerical simulation of gas-liquid two-phase flow in the speece cone under different conditions (Gas inlet method, taper and aperture size) based on the Euler-Euler model, analyzed the gas volume fraction distribution, the internal flow field pressure and the velocity distribution, explored the flow law of gas-liquid two-phase in the speece cone, and determined the key structural parameters influencing the aeration and oxygen dissolving performance of the speece cone. According to the results, under a given air inlet flow, when the gas inlet was consistent with the water inlet from speece cone, the mixing degree of gas and water was high. The experimental verification shows that the speece cone with top inlet had the best dissolved oxygen performance compared with the other two methods. When the speece cone had the same volume, changes in the taper of the speece cone led to gas-liquid two-phase changes: a smaller taper, a higher speece cone, and longer motion path and mixing time of oxygen in the speece cone, favoring full oxygen dissolution. By the same gas inlet method, the gas-liquid two-phase distribution was similar in the speece cone. The volume fraction of the speece cone outlet gas increased with decreasing air inlet aperture, and when the air inlet aperture was reduced to d =10 mm, the gas and liquid were best mixed in the speece cone.