Abstract:Selecting the right species to release for marine stock enhancement is not only the primary element of the practice, but also a precondition for ensuring positive effects. Selecting released species to restore ecosystems is the focus of future enhancement research. At present in China, the main species released for enhancement are those that can be mass cultured, with high economical value and low culture cost. These species are released in marine areas with short food chains and high resources. However, there are relatively few studies matching interspecific ecological relationships and the stability of community structure in marine waters targeted for stock enhancement, which is key to the practice. Herein, we used the abundance biomass comparison curve (ABC curve), to analyze the stability of both fish and nekton community structure in Laoshan Bay during the spring and summer of 2013-2015, and further discuss the selection of species for release. The results showed that:(1) fish community structure in Laoshan Bay in the spring and summer of 2013-2015 was relatively simple and unstable, and in a disturbed state; (2) nekton community structure was much more complex and stable than fish community structure during this time; (3) by comparing the annual and seasonal stability of community structure of both fish and nekton, we found that played an important role in maintaining the stability of the nekton community structure of Laoshan Bay in the spring, but played a vital role in maintaining stability in the summer. In conclusion, fish community structure in Laoshan Bay was relatively simple, but crabs and shrimp maintained the stability of the community structure of fishery resources. Crabs and shrimp should be given particular consideration when selecting species to release in this area. It was found that released in Laoshan Bay every spring increased the stability of nekton community structure during the summer in this area. The methods and results in this study can provide a scientific basis for the selection of released species.

Abstract:is one of the most economically important cultured shrimp species in the world. However, the frequent occurrence of various shrimp diseases has brought severe economic losses to the aquaculture industry. Moreover, the growth and development of are also affected by unstable aquaculture water. All of these restrict the healthy development of only relies on innate immunity to protect itself from external invasion. Therefore, it is very important to analyze its immune response and salinity adaptation mechanisms. Mitogen-activated protein kinase kinase 7 (MKK7) is a key regulator of the c-Jun N-terminal Kinase signaling pathway. It is involved in regulating cell response to a variety of extracellular stimuli. In this experiment, the full-length cDNA sequence of MKK7 ( was cloned by rapid amplification of cDNA ends (RACE) technology and the sequence was biologically analyzed. The full-length cDNA consisted of 2710 bp with a 1410 bp open reading frame, encoding 466 amino acids. In its conserved kinase domain, a serine/threonine protein kinase (S-TKc) region is a potential site for activation by upstream genes. The results of multiple sequence alignment and phylogenetic tree analysis showed that genes were clustered together and had the highest homology:99.14%. The quantitative real-time PCR (qRT-PCR) analysis shows that was ubiquitously expressed in all tested tissues. The highest expression level was in muscle tissue and the lowest expression was in stomach tissue. Following a bacterial injection experiment, the groups infected with had significantly higher expression in the hepatopancreas and gills than the control group (, expression in both tissues was significantly lower than the control group. After low salinity (17, 3) stress, the expression levels of in hepatopancreas and gill tissues was significantly up-regulated. After the increased significantly under low salinity stress, and the expression of in the downstream gene of the MAPK signaling pathway was inhibited. The results show that the JNK signal transduction pathway may play an important role in the immune defense and salinity stress tolerance of . It is hoped that more studies on the JNK signaling pathway will be conducted in order to better understand the innate molecular immune mechanisms of .

Abstract:In order to identify the most stable reference gene for the real-time quantitative PCR (qRT-PCR) analysis in Dabry's sturgeon (), seven commonly used reference genes, including beta actin (), glyceraldehyde 3-phosphate dehydrogenase (18S rRNA), succinate dehydrogenase complex subunit A () were selected as candidates. Their expression stability was evaluated in different adult tissues, and in the tissue of embryos, testes, and ovaries during different developmental stages. We used geNorm, NormFinder, BestKeeper, and RefFinder software to conduct the analyses. Results verified that optimal amplification efficiency was obtained from the primers of these candidate genes. In adult tissues, the stability of these reference genes was as follows:18S rRNA > ; during different developmental stages of embryos, the stability of these reference genes was:18S rRNA > ; during different developmental stages of testes, the stability of these reference genes was:18S rRNA > ; during different developmental stages of ovaries, the stability of these reference genes was: > . Overall, the most stable reference gene in adult tissue, embryos, and testes was to be most stable. This study provides a useful basis for future work examining gene expression in Dabry's sturgeon.

Abstract:In this paper, we analyzed the mitochondrial and nuclear genomes of Amur sturgeon () and Kaluga () to establish genetic markers that can be used for germplasm identification. In the D-Loop region of the mitochondrial genome, 119 samples from the three known sturgeon species as well as samples from 30 unknown sturgeon species were sequenced. The unknown species were identified by multiple sequence alignment, constructing NJ phylogenetic trees, and calculating genetic distance. In the nuclear genome, fifteen microsatellite markers were used to analyze differences in the genomes of the three known species. Two primers were obtained, Ls19 and SX226, which amplified specific bands in the three known species. In Amur sturgeon, the specific bands of Ls19 amplification products were 126 bp and 130 bp. In Siberian sturgeon, they were 139 bp and 143 bp, and in Kaluga, they were 124 bp and 127 bp. For SX226, the specific band of amplification products was 185 bp in Amur sturgeon. In Siberian sturgeon, the specific bands of SX226 amplification products were 260 bp, 273 bp and 283 bp,and in Kaluga, they were 180 bp and 182 bp. Based on the above results, the unknown sturgeon germplasm samples were identified as:17 , 2 Huso dauricus, and 8 . These results show that the Ls19 and SX226 microsatellite primers can be used in the molecular identification of germplasm from Amur sturgeon, Siberian sturgeon, Kaluga, and their hybrids.

Abstract:In aquaculture systems, a lack of water exchange, continuous input of food, and bacterial growth in culture tanks, can cause an increase in floc concentrations. Increased floc concentrations increase oxygen demand and clog the gills of cultured animals. Therefore, floc concentration is one of the most important management factors in a floc aquaculture system. The African catfish () is a candidate for biofloc aquaculture systems due to the ability to adapt to the adverse water conditions. No previous studies have investigated the effects of floc concentrations on African catfish cultured in biofloc aquaculture systems. The current study investigated the effect of different floc concentrations on the water quality, bacteria community compositions, nitrogen budget, and growth performance of juvenile African catfish in biofloc systems for 140 d. Two treatments were referred as low floc concentration (LF) or high floc concentration (HF), with an average concentration of 561.18 mg/L and 780.41 mg/L, respectively. The results suggested that there were no significant differences in average concentrations of total ammonia nitrogen (TAN), nitrite nitrogen (NO₂^--N), growth performance of the farmed fish, and nitrogen budget items between the treatments (-N) in HF (822.0 mg/L) was significantly higher than that of LF (623.33 mg/L), which suggested that the nitrification process was ongoing in the current aquaculture systems. BFT aquaculture systems always have high biomass, including cultured fish and microorganisms aggregated in bioflocs. The relative abundance of the top five phyla of bacteria did not differ significantly between the treatments (>0.05), however, a significant difference was observed at the genus level (<0.05). African catfish survival rates ranged from (91.11±1.53)% in LF, and (94.44±2.08)% in HF treatments. The food conversion ratio was (1.41±0.18) for LF and (1.27±0.26) for HF, and the specific growth rates were (2.13±0.04)%/d and (2.19±0.08)%/d, respectively. The efficiency of nitrogen use in food was 72.17% for LF and 71.34% for HF. It should be noted that the specific growth rates in the current study were lower than previous reports, perhaps owing to the uncontrolled water temperature and the extremely high suspended solids load. It is also worth noting that every time solids were removed, the rate of accumulation of TAN and NO₂^--N increased, and subsequently the NO₃^--N concentration decreased. The ratios of dissolved organic carbon (DOC) to total nitrogen (DOC/TN), or DOC to the sum of TAN, NO₂^--N, and NO₃^--N, in the two treatments were much lower than 20, which is the suggested value for biofloc aquaculture systems. This suggests that there is good control of TAN and NO₂^--N concentrations without any external organic carbon. The nitrification process was supposed to be ongoing in the current bioflocs systems. The results of the current study may lead to an effective water quality control system for culturing catfish, which may be applied in the commercial aquaculture industry.

Abstract:With increasing fish density in aquaculture systems, residual bait and a large amount of metabolic waste from over-feeding are accumulated in the water. These are then converted into ammonia nitrogen through ammonization. This, in turn enriches the water body, and does harm to the nervous, respiratory, and antioxidant systems of fish. The present study was conducted on Qi river crucian carp () larvae[body weight (15±2) g] to investigate the histological damage of excessive ammonia nitrogen (50 mg/L, 100 mg/L, 150 mg/L, 200 mg/L, 250 mg/L, and 300 mg/L) on brain, gill, liver, and kidney tissues. The results showed that the highest safe ammonia nitrogen concentration was 16.6 mg/L. Once the concentration of ammonia nitrogen was higher than the safe concentration, the structure of nerve fibers in brain tissue was destroyed, and the secretory and Sertoli cells showed different degrees of necrosis; the gill lamella showed different degrees of atrophy and aggregation, the base of gill filaments was congested and swollen, and the space between gill filaments was enlarged. Ultramicroscopic observation revealed that the sputum smear appeared atrophied, epithelial cells fell off, and secretion on the cell surface increased. As for the liver, the arrangement of hepatocytes around the central vein of liver tissue presented different degrees of disorder, the contours of hepatic lobules were blurred, and the nuclei showed different degrees of migration and dissolution. Ultramicroscopic observation showed that after 96 h of ammonia nitrogen stress, the distance between the hepatic lobules increased, the arrangement between hepatocytes was lost, the surface of cells was rough, and secretions increased. In the kidney, renal cysts were enlarged, lymphocytes exhibited infiltration and spreading, renal tubular lumen shrinkage was more serious, and glomerular necrosis occurred. The above results indicate that high concentrations of ammonia nitrogen cause different degrees of damage to the nerves, respiratory, and metabolic-related organs of Qi River crucian carp. Thus, the toxicity of ammonia nitrogen in high-density culture cannot be ignored. Therefore, we should strictly monitor the concentration of ammonia nitrogen in the culture water body and practice green and healthy cultivation.

Abstract:The purpose of this study was to investigate the effect of various sources of dietary lipids with vitamin E (VE) supplementation as feed additives on growth, flesh quality, and immunity in . A 3×2 factorial design with total 6 feed groups was implemented, comprising three different lipid sources[fish oil (FO), soybean oil (SO), and rapeseed oil (RO)] and two levels of dietary VE[200 mg/kg (200VE) and 600 mg/kg (600VE)]. The feeding trial was conducted in a cement pond inside a greenhouse. Prawns were fed thrice daily for 8 weeks. Results demonstrated that rate of weight gain and specific growth rate significantly increased in the SO and RO groups, compared to the FO group, while the feed coefficient significantly decreased (<0.05). VE had no significant effect on growth performance and feed utilization. We measured antioxidant parameters in lymph. Among prawns receiving the same amount of VE, both total anti-oxidative capacity (T-AOC) and superoxide dismutase (SOD) activity were significantly lower, while glutathione peroxidase (GPx) activity was significantly higher (<0.05) in the FO group than in the SO and RO groups. Malondialdehyde (MDA) content in the SO group was significantly lower (<0.05) than in the FO and RO groups. Among prawns receiving the same lipid source, supplementation with 600VE was found to significantly increase T-AOC activity in the FO group, GPX activity in the RO group, and SOD activity in both SO and RO groups (<0.05). Nevertheless, dietary VE level had no significant effect on MDA content of lymph. Physiological and biochemical indices of lymph, including aspartate aminotransferase (AST), total protein (TP), albumin (ALB) and triglycerides (TC) were significantly affected by diet type (<0.05); AST and ALB were significantly affected by ammonia nitrogen stress (<0.05). Further, dietary lipid sources and VE levels also had significant effects on flesh quality. Flesh was fresher and tasted better in the SO group; flesh in the RO group had less fishy odor, while flesh in the FO group had more color with less odor. At the 200 mg/kg VE level, flesh hardness, adhesiveness, cohesiveness, gumminess, chewiness, and resilience were significantly higher in the FO group compared to the SO and RO groups (<0.05); flesh cooking loss in the RO group was significantly higher than that in the other groups (<0.05). At the 600 mg/kg VE level, flesh tenderness and juiciness significantly increased, while there was no significant effect on flesh cooking loss and drip loss. Our results suggest that compared to fish oil, vegetable oils such as soybean oil and rapeseed oil are better sources of dietary lipids for . VE has a growth promoting and stress alleviating effect when added to feeds with fish oil as a single lipid source. In addition, both lipid source and VE level significantly affect the flesh quality.

Abstract:Herein we investigate the species composition and taxonomic diversity of coral reef ecosystems in a typical small-scale area in Qilian in the Xisha Islands. Based on fish survey data from the Nanhai Qilian Islands fishery in the 1970s and 2018-2019, we summarized the species composition of the Qilian Islands reef fish species using the taxonomic diversity index and the (family) diversity measure index. We found that the reef fish in the Qilian Islands area belonged to 175 species of 70 genera, 33 families, and 8 orders. Perciformes accounted for the largest percentage, at 81%. The average classification difference index (Δ⁺) is about 54.19, and the classification difference variation index () is about 112.35. We compared the community composition of Qilianyu fish to different regions, both at home and abroad. We found that the Δ⁺ of the Qilianyu fish is lower than the East China Sea shelf, Daya Bay, and Yubi Reef, but was higher than the Qibi Reef. The average grade-of-diversity index (-index) average was 3.09 and the normalized index average was 0.40. The results indicate that the classification of species in the fish community of Qilianyu is higher, and the genetic relationship is closer, than that of the East China Sea shelf, Daya Bay, and Zhubi Reef. The index values indicate that the species diversity of the reef fish in Qilianyu is relatively high, and that the distribution of families and genera was good historically. However, in 2018-2019, the diversities of the family and genus decreased significantly, so it is suggested to protect them in time.

Abstract:An investigation into the status of early-stage fish resources was carried out at the Jianli section, in the middle reaches of the Yangtze River, from May to July in 2018 and 2019. The survey focused on the changes in species composition of fish eggs and larvae, the amount of eggs and larvae, spawning site, and the ecological hydrology index following the experimental ecological operation of the Three Gorges Reservoir. About 49 species of fish eggs and larvae belonging to 14 families and 7 orders were identified, and among these fish, there were 26 species spawning drifting eggs. (44.9% of the total count) was shown to have an absolute advantage in the species composition of larvae, followed by sp. (12.5%). In 2018, it was estimated that the total runoff of fish eggs and larvae were 33.3×10⁸ ind and 324.2×10⁸ ind, respectively. In 2019, there were 35.9×10⁸ ind and 1140.7×10⁸ ind, respectively. The Jianli section has become an important spawning ground for , and other fish. Ecological regulation played an obvious role in promoting the natural reproduction of at the Jianli section. There was a positive correlation between the quantity of fish eggs and the time of flow increase, and a positive correlation between the quantity of fish eggs and the flow increase. When the duration of flow increase is four or more days, and the flow increase is 3500 m³/s or more, the spawning quantity could account for more than 8.4% of the annual survey total. We suggest continuing and optimizing the ecological flow scheduling to strengthen basic research on early-stage fish resources at the Jianli section.

Abstract:Fisheries stock assessments often rely on time series of abundance indices obtained from annual surveys. Thus, it is important to maintain the temporal continuity of such series when vessels have changed. This can be achieved by estimating conversion coefficients between the two vessels through an intercalibration experiment. This paper describes such an experiment conducted between the commercial trawler "zheshengyu10201-10243" (standard vessel) and the research vessel "zhongyuke211" (experimental vessel). Two analytical techniques were applied to compare trawl data and obtain fishing power correction factors for twelve major species and four species-group combinations caught by the two trawlers. Fishing power correction techniques included ratios of catch per unit effort (CPUE) and the Kappenman method. The results showed that 74 and 84 species were identified from the standard trawler and the experimental vessel, with catch rates range of (47.27-1836.72) kg/nmile², and (12.28-311.85) kg/nmile², respectively. The standard vessel had high catch rates of , The catch rate range were (1.17-1113.26) kg/nmile² and (0-565.39) kg/nmile², respectively. However, were the top two species caught by the experimental vessel, with catch rates range of (0-277.59) kg/nmile² and (0-125.24) kg/nmile², respectively. The trends of capture rate varied with depth showed differentiation between the standard vessel and the experimental vessel. Eight species/groups showed similar changes in capture rate by depth, including species-group, fish-group, Apogonichthys lineatus, . Five species/group showed the opposite trend in capture rate by depth, including crustaceans, Amblychaeturichthys hexanema and Harpadon nehereus showed mixed changes in catch rate at different depth stratum, which was related to the vertical expansion and the position of the net mouth. The ratio of mean CPUE and the Kappenman method estimated the total catch fishing power correction factor (FPC) to be 0.35 (95% confidence interval 0.24-0.61) and 0.43 (95% confidence interval 0.27-0.70), respectively. FPC values based on the ratio of mean CPUE ranged from a low of 0.03 for . The FPC was significantly different for five species-groups (Larimichthys polyactis and . It was necessary to correct the CPUE data by applying the estimated correction factor. The harvest of the standard vessel was dominated by near-bottom species, which represented its excellent performance in capturing economically important commercial species. However, the composition of the standard vessel's harvest was not strongly representative of the ecosystem. The experimental vessel was suitable for the investigation of shallow water areas. In deep water areas, due to insufficient vertical expansion and settlement of net mouth, it had difficulty capturing species reflecting the composition of the near-bottom ecosystem.

Abstract:The emergence and spread of antibiotic resistant bacteria brings risks to disease prevention and control efforts. Although the spread of antibiotic resistance has been a hot topic in recent research, information on antibiotic resistance in aquaculture is still lacking. A bacterial epidemic of was investigated in fish farms at Zhuhai, Guangdong province, China from April to December 2018, and a total of 96 strains of spp. were obtained. Among them, 87 strains were identified as strains were tested for resistance to 16 antibiotics and for their virulence in zebrafish using the KB method and challenge tests, respectively. The relationship of antibiotic resistance and virulence was assessed using Spearman correlation analysis. The results were as follows:(1) The percentage of strains resistant to each antibiotic was:Rifampin (98.85%), Madinomycin (96.55%), Erythromycin (95.40%), Penicillin (68.96%), Sulfamethoxazole (58.62%), Norepinephrine (28.73%), Amoxicillin (21.83%), Gentamicin (13.79%), Neomycin (10.34%), Furazolidone (3.45%), Norfloxacin (2.29%), Chloramphenicol (2.29%), Doxycycline (2.29%), Oxytetracycline (1.15%), Florfenicol (1.14%), and Enrofloxacin (0%). The antibiotic resistance spectrum revealed 32 total antibiotic resistant types existed in 87 strains. The Multiple Antibiotic Resistance Index (MARI) was 0.423, indicating that the strains were isolated in an environment with high exposure to antibiotics. (2) The virulence challenge tests showed that the lethality rate of 37 strains was > 80% in zebrafish, accounting for 42.52% of the total bacterial strains tested; the lethality rate of 39 strains was 30%-80% in zebrafish, accounting for 44.83% of the total bacterial strains tested; and the lethality rate of 11 strains to zebrafish was < 30%, accounting for 12.65% of the total bacterial strains tested. This demonstrates that is a high virulence strain. (3) Spearman correlation analysis showed that the virulence of <0.05), and negatively correlated with Enrofloxacin, Florfenicol (<0.01). Bacterial virulence may be related to antibiotic resistance and this relationship can be either negative or positive. We conclude that are highly toxic and multidrug resistant, and their virulence is negatively correlated with antibiotic resistance. This is presumably produced by the additional biological expenditure of bacteria to the acquisition of foreign DNA. Additional studies on this interaction mechanism may provide new data for the evolution of microorganisms and new ideas for bacterial disease control.