Abstract:Based on 216 samples (120 silver pomfret samples, 51 prey organism samples, and 45 fish samples) obtained from three bottom trawl surveys in the Bohai Sea from September to November 2017, the stable isotope ratios of samples were determined by carbon and nitrogen stable isotope techniques. The contribution ratios of the various types of diet were calculated, and the characteristics of feeding habit, trophic level, niche breadth, and niche overlap with fork length were evaluated. The accuracy of the study in terms of the feeding ecology of silver pomfret based on the stable isotope method was confirmed by a comparative study. The results showed that:(1) the δ¹³C value of silver pomfret was -19.50‰ to -14.85‰, and the average value was -17.18‰, which was not significantly correlated with fork length (N value of silver pomfret was 11.55‰-14.77‰, with an average of 13.30‰. The correlation with the fork length was highly significant, whereas the correlation intensity was weak (<0.01). (2) Stable isotope analysis (Stable Isotope Analysis in R) based on Bayesian mixing models was applied to calculate the contribution rate of each prey item; the results indicated that the silver pomfret is an omnivore, and its main prey is benthic shrimps, with a contribution rate of 11.52%-57.49% and the average contribution rate was 35.03%. This was followed by , with a contribution rate of 13.52%-42.82% and an average contribution rate of 27.87%. The contribution of other prey items was from squid , phytoplankton, and zooplankton, and their rates were 6.41%-42.57%, 0-21.33%, and 0-16.21%, respectively. The average contribution rate was 23.29%, 8.08%, and 5.77%. (3) There was some change in the food composition of silver pomfret as the length of the fork increased. The nutrient niche breadth of sliver pomfret tended to increase and then decrease with the change in fork length, and the niche breadth of the 90-109 mm fork length group was maximal. However, the nutrient niches of each fork group were similar, and there were more overlaps in the niche. (4) The trophic level of Bohai silver pomfret was 2.84-3.79; the average trophic level was 3.35, and the trophic level increased with increasing fork length. (5) The MDS plot showed that the similarity of the δ¹³C and δ15N value of silver pomfret and red nose anchovy 15N value of gizzard-shad C value and δ¹⁵N value of scaled sardine and gobiid fishes were similar. In this study, comprehensive information on the trophic level and feeding habits of silver pomfret was obtained from stable isotope analysis, which was significant for building an end-to-end food web and for the study of its dynamics in the Bohai sea.

Abstract:Six Schizothoracinae fishes, which are important economic indigenous fishes, form the dominant group in the middle Yarlung Zangbo River of Tibet. During the course of evolution, Schizothoracinae fishes have developed unique characteristics, including a slow growth rate, long life cycle, late sexual maturity, and low reproductive capacity. Their germplasm resources are fragile and sensitive to human interference. Once destroyed, population resources will be difficult to recover. In recent years, there has been a serious decline in Schizothoracinae fish resources due to the impact of human activities and environmental changes; their distribution has been reduced, and their population resources have been destroyed. There is an urgent need to protect the Schizothoracinae fish resources. Therefore, it is necessary to quantitatively assess the priority conservation of Schizothoracinae fishes in the middle Yarlung Zangbo River. Based on fishery resources survey data collected during the spring (April-May) of 2015 and 2017 in the middle reaches of the Yarlung Zangbo River, combined with relevant literature and field survey data and information accessed for recent years, we used five evaluation indexes of value and rareness, species value, and human interference. Then, we evaluated the resource status and endangered status of six Schizothoracinae fishes and obtained the priority conservation grade of these fish according to the scoring criterion and the comprehensive evaluation value was the first priority conservation fish; was listed as the second priority conservation fish; were the joint third priority conservation fish; and were the joint fourth priority conservation fish. These evaluation and classification results are consistent with the real-life situation, which reflects the priority conservation order of six Schizothoracinae fishes. This study provides suggestions and reference for the scientific protection and management of Schizothoracinae fish resources in the middle reaches of the Yarlung Zangbo River.

Abstract:The offshore water of southern Zhejiang is an important breeding and fattening ground for small yellow croaker . In this study, based on bottom trawl surveys, 2023 samples of small yellow croaker with a body length of 3.0-21.5 cm were collected in February, May, August, and November 2016 in the offshore water of southern Zhejiang. Based on the length and weight data of these samples, the dominant body length was 11.0-15.0 cm, accounting for 69.9% of samples, and the dominant weight was 20.0-50.0 g, accounting for 68.26% of samples. The age ranged from 0 to 4⁺ years. Based on 2019 sample data, the length-weight relationship was fitted by a power function, which could be described as was 2.8635, meaning that presented a negative allometric growth pattern. The Von Bertalanffy growth parameters were estimated using FiSAT Ⅱ electronic length frequency analysis I. The asymptotic length a) was estimated as -0.37 a. The growth coefficient was 0.78 per year, indicating the fast growth rate of this small demersal species in the offshore water of southern Zhejiang. The total mortality coefficient was calculated using a length-converted catch curve as 4.432, and the natural mortality coefficient was estimated as 1.343 by the Pauly empirical formula. Therefore, fishing mortality coefficient equaled 0.697, demonstrating that the stock was subjected to overfishing. The catch curve also determined that the current first capture was 13.11 cm, corresponding to an age of 0.743, which was lower than both the critical age (0.886) and the turning point age (0.931); this indicates that the main fishing objectives were juvenile and included the recruitment group of small yellow croaker. The Beverton-Holt (B-H) model was used to evaluate the yield per recruitment for . Based on the dynamic B-H model, the current yield per recruitment (YPR) value was 15.279 g/ind. If ), the corresponding YPR was 17.061 g/ind, with an increase of 11.66% over the current YPR. When was increased from 13.11 cm to 17 cm, the estimates for YPR_max would increase from 15.279 g/ind to 18.766 g/ind, an increase of 22.82% over the current YPR. Thus, it would be better to increase . In conclusion, these data indicate that the current stock of is over-exploited; hence, to protect the spawning stock and maintain the population in a sustainable manner, we suggest increasing the length of the first capture to 15 cm, which will satisfy full growth and correspond to the optimal yield area of under the present fishing pressure.

Abstract:Ecological niche refers to the sum of the physical space, functional status, and environmental requirements occupied by species in a community. The ecological niche plays an important role in studies on community structure, interspecific relationships, and biodiversity. Based on data collected from the bottom trawl surveys in 2013-2014 in the Yellow River estuary, the spatio-temporal niche width and overlap for 12 fish species were examined using the mean crowding, niche width, and niche overlap indices. The temporal niche width indices for main fish species ranged from 0 to 1.53, which were relatively high for and relatively low for . The spatial niche breadth of the main fish species varied with season, and it was high in winter for Liza haematocheila and low in summer for . The temporal niche overlap indices among main fish species ranged between 0 and 1, and 11 species pairs reached significant ecological niche overlap. Thirty-two species pairs had low temporal overlap, occupying 46.48% of the total species pairs. This showed that the main fish species were not similarly distributed in time. Clear seasonal changes in the spatial niche overlap indices were observed for fish pairs. The spatial niche overlap indices between ranged from 0.22 to 0.86, and were high in summer and autumn and low in winter. The mean spatial niche overlap indices for all species pairs varied between seasons, they were highest in autumn at 0.17, followed by summer (0.11-0.14) and spring (0.07-0.13) and were the lowest in winter (0.07). Cluster analysis showed that all the species pairs could be divided into five groups in terms of spatial niche overlap, with relatively high niche overlap among species pairs in each group. Niche breadth and overlap for fish species was strongly related to species abundance, spatial distribution, ecological habit, and habitat conditions, which revealed the different abilities of species to effectively utilize the environmental resources in the Yellow River estuary.

Abstract:Based on data from the macrozoobenthos resource survey along Yanpu Bay in October 2014 (autumn) and October 2016 (autumn), variation in the ecological niche and functional groups following planting of were studied via niche breadth, niche overlap, functional group classification, and redundancy analysis (RDA). The results showed that the proportions of the wild niche and middle niche species increased after planting whereas that of the narrow niche species decreased. The species pair comprising (0.94) presented the highest niche overlap before planting, whereas those of Assiminea violacea and (0.99) were highest after planting. Compared with the diversity index of the functional groups before planting, the diversity index of the functional groups in high and middle tidal zones was increased whereas that in low tidal zones was reduced after planting. Densities of the planktophagous group (Pl), phytophagous group (Ph), and omnivorous group (Om) increased whereas that of the carnivorous group (Ca) decreased slightly compared with the year before planting. There were significant differences (<0.05) between the high and low tide zones, as well as the middle and low tide zones after planting; however, the relationships between each pair of intertidal zones were not significantly different (>0.05) before planting. The RDA concluded that the factors with greater effects in macrozoobenthos communities changed from lead, cadmium, and petroleum before planting to zinc, cadmium, and arsenic after planting. In summary, planting along Yanpu Bay had a positive effect on the overall improvement of the ecological niche and functional groups of macrozoobenthos.

Abstract:In recent years, biofloc technology (BFT) has become an important water-saving and emission-reducing aquaculture model in aquaculture development. However, in high-density farming ponds, the concentrations of ammonia and nitrite are often much higher than established standards. High ammonia and nitrite concentrations are harmful in aquaculture, where they increase the stress experienced by shrimp, resulting in disease outbreaks. The removal of ammonia and nitrite is an effective method of reducing water pollution resulting from residual food and feces. The Y2 strain, which can efficiently remove ammonia and nitrite, was isolated from the culture water of . Experiments investigating the physiology-biochemistry of this strain and the similarity of 16S rRNA gene sequences have been conducted. The safety of Y2 was evaluated by an immersion infection and antimicrobial susceptibility test. The fermentation conditions, including temperature, pH, and salinity, were optimized, and dynamic changes between bacterial growth and the concentration of pollutants in water were investigated. Water quality, the amount of bioflocs, the number of pathogenic bacteria, and the growth and survival rates of shrimps were monitored through a 28-day culture experiment. The Y2 strain was preliminarily identified as , based on physiological and biochemical characteristics and 16S rRNA sequence analysis. The strain was resistant to oxacillin and clindamycin. Optimum fermentation of the Y2 strain was observed under conditions of 30℃, pH 7.0, and 2% salinity. The 48 h half-lethal concentration of the strain to Artemia was higher than that of cfu/mL, and this strain was nontoxic to cultured animals. The Y2 strain continuously removed ammonia and nitrite from aquaculture water. It inhibited the growth of vibrios, increased the survival and growth rates of shrimps, and was able to survive in water for a long period of time. Therefore, the Y2 strain has high potential as a probiotic for aquaculture and may be used as the key bacterium to regulate water quality in bioflocs culture systems.

Abstract:To determine the taxonomic status, characteristics, and histopathology of nematodes infecting the intraperitoneal tissues and organs of Bleeker, PCR analysis were used to evaluate 18S rDNA and ITS rDNA sequences and microscopic observations were used to evaluate nematode morphology and histopathology. Nematodes were identified as the fourth-stage larvae of and their ITS rDNA sequences were confirmed. Six spinous papilla and six papillary papilla were identified in the cephalic extremity and caudal plaques in the posterior of . In addition, data were supplemented, and new characteristics of morphological structures, including lateral plaques with grooves, were identified. Their body muscles were of the polymyarian type according to the number of muscle cells and their characteristics at one end of the body, which stretched into the coelom. The esophagus consisted of a dorsal gland, ventral glands, and a three-radiate esophageal lumen. The intestine was more cell type according to the number of monolayer columnar epithelial cells in the intestine. The outer layers of the ovary, oviduct, testis, and spermaduct were composed of connective tissue mainly with fibrocytes. Histopathological observations revealed that some nematodes infected the liver, mesentery, and spleen, with the formation of cysts in the abdominal cavity of fish. The main inflammatory responses were the formation of cysts, which were mainly composed of fibrocytes, blood vessels, and many infiltrated eosinophilic leukocytes. The cyst underwent formation, wall thickening, enlargement, cell wall necrosis, and rupture in the late stage. Severely infected livers appeared congested, with cell necrosis and hemosiderosis. The spleen presented ischemia and hemosiderosis. Secretory granules of pancreatic cells in the mesentery were increased. Thus, infection with the fourth-stage larvae of induces different degrees of histopathological changes in the internal organs of host fish.

Abstract:Currently, the strategies for prevention and treatment of bacterial diseases in fish are dominated by the use of drugs such as antibiotics. However, the overuse of antibiotics will continue to cause the development of resistant strains. This leads to ineffective treatment with antibiotics during disease breakouts in aquatic animals. Therefore, research into the development of antibiotics that are low in toxicity and not susceptible to resistance has become an urgent task. Increasing studies on Chinese herbal medicines and their extracts have been performed for the prevention and treatment of bacterial diseases in aquaculture. Fraxetin is a natural simple coumarin compound with good antibacterial effects and inhibitory effects against . To provide evidence for the prevention and control of aquaculture diseases, we studied the antibacterial effect of fraxetin on and on the virulence of pathogenic bacteria. Additionally, the minimum inhibitory concentration (MIC), growth curve, biofilm, lipase activity, motility, protease activity, and hemolysis were evaluated. We determined the MIC using the micro-broth method. The growth curve was determined by OD₆₀₀; biofilm formation was detected by crystal violet staining; bacterial liquid was spotted onto solid medium to determine lipase activity and motility; and the co-culture supernatant was collected to determine protease activity and hemolytic activity. The results showed that fraxetin had significantly inhibited was clear and transparent after 24 h, when the concentration of fraxetin was 128 μg/mL and 256 μg/mL. Therefore, the MIC was 128 μg/mL. The inhibitory effect of fraxetin on was concentration-dependent. Fraxetin significantly inhibited the growth of <0.05). At 8 μg/mL, fraxetin did not significantly inhibit the growth of >0.05). The logarithmic growth phase was apparently delayed (<0.05), and the concentration of bacterial solution in the plateau was significantly lower than that in the control group, when the concentration of fraxetin was more than 32 μg/mL. When the fraxetin concentration exceeded 16 μg/mL, <0.05). At 8 μg/mL, fraxetin reduced the lipase activity of <0.05). It had a non-significant effect on the motility and hemolytic activity of >0.05); however, fraxetin at these concentrations could decrease the protease activity of <0.05). Fraxetin presented antibacterial activity against A. hydrophila virulence was limited at non-bacterial concentrations. The prevention and control of by low concentrations of fraxetin requires further study; as the drug affects the pathogenic microorganisms as well as the host, considering the complexity of the effects of Chinese herbal medicines in the body.

Abstract:Viruses rely on host cellular metabolism for energy and macromolecule synthesis during replication. Therefore, there is a close relationship between viral replication and cellular metabolism. rhabdovirus (SCRV) causes significant economic losses in the Chinese perch () industry. Thus, it is important to address the interaction between SCRV replication and host cells to prevent and control SCRV. However, little is known about the relationship between SCRV replication and cellular metabolism. In addition, glutamine is an abundant amino acid necessary for energy generation and macromolecule synthesis in cells. Glutamine is also essential for the infection and replication of some viruses. Glutaminolysis and reductive glutamine metabolism (RGM) are the main pathways of glutamine metabolism. Particularly, the RGM pathway plays an important role in tumor cells. However, the metabolic pathway of glutamine involved in viral replication remains largely uncharacterized. To clarify the interaction between SCRV replication and RGM, we analyzed the expression of key enzymes in the RGM pathway in Chinese perch brain (CPB) cells following infection with SCRV, using quantitative real-time PCR (qRT-PCR) and western blotting. Our results showed that SCRV replication was decreased in CPB cells cultured in a glutamine-depleted medium, indicating that glutamine is required for efficient SCRV replication. In addition, SCRV infection promoted the expression of key enzymes involved in the RGM pathway in CPB cells, particularly the expression of isocitrate dehydrogenase 2 (IDH2), indicating that RGM in CPB cells is altered during SCRV infection. SCRV proliferation was also inhibited in CPB cells cultured in the presence of bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (a glutaminase inhibitor), (-)-epigallocatechin monogallate (a glutamate dehydrogenase inhibitor), 5-(tetradecyloxy)-2-furoic acid (an acetyl-CoA carboxylase inhibitor), or 4-methylene-2-octyl-5-oxotetrahydrofuran-3-carboxylic acid (a fatty acid synthase inhibitor), suggesting that the RGM pathway is beneficial for SCRV replication and proliferation. Furthermore, downregulation of the IDH2 gene, the product of which converts α-ketoglutarate (α-KG) to citrate, significantly inhibited the yield of SCRV and the expression of the SCRV structural protein. Conversely, overexpression of the IDH2 gene significantly increased the yield of SCRV and the expression of SCRV structural protein, indicating that IDH2 plays an important role in SCRV replication and proliferation. These results indicated that SCRV infection induces RGM to accommodate the biosynthetic and energy needs required for its efficient replication and proliferation. These findings provide new insights into viral pathogenesis and antiviral treatment strategies.

Abstract:Common carp (), the earliest farmed fish in the world, is one of the most important and economically significant species in freshwater aquaculture in China. In recent years, carp edema virus (CEV) disease, a newly emerged infectious disease in common carp, has been discovered in many countries, threatening the healthy development of common carp farming. Due to a lack of CEV-sensitive cell lines, detection of CEV relies on methods that use electron microscopy and polymerase chain reaction (PCR); however, these methods are not used universally for clinical diagnosis because they require expensive equipment and a long response time. Therefore, there is an urgent need to establish a simple, accurate, and rapid diagnostic method to detect CEV. Loop-mediated isothermal amplification (LAMP) is a novel amplification technique used to produce DNA copies within 1 h. Furthermore, the results can be judged based on turbidity or by the addition of SYBR Green I to the reaction products and observation of color change within the reaction system. LAMP technology has played an important role in human medicine, animal medicine, and food safety, and has gradually been developed for industrialization and commercialization. In this study, two pairs of specific primers were designed based on the conserved sequence of the gene encoding the CEV nucleus protein, , and a recombinant plasmid was constructed for use as a standard template for amplification. Then, a LAMP detection method for CEV was established after optimizing the reaction conditions. The optimal LAMP reaction system for CEV detection included F3/B3 0.2 μmol/L, FIP/BIP 1.2 μmol/L, betaine 0.7 mol/L, Mg²⁺ 8.0 mmol/L, and dNTPs 1.2 mmol/L and was performed at 62℃ for 60 min. The amplified products included a ladder band on agarose electrophoresis and green products, which were observed directly by the addition of SYBR Green I. The sensitivity of the detection method for CEV was 10 copies/μL, which is 100-fold higher than the traditional PCR method. Moreover, CEV-LAMP was specific for detecting CEV without cross reaction with other viral genomes, including spring viremia of carp virus, koi herpesvirus, cyprinid herpesvirus 2, and infection spleen and kidney necrosis virus. This method has been used for the rapid detection of CEV in diseased koi carp. The results were accurate and reliable, providing an effective and useful method for the on-site diagnosis of CEV.

Abstract:Sinking and floating reefs are the main types of artificial reefs, and have been widely used in the development of marine ranching. The floating reef is usually used to trap and protect fishes distributed in the middle and upper water layers. Compared with a sinking reef, the floating reef is less restricted by seabed conditions and demonstrates better performance in the seabed with silt substrate. However, the floating reef can be greatly affected by the dynamic ocean environment, such as waves and current, as its main body is set in the middle and upper water layers. Thus, the structural safety and stability of floating reefs are key points for their design and deployment. This study proposes a newly designed multi-functional cage-net floating reef characterized by its function in both fish protection and culture. Moreover, a numerical model has been established to analyze the effects of wave height and water depth on the structural safety and stability of a floating reef anchored by two modes (single anchor rope and multiple anchor ropes). The results showed that under the same hydrodynamic conditions, in the case of a single anchor rope, the total anchor rope force was almost the sum of the forces for the four anchor ropes; however, the total netting force was less than that in the case of four anchor ropes. Wave height had a great influence on the maximum deflection angle of the floating reef. However, anchoring with four anchor ropes can significantly reduce the maximum deflection angle; the reduction becomes more obvious with increasing wave height, effectively improving the stability of the floating reef. Under conditions of constant wave height, the maximum offset of the floating reef decreased rapidly with increasing deploying water depth. Furthermore, there was minimal difference in the movement of the floating reef between the two anchoring modes when the submergence depth of the main body was twice that of the wave height.

Abstract:Tower-type truss artificial reefs have superior structural stability but are large and of low quality. Presently, few studies have investigated the water dynamics of complex structure reefs in China. Based on studies of the flow field effect around the tower-type truss artificial reef, hoping to provide reference to planning and layout. The reef hemline was 10400 mm long, 5000 mm high, 10400 mm wide, and the cement column was 2850 m minimum length. The diameter was 76.3 mm, the large disc diameter of the reef was 1200 mm, the thickness of the large disc was 59 mm, the small disc diameter of the reef was 680 mm, and the thickness of the small disc was 92 mm. Six real flow velocities (0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 m/s) were designed to study the flow field around the reef. According to the similarity principle, the experiment velocities were 0.031, 0.063, 0.095, 0.126, 0.158, and 0.190 m/s. Using a water flume physical model test and particle image velocimetry (PIV) technology, the flow field effect around the tower-type truss artificial reef was evaluated under six different flow velocities. The anti-rolling and anti-slide coefficients were evaluated under different test conditions. The experimental results indicated that for the monomer reef by mode of 45° and 90° against the flow, the average and maximum upwelling velocity was increased with the flow velocity. The maximum upwelling velocity of the single reef 90° against the flow was 15.6%-21.0% the flow velocity, and 45° against the flow was 16.3%-23.5% of the flow velocity. Increases in flow velocity first increased and then decreased the upwelling scale and height, and when the coming flow speed was 0.095 m/s, the maximum upwelling scale and height were achieved. The slow flow area decreased with increasing flow velocity. Under the same flow velocity, the size of the slow flow area with 45° against the flow was greater than 90° against the flow. The length of the slow flow area to the reef height decreased with increasing flow velocity, and the trend decreased with increasing flow velocity. The length of the slow flow area with 45° against the flow was 13-24-fold longer than the height of the reef. The length of the slow flow area with 90° facing the flow was 11-22-fold longer than the height of the reef. The reef remained stable on the sea floor, where the water depth was 20 m and the current velocity was 1.2 m/s.