Abstract:To provide a new option for the early warning, prevention, and control of the typical disaster-causing organism in the adjacent waters of Daya Bay Nuclear Power Station, an acoustic method, supplemented by a trawl survey and underwater video observation methods, was used to study the dynamics, spatial distribution characteristics, and migration trend of in the survey area from January 11 to 14, 2019. As a result, accounted for more than 99% of the captures collected by trawl samples, along with only a very few jellyfish and fish. Biomass density of estimated by the traditional sweeping area method was significantly higher than that derived from acoustic assessment. They showed a linear regression relationship: depicts the result estimated by the traditional sweeping area method and depicts the result derived from the acoustic assessment). According to in situ acoustic detection, the density of resources fluctuated greatly in different periods (0.56-170.30 m²/n mile²). This showed a general trend of first increasing and then decreasing, with the highest value during 22:30-22:40. In the vertical direction, was mainly distributed in the middle and lower waters at 5.2-7.2 m, and there was a clear downward migration trend from 22:50 to 00:10. In the horizontal direction, the biomass densities of in different transects increased gradually from the inside to the mouth of Daya Bay. Combined with dynamic regulation and the underwater video observations of A. chinensis would migrate into Daya Bay during 19:00-23:00, and then move back to the mouth of Daya Bay after 23:00. To further confirm this inference, in situ acoustic detection experiments should be conducted simultaneously in the adjacent waters of the Daya Bay Nuclear Power Plant and the mouth of Daya Bay, and the biotic and abiotic environmental factors, such as feed organisms, water temperature, salinity, and current among other factors should be considered comprehensively to further explore the driving mechanism of the horizontal migration of In conclusion, compared with traditional investigation methods, the acoustic method has many advantages, such as scientific, efficient, and real-time monitoring. Therefore, it can better meet the practical needs of early warning, prevention, and control of cold source biosafety in the Daya Bay Nuclear Power Plant.

Abstract:The Japanese flounder () is an ideal model for studying the metamorphosis of fish. Thyroid hormone (TH) can regulate the right eye shift and lifestyle of as it transforms from a bilateral pelagic larva into an asymmetrical benthic juvenile. At the same time, microRNAs (miRNAs) play a key role during metamorphosis. To research the regulation mechanism of TH, pol-miR-124, and Otx2 in , based on its binding site through bioinformatics analysis. First, we detected the expression levels of pol-miR-124 and Otx2 in adult tissues in the normal group and TH treatment group larvae using real-time quantitative PCR. Then, the 400 bp alignment region of Otx2 3 UTR containing the "seed sequence" was cloned, and the target relationships between miR-124 and Otx2 were verified at the cellular level by constructing a dual luciferase reporter. The qPCR results showed that both pol-miR-124 and Otx2 were highly expressed in the brain and eye tissues; the highest expression at 28 dph was observed in the larvae. Compared with the NC group, the pol-miR-124 expression level was inhibited at 20 dph and 24 dph in the TH group, and the Otx2 expression level was higher than that in the NC group. However, the expression level of pol-miR-124 increased at 28 dph, 32 dph, and 36 dph, but the Otx2 level was lower than that in the NC group. The expression of pol-miR-124 was negatively correlated with the expression of the predicted target expression. Luciferase results showed that the luciferase activity of the pol-miR-124 group was significantly decreased and was the target gene of pol-miR-124. The results of this study form an important research foundation for further revealing the developmental mechanism of the photoreceptor system during metamorphosis.

Abstract:Toll-like receptor () genes that can recognize various pathogens are important innate immune members; thus, they are a hot spot in fish molecular immunology studies. The great blue-spotted mudskippers () inhabit an amphibious environment that has numerous pathogenic microorganisms. Based on this situation, it can be speculated that the might encounter strong selection pressure. In the present study, the complete sequence of and . nucleotide and amino acid sequences of were analyzed using molecular bioinformatics. The molecular evolution analysis of the 5 genes was conducted based on the phylogenetic tree. The tissue expression patterns of the 5 challenge were explored using real-time quantitative PCR. The results showed that the gene was 3071 bp and included a coding region that was 2646 bp, which encoded 882 amino acids. The gene was 3175 bp, and it had a 3033 bp coding region, which encoded 1011 amino acids, and the gene was 3398 bp and had a 3093 bp coding region, which encoded 1031 amino acids. The TLR5, TLR8, and TLR9 molecule structures were similar to those of other species, showing high conservation. The site model detected two sites (647Q, 691S) under positive selection pressure from fish 9 genes. Although there were no positive sites in the other 3 TLR3, and had some adaptive changes during long-term evolution. Furthermore, the branch-site model detected 3 positive sites (76P, 596A, and 603E) from the branch of The results of the branch-site model showed that owing to the transition from the aquatic environment to the amphibious environment, the underwent adaptive evolution. The results of expression patterns in healthy tissues showed that 5 genes were widely expressed in the tissues examined (intestine, eye, kidney, liver, brain, muscle, spleen, and skin), especially in the liver and spleen. Under genes in the liver and spleen increased at first and then decreased, suggesting that the play an important role in coping with bacterial invasion.

Abstract:Vacuolar-type H⁺-ATPase (V-ATPase) is a kind of hydrogen ion transport enzyme, in which subunit c plays an important role in maintaining the normal acid-base environment in cells. To investigate the function of the V-ATPase subunit c in under high pH stress, the full-length cDNA of V-ATPase subunit c in , was first cloned by rapid amplification of cDNA ends (RACE). Then, the response of under high pH stress was detected. Subsequently, RNA interference (RNAi) technology was used to verify gene function. The full length of cDNA sequences consisted of 2128 base pairs (bp), including a 483 bp open reading frame (ORF), which encodes a 160-amino acid peptide with four transmembrane domains. The predicted protein molecular weight of the protein was 16 kD, and the theoretical isoelectric point (pI) was 7.82. Homology and phylogenetic analysis showed that the deduced amino acid sequence was highly conservative, had the highest amino acid sequence identity (99%) with as well. Results of RT-qPCR showed that , and the expression level in the gills was significantly higher than that in other tissues (FcVHA-c reached a peak at 12 h, which was 1.206 times that of the control group, and reached the lowest value at 48 h, which was 0.166 times that of the control group. Under pH 9.2 stress, the expression level of peaked at 1 h. It was 1.577 times that of the control group and reached its lowest value at 12 h, which was 0.104 times that of the control group. The results showed that high pH had a certain inhibitory effect on by RNAi, under the high pH stress, resulted in mortality that was significantly higher than that in the control group ( may play an important role in ion regulation under the condition of high pH stress, whereas excessive high pH-stress inhibits the ability to regulate .

Abstract:The giant freshwater prawn (GFP) is one of the largest freshwater shrimps in the world, widely distributed in the tropical and subtropical regions of Southeast Asia, the Indian Ocean, and the Pacific Ocean. It has become an important cultured species in China since its introduction because of its wide diet, high growth rate, and high economic value. However, the GFP shows slower growth and poor resistance primarily resulting from an inbreeding depression and farming at high density. One male morphotype named as "old males" or "old blue claw" is present commonly among blue claw males, exhibiting developed second legs and carapace with a dark blue body color, and its economic value is very low. Therefore, improved varieties are urgently needed through selective breeding. The body weight is one of the most important traits for selective breeding, which are closely correlated with morphometric traits. To investigate the correlation and differences in phenotypic traits among cultured groups of , a correlation analysis among 12 phenotypic traits, stepwise multiple regression, and path coefficient analysis on body weight and morphometric traits were performed on 490 individuals of selected from Jiangsu Shufeng Prawn Breeding Co. Ltd. representing three cultured groups:females, males, and old males. Compared with the phenotypic traits in the industry standard published in 2002, the growth performance of the present GFP variety has been greatly improved after years of breeding, and a new industry standard for the new variety should be developed and published. The results of correlation analysis and path analysis showed that 1) except for numbers of dorsal and ventral rostrum teeth, the coefficients between the other nine traits and body weight showed extremely significant positive correlations (<0.01); 2) the key morphometric traits attributed to body weight were different in different groups, but body length, carapace length, and length of second leg were the key traits in the three groups. We estimated the multiple regression equations for each group according to the key traits. For each group, the direct effect of each key morphometric trait on body weight was less than the total indirect effects through the other key traits. The hierarchical cluster analysis and principal component analysis showed that females and males clustered together, and their morphometric traits were similar; the highest variation existed between females and old males. Abdominal characters (including abdominal length, abdominal width, and abdominal depth), total length, body length, and length of second leg contributed the most to the differences among the three groups. Among the three groups, females show advantages in the growth of the abdomen, whereas old males have more developed second legs. The present study can provide data for reference not only for the selective breeding of but also for its basic biology and the development of industry standard.

Abstract:Methyl farnesoate (MF) is a sesquiterpenoid hormone that plays a pivotal role in the regulation of metamorphosis and gonad development in crustaceans. MF is the precursor or non-epoxidized form of JH III, the most common juvenile hormone (JH) in insects. Because of the lack of epoxy, which is the target site of juvenile hormone epoxide hydrolase, MF might mainly be degraded by the juvenile hormone esterase (JHE). Juvenile hormone esterase binding protein (JHEBP) binds to JHE and regulates the metabolism of JHE and also play important roles in MF degradation. In this study, we obtained the full-length JHEBP cDNA sequence from the mud crab, Sp-JHEBP was 1,647 bp, with a predicted 891 bp open reading frame (ORF) encoding 296 amino acids with a predicted molecular weight of 33.79 kD. No conserved protein domain was found using the Pfam database, but the Tim44-like domain was relatively conserved in this crab and insects. In addition, the subcellular location prediction suggested that Sp-JHEBP was located in the mitochondria with a high probability, which is consistent with the experimental results in . Phylogenetic analysis revealed that JHEBP was not correlated with the species tree, suggesting that the function of JHEBP might have evolved differentiation with species evolution. Furthermore, the quantitative real-time polymerase chain reaction revealed that mRNA was ubiquitously expressed in all of the detected tissues, with the highest expression in the ovary, followed by the gills, hemolymph, and hepatopancreas. During the larval development, the expression of was the highest in fertilized eggs, and increased form zoea I to zoea V, then decreased to the first juvenile crab stage. In addition, the was up-regulated by high concentration of MF (>5 祄ol/L), and was also induced by FA in a concentration-dependent manner from 0.1 to 5 祄ol/L. Taken together, we hypothesized that participates in MF metabolism through the degradation pathway of JHE. This study will promote our understanding of the MF degradation pathway.

Abstract:The wild populations of Chinese sturgeon () have decreased dramatically since the 1970s because of environmental degradation, overfishing, and construction of the Gezhouba Dam in the Yangtze River. In 1989, was listed as a first-protected animal in China, also it has been on the IUCN Red List as a Critically Endangered species since 2009. The artificial propagation technology of was realized in 2012, and large-scale hatching of larvae is possible. However, the larval to juvenile stage is the main period of disease occurrence, especially when larvae start feeding and juveniles convert bait; there is often high mortality. This has seriously restricted the protection and utilization of the germplasm resources of . Thus, it is critical to understand the development of the immune system. The goals of this research were to understand the early developmental process and characteristics of the immune organs of by anatomical and histological methods. This provides morphological and histological data for the early development of the lymphoid organs of , and also accumulates basic data for the large-scale cultivation of fry. The healthy larvae and juveniles of F₂ with 1-300 dph were regarded as appropriate species for this test. The occurrence of immune organs (head kidney, thymus, and spleen) was observed and recorded by means of continuous paraffin section and microscopic observation. The results showed that the primordia of immune organs from appeared in the order of the head kidney (3 dph), thymus (7 dph), and spleen (9 dph), and small lymphocytes appeared in the order of the thymus (12 dph), head kidney (15 dph), and spleen (33 dph). At 15 dph, lymphocyte bridges were observed between the head kidney and thymus. At 180 dph, Hassall's corpuscles were observed in the thymus, and Melanocyte or Melano-macrophage centers (MMCs) were found in the head kidney, thymus, and spleen. In conclusion, the immune organs of have the characteristics of early primordial differentiation, a slow developmental rate, and a long developmental cycle. Because the structure of the immune system is not fully developed from larval to juveniles, it is suggested that disease prevention and vaccine development should be strengthened in the early cultivation process.

Abstract:The tiger puffer (), the most valuable teraodontiformes fish, is widely cultured in northern China. Because the testes of male tiger puffers are regarded as a delicacy, males usually have a much higher value than females. Therefore, the production of an all-male population holds considerable potential to improve the economic benefit of tiger puffers. The first step to product an all-male tiger puffer population is to induce sex reversal of males by exogenous estrogens and obtain pseudo-females. However, previous studies have indicated that the ovarian development of pseudo-females is delayed after the exposure, with small number and sizes of oocytes. To explore the regulation mechanisms underlying delayed ovarian development in pseudo-females, in this study, tiger puffers were exposed to 10 µg/L E2 for 2 h once a day from 20 to 90 days posting hatching (dph), and genetic male fish from the treatment group (10 µg/L E2) and genetic female fish from the control group (0 µg/L E2) were collected at 90, 180 and 330 dph, respectively. Then, changes in the histological and morphological features of gonads, hormones (FSH, LH, E2, and 17α, 20βOH-PROG), and genes () on the hypothalamus-pituitary-gonad axis, and genes () involved in lipid accumulation were monitored. The results showed that 10 µg/L E2 was able to induce sex reversal in genetic males and obtain pseudo-females, and those pseudo-females were not reconverted into males or intersex at 330 dph. However, the gonadosomatic index, the oocyte number, and the area of previtellogenic oocyte in pseudo-females was significantly smaller than that of the control. Moreover, compared with control females at 90 dph, lower expression levels of a, 20βOH-PROG, as well as higher expression levels of , were detected in pseudo-females. At 180 dph, only the expression levels of were significantly lower in pseudo-females than in the control. At 330 dph, there was no significant difference between pseudo-females and control females among the hormones and genes. The results indicated that concentrations that are high enough of E2 were able to induce and maintain ovarian development in pseudo-females. However, the high concentrations of E2 might affect lipid accumulation in previtellogenic oocytes by suppressingexpression, resulting in delayed oocyte growth in pseudo-females. Furthermore, the high concentrations of E2 might also suppress meiosis initiation, leading to a decreased number of oocytes in pseudo-females.

Abstract:With the development of statistical and computational technology, landmark-based morphometric analysis has widely been used for species classification and identification in recent years, but it has never been used to identify wild from geographically different basins. Therefore, this research was resized to identify different geographical populations of wild collected from the Tumen River (TR), Liao River (LR), Huang River (HR), Yangtze River (YR), Ou River (OR), and Min River (MR). Landmark-based geometric morphometrics analysis was used to compare the morphological characteristics of their carapaces. The main step was to extract coordinate values of landmark-based points on the carapace, and then perform the relative warp principal component analysis and discriminant analysis to distinguish the 6 wild populations, and finally visualize the morphological variation with thin plate spline analysis and grad distortion. The results showed that:(1) in principal component analysis, wild populations could be divided into 6 relatively independent groups by the first two principal components, though the plots slightly overlapped between different populations; (2) the grad distortion map showed that morphological differences of various populations were mainly manifested in the frontal and lateral spines of the carapace; (3) the discriminative accuracy of various populations in the stepwise discriminant analysis was 80%-96% with a certain risk of misjudgment; (4) cluster analysis showed that YR, HR, OR, and MR individuals clustered independently, whereas TR and LR individuals formed another distinct cluster, whether females or males. In summary, landmark-based morphometrics analysis is an effective means to distinguish wild from different basins, but it still needs to be confirmed by traditional morphometrics analysis and genetic analysis.

Abstract:To explore an efficient and feasible treatment technology of mariculture wastewater, with a win-win strategy of achieving the remediation of mariculture wastewater, and also accumulating microalgae biomass, this study investigated two modes of aquaculture wastewater bioremediation (i.e., free-state mode and immobilized mode) with monoculture and symbiotic systems of the microalgae spp. The cell growth and removal of wastewater nutrients, such as ammonium (NH₄⁺-N), phosphate (PO₄^3--P), total phosphate (T_P), and chemistry oxygen demand (COD_Mn) were tested. Under the free-state mode, microalgae-bacteria symbiosis significantly increased the dry cell weight of -P and COD_Mn Under immobilized conditions, the co-immobilization of spp. enhanced the removal efficiency of NH₄⁺-N, PO₄^3--P, and T_P as compared with that of the monoculture treatment in the same mode, and both nutrient uptake capabilities of microalgae and bacteria were mutually enhanced. Overall, the highest removal efficiency of NH₄⁺-N, PO₄^3--P, T_P, and COD_Mn of 96.57%, 98.62%, 89.89%, and 39.09%, respectively, was achieved under the bioremediation of co-immobilization of ⁺-N and PO₄^3--P in effluent reached the national second-level standards of "Water Quality Standards for Fisheries" and "Drainage Standard for Sea Water Mariculture," whereas the value of COD_Mn met the second-level of "Integrated Wastewater Discharge Standard." These results showed that the monitored effluent indexes met the national seawater quality standards and the concept of combining mariculture wastewater treatment with the microalgae-bacteria symbiosis is feasible under indoor laboratory conditions. It also showed that higher purification efficiency can be achieved by co-immobilized microalgae-bacteria symbiosis. In the future, the selection of immobilized materials, the tolerance of microalgae-bacteria symbiosis to high salinity in seawater, and the separation methods of microorganisms from the effluent should be investigated.

Abstract:(Bli) has been widely used as a probiotic and has positive effects on host health of different fish species. The ability to colonize the gastrointestinal tract is an important criterion for probiotic screening, but little attention has been paid to this character. To investigate the colonization characteristics of Bli-A1, full water exchange and feed sterilization with Co⁶⁰ irradiation were employed to avoid their influence on the gastrointestinal microbiome of . A high temperature selective culture method for Bli was assessed for its sensitivity and specificity, and then it was employed to investigate the dynamic characters of exogenous Bli-A1 in the intestine for 42 days with or without fasting. The spores of were used as an inert control to investigate the adhesion ability of Bli-A1 to mucosa in a feeding trial with Bli/Gs=186.4% in feed, and non-adhesion bacteria were removed by washing the intestinal wall. Then, Bil-A1/Gs on the intestinal content and wall were calculated. At last, the potential of Bli-A1 multiplying in the intestine was assessed with a sterile intestinal content culturing assay . With a full water exchange and feed sterilization, the concentration of Bli was reduced to <1 cfu/mL in water and not detected in feed (1.4×10⁴ cfu/g before irradiation). Selective culture for Bli-A1 was successful at 52℃ with a growth rate at 91.5±13.7% in water, 65.9±26.7% in 20% intestinal content homogenate, and 72.5±19.7% in 20% intestinal wall homogenate. It took 21 days for the inert Gs control to be completely excreted from the intestine after withdrawing exogenous supplement (=3, <1 cfu/intestine). When exogenous Bli-A1 supplement was withdrawn, the concentration of Bli-A1 in the intestinal content was sustained at~3.3×10² cfu/g for at least 42 days with continuous sterile feed supplement, whereas no Bli-A1 was detected at 14 days under fasting conditions. In the Bli-A1/Gs feeding trial, Bli-A1 in intestinal content was detectable to at least 28 days after exogenous Bli-A1 withdrawal. Adhesion-related Bli-A1 on the intestinal wall was undetectable at 7 days. At day 0, Bli-A1/Gs was equal to 197.9% in intestinal content, which was similar with the 186.4% in feed. Bli-A1/Gs was equal to 23.7% on the intestinal wall. Although Bli-A1 failed to adhere to mucosa and its adhesion ability was even weaker than that of the inert control, it grew well in intestinal content and reached a concentration of 2.0×10⁷ cfu/g Ictalurus punctatus long-term, unless the fish are fasted. That is because Bli-A1 possessed the ability to grow in intestinal content but fails to effectively adhere to mucosa.

Abstract:The study was conducted to determine the effects of waterborne Cu exposure on physiological, biochemical, and gene expression related to lipid metabolism in via a 96 h acute toxicity experiment. In the present study, were respectively exposed to 0 (control), 0.1 mg Cu/L, and 0.2 mg Cu/L (96-h LC₅₀). The results showed that Cu accumulation in liver, muscle, and whole fish increased with increasing Cu concentration. The order of Cu accumulation was liver>whole body>muscle at the same Cu dose. With the increase in Cu concentration, malondialdehyde (MDA) content and activities of antioxidant enzymes[glutathione peroxidase (GSH-PX), total superoxide dismutase (SOD), and catalase (CAT)] increased in the liver. Acute Cu exposure induced blood cells deposition in veins and dilatation of sinusoids in the liver, and also induced epithelial hyperplasia, clubbed tips, and aneurysms in gills. In the gut, amylase activity increased significantly, yet the lipase activity decreased after acute Cu stress in . In the liver, activities of amylase, protease, and lipase decreased significantly with the increase in Cu concentration. The expression of genes involved in lipogenesis () under 0.1 mg Cu/L exposure was the highest. However, the expression of genes involved in lipolysis () was the highest in the 0.2 mg Cu/L treatment group. Acute Cu stress had no significant influence on transfer factor was significantly up-regulated relative to that of the control. This study revealed the significant effects of Cu exposure on physiological, biochemical, and gene expression related to lipid metabolism in , which provides beneficial guidance for the rational use of Cu in the production process of , and also provides beneficial references to technical indicators for better monitoring of heavy metal pollution in fish production.

Abstract:The goal of this experiment was to investigate the effects of dietary protein levels on muscular amino acids and protein metabolism of Regan. Six diets were formulated that contained 20%, 25%, 30%, 35%, 40%, and 45% protein levels. Each diet was fed to triplicate groups of 30 fish with an initial body weight of (22.42±0.56) g for 60 d. The results showed that both nitrogen intake (NI) and the amount of absolute nitrogen intake (ANI) of Regan increased with the increase in dietary protein levels. The nitrogen deposition (ND), protein efficiency ratio (PER), and net protein utilization (NPU) increased at first and then decreased. Total essential amino acids (TEAA), total flavored amino acids (TFAA), total non-essential amino acids (TNEAA), and total amino acids (TAA) initially increased and then tended to stabilize with the raising supplemental dietary protein level. There was no significant difference in blood ammonia, urea nitrogen, or albumin (ALB) at the feed protein levels of 20%-25%; however, these factors increased significantly after the feed protein level increased significantly after 30%. Total protein (TP) increased gradually when feed protein was lower than 35%, and there was no significant difference among the experimental groups when feed protein was higher than 35%. Both the liver ALT and AST increased at first and then tended to stabilize. There was a tendency for serum ALT to decrease first and then increase. Serum AST was not significantly different in the experimental group with feed protein content below 35% but increased significantly above 35%. Thus, the appropriate amount of dietary protein level can increase the absorption of protein, increase the protein utilization from feed, increase the rate of body protein metabolism, improve the content of essential amino acids, and improve the taste of muscle. However, it can cause a decrease in the protein utilization in the fish body, inadequate absorption of the protein in the intestine, the increase nitrogen excreta, aggravate the liver load, and damage liver cells when the content of feed protein is too high. Under these experimental conditions, the suitable dietary protein level was 30%-35% based on the feed protein utilization, total protein content in blood, and liver and serum transaminase activity.

Abstract:The fish egg is the early stage in the fish life history, which influences the recruitment of the fish population. There are internal relationships between the distribution of eggs and environmental factors. In recent years, influenced by climate change and global warming, the growth and breeding habits of the small yellow croaker () have changed. The spawning ground of the small yellow croaker has shifted. In addition, the range of the spawning ground of the small yellow croaker has extended to the open sea, and the distribution characteristics of temperature, salinity, and depth of spawning grounds have also greatly changed compared with that of the past. The goals of our study were to reveal the spatial and temporal distributional pattern of eggs of the small yellow croaker in Haizhou Bay and its adjacent waters, as well as determine the relationship between this distributional pattern and environmental variables. A two-stage GAM (two-stage Generalized Additive Model) is a flexible method for modeling zero-flatted data, which are typically found in the data collected from ichthyoplankton surveys. This method is to model the distribution of species in two steps, firstly modeling presence/absence data and secondly modeling density of presence observations. In this study, we conducted an ichthyoplankton survey of the small yellow croaker in Haizhou Bay and its adjacent waters during May in 2015, 2017, and 2018. Based on these data, the two-stage GAM between the distribution of small yellow croaker eggs and environmental factors was constructed. The results showed that the abundance of eggs of the small yellow croaker varied greatly among different years. The eggs were distributed in estuarine waters at depths of 10-20 m between 33.5°N and 34.5°N. Additionally, the temperature and salinity were important factors affecting eggs distribution of the small yellow croaker. The eggs were distributed in areas where the sea surface temperature was 17℃ and the sea surface salinity was between 29.5-30.5. Furthermore, the sea bottom temperature ranged from 16℃ to 18℃ and the sea bottom salinity was 29 in high-destiny distribution areas. In addition, the interannual variation in water temperature also affected the abundance of small yellow croaker eggs. The abundance of fish eggs was significantly higher in the years with higher water temperature. This research revealed changes in the distribution and interannual variation of yellow croaker eggs with respect to changes in environmental variables, and consequently could be valuable for understanding the supplementary mechanism of the small yellow croaker, conservation of spawning grounds (e.g., marine protected areas), and quantitative management of the small yellow croaker. Although the coastal waters of Haizhou Bay and adjacent regions were the focus of our study, the framework and results derived in this study could also be applied to other coastal marine ecosystems.

Abstract:As an important fishery resource in the Yangtze Estuary, has high nutritional value and delicious taste. Because of overfishing, environmental pollution, and habitat degradation in recent years, the resources of have declined sharply. As a type of migratory fish, the growth, development, and reproduction of are affected by the freshwater, estuarine brackish water, and seawater environment. Therefore, exploring the habitat history of is of great importance in the protection and management of this resource. To study the habitat history of in the Yangtze Estuary and its adjacent sea area, otolith microchemical analysis of 10 from Chongming Island in the Yangtze Estuary and its adjacent Lvsi sea area was conducted using X-ray electron probe microanalysis techniques. Quantitative line analysis and surface distribution of Sr content showed that Sr/Ca ratios in the otolith core area of existed in Sr/Ca<3, 3C. mystus could be divided into three types:the freshwater incubation field, estuarine brackish water incubation field, and sea water incubation field. The variation in Sr/Ca ratios in the individual otoliths from the core to the edge was highly significant, including low-ratio freshwater habitat (Sr/Ca<3, minimum 2.04±0.87) and high-ratio seawater habitat (Sr/Ca>7, maximum 7.81±0.91). Thus, the habitat history types of could be divided into four types:freshwater-estuarine brackish water type, estuarine brackish water settlement type, estuarine brackish water-seawater type, and freshwater-estuarine brackish water-seawater type. There were freshwater and estuarine brackish water hatching individuals whose habitat types included freshwater-estuarine brackish water type, estuarine brackish water-seawater type, and freshwater-estuary brackish water-seawater type in the adjacent sea area of the Yangtze Estuary. There were sea water and estuarine brackish water hatching individuals whose habitat types included freshwater-estuarine brackish water type, estuarine brackish water settlement type, and freshwater-estuary brackish water-seawater type in the Chongming Island sea area of the Yangtze Estuary. This reflected the similarities and differences between the individuals in Chongming Island and the Lvsi sea area in the Yangtze Estuary. Through this study, it is proved for the first time that there are three incubation sites and four habitat types in the Yangtze Estuary and its adjacent sea area, which accurately reflect the diversity and complexity of the individual composition and life history of .

Abstract:Bighead carp (), an important cultured freshwater fish in China, is one of the four major Chinese carps. The natural habitation of bighead carp in the Yangtse River has been destroyed because of environmental water pollution and overfishing, among other factors. Stock enhancement of bighead carp has been conducted for years, being regarded as a positive fisheries management tool. Currently, hatchery-reared bighead carp juveniles were released into the natural river system to supplement the wild population in the Yangtse River. However, the effectiveness of these enhancement efforts has not be evaluated to date. The application of microsatellite markers for parentage determination is becoming more acceptable and popular in aquaculture. To analyze the effect of stock enhancement of bighead carp, a parentage test based on SSR markers was applied in this study. Fins of 563 brood stocks of unknown sexes and 687 recaptured individuals were sampled. Ten SSR markers were modified using fluorescent dyes (FAM/HEX). Genotype data of all brood stocks and all offspring were screened using an ABI Prism3 730 sequencer. The results showed that the number of alleles of microsatellite markers ranged from 19 to 55, and the mean observed and expected heterozygosities were 0.748 and 0.882. The range of the polymorphism information content (PIC) was 0.797-0.924. The simulation of parentage assignment for the situation of unknown sexes showed the combined non-exclusion probability of 10 loci was 99.996% using Cervus3.0. The results showed that the 42 recaptured individuals were offspring of brood stocks. The study suggested that the total contribution of the brood stocks to the wild population was 6.11% in the Jiangsu reaches of the Yangtse River. In summary, this study established an evaluation system of "marking brood stocks-releasing offspring-recapturing-parentage assignment" to assess the contribution rate for the large-scale stock enhancement. The evaluation system was used in this study to monitor all offspring of the marked brood stocks, which achieved the goal of one-time labeling and multi-year monitoring. A microsatellite gene bank was constructed using 10 microsatellite loci for brood stocks from 2016 to 2018. Future research should pay more attention to the assessment of genetic differentiation between the released population and wild population. This study will provide technical support for the stock enhancement process of bighead carp.

Abstract:To understand the dynamic patterns of the permanganate index (COD_Mn) and impact factors in the surface water of the mainstream of Xijiang River, seasonal investigations were conducted between Dawan of Hongshui River and Zhaoqing of Xijiang River from September 2017 to June 2018. The water quality was analyzed and evaluated basing on the present study. During the investigation, the COD_Mn concentration varied in the range of 0.73~4.83 mg/L, and the mean value was 2.67 mg/L. The seasonal COD_Mn mean value were 3.08 mg/L (June), 3.03 mg/L (December), 2.94 mg/L (September), and 1.62 mg/L (March). The 13 sample stations were clustered in three groups, and the highest content of COD_Mn was found in cluster Ш, followed by cluster I, with the lowest in cluster II. Results of pollution conditions based on COD_Mn were in the range of 0.18~1.21, whereas the corresponding water quality levels were "no pollution" to "light pollution." The temporal water pollution for the annual average content of COD_Mn in water from the 13 sites in descending order was December, June, September, and March. The water quality identification index and levels based on COD_Mn showed that at most times in one year the water quality classification belonged to class I or II, and the last times belonged to class III. Specifically, water quality in March was best with assigned to class I, followed by periods in September and December, which was belonged to class II, and the worst water quality was in June, which belonged to class II to III. Correlation analysis with other physical and chemical factors showed that COD_Mn had a significant positive correlation with water temperature and total phos phorus, and it was significantly negatively correlated with salinity, dissolved oxygen (DO), secchi depth, total phosphorus, nitrate nitrogen, nitrite nitrogen chlorophyll a, and N:P. Stepwise regression analysis showed that COD_Mn concentration was significantly affected by total phosphorus, phosphate, and DO. According to the present study, it was determined that the water environment in mainstream of Xijiang River was lightly polluted and the water quality was better than most of the other rivers in our country. It was also concluded that the hydrodynamic situation of the river and human settlements near the sampling area were the factors affecting the COD_Mn concentration. Additionally, it was determined that the reducibility of organic matter came from "point source pollution" in the investigation area, which was in common with the sources of water total phosphorus mass.

Abstract:To understand the effects of fishing and factors influencing the Antarctic krill () trawl operations, operation parameters, net depth, acoustic data, and other information were collected by the krill trawler "Long Teng" of the China National Fisheries Corp., Ltd. fishing in the Southern Ocean from December 2017 to June 2018. The mass center depth and expected catches in the net of the Antarctic krill swarm were obtained by an acoustic method, and the fishing efficiency was quantified based on the net position and fishing log. Then, the GAM statistical model was used to analyze the degree of deviation between the net position and mass center of the krill swarm under different towing speeds and warp lengths to study the fishing efficiency of the net. The results showed that:(1) The depth of the krill swarm mass center was (37.29±9.72) m, the depth of the net position during stable towing of the trawl was (30.72±10.41) m, the adjustment range of the net position was (11.52±7.09) m. The deviation between the net position and the mass center depth of the krill swarm was (6.33±3.58) m. (2) The catch per haul was (16.25±6.77) t, the total amount of krill entering the net mouth when the net mouth was always aligned with the krill swarm mass center during the towing process was (27.06±10.19) t, and the fishing efficiency was (63±19)%. (3) The depth difference between the net position and the mass center of the krill swarm had an extremely significant influence on fishing efficiency (<0.001), and when the two were in good agreement, the fishing efficiency was high. The net position went up with the increase in the towing speed and a significant correlation was found between towing speed and fishing efficiency (<0.05). The net position went down with the increase of the warp length, but there is no significant correlation between the change in the warp length and fishing efficiency (=0.087). The results of this study will contribute to the effective use of krill behavior in Antarctic krill trawling operations, the improvement of net performance, and improvement of trawling efficiency.

Abstract:Epizootic ulcerative syndrome (EUS), caused by is an invasive disease of both wild and farmed fish in freshwater and estuarine environments. After it was first described in Japan in 1971, the disease spread widely across Asia and to some regions of Australia, North America, and Africa. In Asia and Africa, the spread of the disease has substantially affected the livelihoods of fish farmers and fishermen. No reports on the presence of the disease have been made in China. In 2012, a similar EUS of broke out in Guangdong Province, China. The ulcerative clinical signs were observed on the dorsal, ventral, and caudal dermal and muscular layer, and were especially prominent on the nape, opercular, and truncal regions. To diagnose the with the suspected EUS, isolation and identification of the mold pathogen were conducted, histologic observations were made of ulcers, and morphology observations were made. The technologies, which were used for the isolation, purification, pathological histology, squashing of tissue, scanning electron microscope technology, and HE and Grocott hexamine silver staining were applied for the identification of the pathogenic morphology, molecular biology, and histopathological observation of the suspected epizootic ulcerative syndrome. The typical filamentous hyphae were isolated from the ulcerated tissue and morphology of the and the original generation of spore were observed under optic microscopy. The hyphae were nonseptate with irregular walls and occasional branches and approximately 10-20 μm in diameter. ITS sequence amplification analysis showed that it was 100% homologous with . The histopathologic changes of the infected fish were observed under optic microscopy. A highly invasive fungus was associated with the EUS in . By squashing the tissue of the ulcerative dermal and muscular layers, large numbers of hypha were observed. A large number of fine filamentous fungi were observed in the muscle tissue by SEM. At necropsy, ulceration and muscle atrophy were noted. The histological sections of skin from multiple ulcerative areas had exuberant hyphae invading through the ulcerated skin. The fungus invaded and proliferated tissues away from the site of dermal ulcers and even penetrated into the skeletal muscle. In more severely affected areas, granulomatous inflammation was also present, and was characterized by numerous macrophages, few lymphocytes, and scant cellular debris. The surrounding muscle fibers were fragmented, vacuolated, and disrupted with loss of cross striations and separation of the fibers. Using Grocott hexamine silver stain, the section of the ulcerative areas more clearly showed the hyphae. The disease was diagnosed as EUS.

Abstract:In recent decades, the incidences of metabolic syndrome of cultured fish caused by unbalanced nutrition components or excessively large energy intake, have dramatically increased globally, and triggered gut inflammation, metabolic disorders, body stress, and decreased immunity defense. Related studies have mainly focused on target tissues of the body, such as the liver and adipose tissue. However, intestinal microbiota in fish, as another most important "tissue", is usually neglected. The gut microbiota plays an important role in the process of growth and development, immune defense, energy absorption, and metabolism of lipids or glucose. To deeply address the relationship among the feed, gut microbes, and lipid metabolism in fish, we firstly clarified the main composition and structure of the gut microbiota in marine and fresh water fish. Then, the effects of feed lipid nutrition on intestinal microbes were analyzed, including the lipid source type and level. Regarding the relationship between the gut microbes and the body lipid metabolism, the causality and effects of the gut microbes on the lipid metabolism were expounded. Specifically, possible mechanisms of host lipid metabolism disorder because of altered gut microbes were described, focusing on the production of short chain fatty acids (SCFAs), lipopolysaccharide (LPS), bile acids, trimethylamine oxide (TMAO), and the permeation of the gut epithelial cells. In particular, several strategies regarding lipid metabolism regulation based on the microbes were advanced, such as the application of new feed sources, prebiotics, and probiotics. Thus, we suggested that the structure and compositional change of the gut microbiota could be used as the symbol for the dysfunction of host lipid metabolism. Furthermore, taking steps based on the theory of the gut steady-state will provide feasible ways to improve the lipid metabolism dysfunction of fish, including clarifying the interactive mechanisms between the microbes and the host, and exploring indigenous probiotics depending on the culture dependent methods and micro-ecological agents.

Abstract:Tibet is rich in water resources. Fish evolution is closely related to the uplift of the Qinghai-Tibet Plateau and the evolution of natural environment isolation. Fish parasite fauna closely related to fish and water environment has also gradually attracted attention. Preliminary studies have shown that although the species of fish in Tibet are single, there are many species of parasitic worms in the digestive tract of fish, showing a high diversity. Some species of Clonorchis and Echinococcus endemic to schizophrenia, as well as some species of threadworms and tapeworms with birds as their final hosts have been found. The composition and evolution of fish parasite fauna in Tibet may be affected by the unique releasing habits and migratory bird migration, the construction of hydropower projects and the status of water pollution, as well as the decline of indigenous fish resources and climate change in the Qinghai-Tibet Plateau. The investigation of parasite fauna can provide detailed data for the species, distribution and quantity of fish parasites in this area, further understand the formation and evolution process of parasites, clarify the relationship between environment and parasite diversity, and provide scientific basis for the development and utilization of fishery resources in Tibet. In this paper, the above problems are summarized and discussed.

Abstract:Chinese sucker is under national first class protection, the resources has declined significantly in recent years. In order to restore the natural population, releasing and enhancement have been carried out. In this study, 10 tagged Chinese sucker (5 females and 5 males, average body weight 12.5 kg ±5.4 kg) were released in the Yibin reaches of the upper Yangtze River in March 2018, the movement characteristics of the releasing fishes were monitored by 20 fixed stations for nearly 500 d. The monitoring results showed that there were 4 individuals with short-term upward movement and the remaining individuals continued to downward movement. The average moving distance of the released fishes was 456.2 km ±335.8 km, the longest movement was to the Zigui reaches. At the end of the monitoring period, 5 individuals were distributed in the Yibin-Jiangjin reaches, 4 individuals were distributed in the Jiangjin-Zhongxian reaches, and 1 individual was distributed in the Badong-Zigui reaches. The average speed of the released fishes was 2.31 km/h ±2.03 km/h, and the maximum downward and upward speed were 35 km/h and 1.04 km/h, respectively. The downward speed was higher than the upward speed. The average moving speed did not differ between different reaches, but there were differences in time periods. The moving speed within 20 d after releasing was higher than 40 d later. The average habitat depth of the Chinese sucker was 6.24 m±4.84 m. Along with the downward movement, the released individuals chose deeper inhabitation. The individual had a large variation of habitat depth in a single day. Based on the monitoring results, increasing the number of released matured Chinese sucker and adding more releasing sites were suggested.