Abstract:Single-cell RNA sequencing (scRNA-seq) is a revolutionary technology for high-throughput sequencing of RNA within individual cells. Since its introduction in 2009, this technique has undergone continuous updates and iterations, proving to be a transformative tool in the field of life sciences. It has found wide-ranging applications in developmental biology, neurobiology, immunology, microbiology, pharmaceutical research, disease treatment, among other fields, demonstrating broad prospects. The versatility of scRNA-seq lies in its ability to unravel the intricate heterogeneity and complexity of RNA transcripts within cells, thereby facilitating the exploration of different cell types and their functions in organisms. As scRNA-seq technology continues to evolve, with advancements towards multidimensionality and spatial resolution, it has emerged as a powerful tool for dissecting complex biological phenomena at the cellular level. In recent years, the widespread adoption of scRNA-seq has been facilitated by reduced sequencing costs and enhanced technology stability. This has led to its rapid expansion beyond model organisms to non-model species like crops, livestock, and aquatic animals. The extension of scRNA-seq to these organisms has yielded transformative insights into cell heterogeneity and function, marking a paradigm shift in our understanding of these species. Notably, within the realm of aquatic animals, scRNA-seq has gained substantial traction, driving a profound exploration of cellular dynamics and mechanisms underlying various physiological processes. This paper provides a comprehensive overview of scRNA-seq technology, its sequencing methodologies, and its applications in aquaculture animals, alongside a synthesis of relevant research findings. It encapsulates the breadth of scRNA-seq applications in aquaculture, encompassing diverse sample preparation techniques and sequencing platforms while highlighting its inherent advantages in studying aquatic animal biology. Furthermore, it delves into the challenges encountered in applying scRNA-seq to aquatic animals. These challenges include the scarcity of marker genes, limited availability and inconsistent quality of reference genomes, and the need for further experimental refinement in single cell suspension or single nucleus preparation methods. Moreover, this paper offers a forward-looking perspective on potential applications of scRNA-seq in aquaculture, envisaging its role in advancing our understanding of cellular function and regulatory mechanisms in aquatic organisms. By illuminating unexplored avenues for research and innovation, it seeks to inspire further investigations leveraging scRNA-seq to unravel the complexities of cellular dynamics in aquaculture animals. Through interdisciplinary collaboration and technological advancements, scRNA-seq stands poised to catalyze transformative discoveries that will shape the future of aquaculture and contribute to sustainable practices in food production and environmental conservation.

Abstract:The mucosa-associated lymphoid tissue is the first line of defense against pathogens in fish. In recent years, the nasal-associated lymphoid tissue (NALT) of fish has attracted worldwide attention from researchers, and has proved to be an important site for antigen recognition and initiation of mucosal immune response in olfactory organs. NALT exerts a rapid local immune response following bacterial, viral and parasitic infections. Intranasal inoculation of fish targeting NALT can provide excellent immune protection. However, the complex network of cells and molecules in NALT and their interaction mechanisms are still largely unknown. Here, the latest progress in studies on the structure and function of olfactory organs, cellular and molecular networks and immune response of NALT, as well as response to intranasal inoculation and its immunoprotective effect on fish are reviewed. This information will promote understanding of the immune defense mechanism exerted by fish NALT locally in the mucosa, which will benefit the design and development of novel mucosal vaccines.

Abstract:Interleukin 10 (IL-10) is a multifunctional cytokine that participates in the immunity of the body. It is secreted by various immune cells such as monocytes and macrophages, and plays an important role in the development of various diseases such as tumor, infection and immune diseases. A variety of scleractinian fish IL-10 has been clonally expressed and has shown immunomodulatory effects, and there are a number of studies on the biological activity, mechanism of action, and regulatory mechanism of IL-10 in fish. To provide a reference for future studies and applications of fish IL-10, a literature review is conducted in terms of its genetic structure, transcriptional expression, origin and evolution, biological activities and functions, as well as fish IL-10 receptor and signaling pathway.

Abstract:In the marine environment, salinity is one of the key factors affecting the survival, growth, maturation, and reproduction of shellfish, and their life activities are constantly influenced by the changes of salinity in the local marine environment. Research on the mechanisms of adaptation to salinity stress in marine shellfish has been an ongoing concern of scholars, and a large number of studies have shown that salinity stress affects biological processes such as growth and survival, osmotic adjustment, energy metabolism, and immune response of marine shellfish. In recent years and following the development and application of genomic and transcriptomic technologies, more and more studies have been conducted to explore the adaptation mechanism of marine shellfish to salinity stress at the molecular level. Therefore, this paper reviews studies on osmotic regulation, energy metabolism regulation, immune response, transcriptome and genome in the adaptation mechanism of marine shellfish to salinity stress, and then proposes the development potential of euryhaline shellfish in the field of saline alkali water. It can provide theoretical reference for the genetic breeding and healthy culture of marine shellfish.

Abstract:Cephalopods are one of the most important fishery resources, whose fishery biological characteristics are extremely vulnerable to changes in the marine environment. The ocean is the main storage carrier of energy in the climate system. The changes of marine environmental factors in recent years were caused by frequent climate change events, and have directly or indirectly influenced the fishery biological characteristics and even fishery of cephalopods. Therefore, this study summarizes the impact of climate change on cephalopods from the three perspectives of reproduction, age and growth, and early life history, and put forward an outlook. The results showed that the fishery biological characteristics of cephalopods were easily affected by the occurrence of climate change events mainly through the marine environmental factors of temperature and primary productivity. At present, the objecrts of relevent researches were mostly economic species such as Ommastrephidae and Loliginidae, and most studys concentrated on the marine environmental factor of marine temperature. In the future, long-term marine environmental data of other factors should be applied into the researches for impact of climate change on other cephalopods species. The purpose of this study is to provide a theoretical basis for analyzing the impact of climate change events on fishery biological characteristics of cephalopods, and to provide scientific guidance for sustainable development of cephalopod fisheries under frequent climate change events in recent years.

Abstract:In recent years, the wild fisheries resources have been decreasing, the aquaculture production has been flourishing, and meanwhile the fish welfare has gained increasing attention from the public and scientists. Under these backgrounds, environmental enrichment, as a new technology in the fields of aquaculture and fisheries, has gained wide attention and is considered to have great potential in improving life skills of released fish, increasing the production output of farmed fish, and improving the welfare of captive fish. Environmental enrichment refers to the methods of environmental optimization aimed at increasing production yield, improving fish welfare, controlling fish behaviors and improving physiological status by a deliberate increase in environmental heterogeneity and complexity of water environment. In general, the international studies on environmental enrichment technology has been flourishing, and the theoretical system is constantly improved. However, relevant research in China is still in the initial stage. This paper first briefly introduces the concept and classification of environmental enrichment, and then reviews the effects of physical enrichment (which has received the most attention at present) on fish aquaculture-related traits (such as aggressive behavior, stress response, metabolism, and growth) and adaptive behaviors and individual fitness after release. This review focuses on the possible causes and the potential neuroplasticity mechanism of the differences in results between studies and discusses the shortcomings of the previous studies and future directions of the field. This review aims to provide reference for research in this field and provide valuable information for sustainable aquaculture and stock enhancement programs.

Abstract:The research on fish nutrition and feed started in 1950s, and the paradigm in this field was established based on that of researches targeting human beings and terrestrial animals. In the past seven decades, based on the paradigm, researches on fish nutrition and feed generated a great amount of valuable data, which promoted the fast development of technology, production and industry of aqua-feed. Challenges of natural resource depletion and environmental pollution to aquaculture industry has been growing with the worldwide expansion of aquaculture scale, and farming practices always raise more and higher demands or standards on aqua-feed. It is widely noted that the formulated feed designed on basis of the research on nutrition and feed for some carnivorous fish species cannot be used in commercial fish farming with success. The fact reveals that results of fish nutrition and feed research conducted following the current paradigm cannot well meet the demand of modern finfish aquaculture. In this paper, the author reviews results of the researches about nutrient requirement and dietary fish meal replacement for Micropterus salmoides and Larimichthys crocea, two carnivorous fish species with commercial importance in inland finfish aquaculture and marine finfish aquaculture in both the world and China. The application of formulated feed in commercial farming of M. salmoides and L. crocea is full of twists and turns, and these fishes had to be fed with raw fish diet for a long period due to the formulated feed did not provide fast growth displayed by the fish fed with raw fish diet. At present, it is known the poor growth of M. salmoides and L. crocea fed with the formulated feed was attributed to the obviously underestimated dietary protein levels. Earlier studies reported that the optimal dietary protein level was 400-440 g/kg for M. salmoides, and 450-470 g/kg for L. crocea. Latter studies reassessed dietary protein requirements of these fishes, and revealed the optimal protein levels for M. salmoides and L. crocea are 480-510 g/kg and 490-520 g/kg, respectively, which are much higher than those reported in the earlier studies. Growth of M. salmoides and L. crocea fed with the formulated feed containing the optimal protein content are comparable to that of the fishes fed with raw fish diet. The story of formulated feed application in M. salmoides and L. crocea farming reveal the necessity of paradigm shift of fish nutrition and feed. The author indicates that the disadvantages in the currently used paradigm include the following: ① The paradigm emphasizes the role of food in regulating fish growth, but ignores the roles of fish genetics and environmental conditions other than food in determining growth and feed intake of fish. ② The paradigm emphasizes that individual growth of fish reflects its nutrient requirements and demand on feed quality, but ignores that individual growth of fish cannot completely represent yield and economic income of commercial fish farming. ③ The paradigm emphasizes the importance of fish growth and feed utilization efficiency as indicators in evaluating benefits of fish farming, but ignores that the negative impacts of fed aquaculture on natural resources and environment are the bottle-neck limiting sustainability of aquaculture industry. ④ The paradigm ignores the effect of basal diet formula in evaluating nutrient requirements and feed quality, and the use of unreasonable basal diet in some research results in erroneous or senseless conclusion. To diminish the aforementioned disadvantages, the author proposes to improve the concept, theory and method of the currently used paradigm. ① Emphasizing the importance of fish genetics and the environmental conditions except food in determining growth and feed intake of fish. Emphasizing that growth potential of fish determine its nutrient requirement, while emphasizing that nutrients from diets can support and modulate fish growth. ② Emphasizing the interaction between different dietary nutrients, and emphasizing that different feed ingredients play their own role in establishing nutrient balance of diet formula. ③ Emphasizing the importance of genetics and population structure of the test fish used in feeding trials. Emphasizing the magnitude of difference in growth between individual fish fed with different diets is an indicator for assessing nutrient requirement and feed quality. Emphasizing the impacts of diet formula on natural resources and environment, which are factors limiting sustainability of aquaculture industry. After the shift or improvement, the paradigm for fish nutrition and feed research will be better in accord with the situation and demand of modern aquaculture farming practices. The results of nutrition and feed research conducted following the shifted paradigm will be more reliable and accurate for diet formula design of aqua-feed, and the formulated feed will be more successful in application in commercial aquaculture farming.

Abstract:Due to the needs of environmental protection and cost control, the amount of plant feedstuffs used in aquatic formula feed is increasing. Plant feedstuffs are rich in dietary fibers (DFs), which resulted in over 30% of DFs contained in common commercial aquatic commercial feeds. However, their impacts on fish physiology are still largely overlooked. This article introduces the definition, classification, physicochemical properties, fermentability, and content of DFs in common plant feedstuffs, with a focus on the research findings of the author and team in the fish physiology of DFs. We noticed that hemorrhage, white feces, enteritis, skin-rotting, gill-rotting, hepatic steatosis and fibrosis, green liver, white liver, gallbladder enlargement and even mass deaths could be induced in yellow catfish (Pelteobagrus fulvidraco) when diet included 20%-30% DFs. Similar symptoms had also been observed in largemouth bass (Micropterus salmoides) and grass carp (Ctenopharyngodon idella) fed high DFs diet. The pathogenic effect of DFs was related not only to the content of DFs in the diet but also to the types of DFs. Pectin was much more pathogenic to P. fulvidraco than cellulose. The pathogenic mechanism of DFs is related to their interference with bile acids (BAs) homeostasis and intestinal microbial homeostasis. DFs have the capacity of binding to BAs, which prevents BAs from activating BA receptors such as FXR. FXR negative feedback regulates the synthesis of BAs and inhibits inflammatory reactions. As a result, high levels of DFs caused hypersynthesis of BAs, increasing of the BAs level in tissues and their hydrophobicity, and interfed with the circadian rhythm of BAs, further inducing inflammatory reactions and tissue necrosis due to the cytotoxicity of BAs. Some DFs are fermentable, which caused structural changes in the gut microbiota (might also be duo to the antibacterial effect of BAs). The disorder of intestinal microbial homeostasis further aggravates metabolic disorders, including BAs metabolic disorder. The disease symptoms and progression induced by DFs can also be improved by the other stress factors. Based on the pathogenesis of DFs, the diseases can be prevented and controlled by limiting the intake of DFs, adding BAs and taurine to the diet, and avoiding the superposition effect of DFs with other stress factors. This study for the first time elucidates the pathogenicity of excessive intake of DFs on fish and its potential mechanisms, providing a new perspective for the high-value utilization of plant feedstuffs and optimization of feed formulation, suggesting a new approach for fish disease prevention and control. Further clarification should be provided on the types, levels, and characteristics of DFs in different plant feedstuffs, as well as the tolerance range of aquatic animals to DFs.

Abstract:The olfactory organs development of blunt snout bream (Megalobrama amblycephala) was investigated using histological and morphological methods. The results revealed that the olfactory organs of M. amblycephala were positioned on the back and in front of the eyes. The olfactory epithelium (OE) was oval-shaped near the base of the olfactory cavity. The olfactory placodes were parallelly arranged in the cranio-caudal direction. There were concave marks on the olfactory fossa’s periphery when fish were hatching out. Afterwards, an elongated olfactory placode was formed in the olfactory fossa’s core. The arrangement of the primary olfactory placodes of the unilateral OE were from loose to tight with M. amblycephala growth. The height and number of the olfactory placodes, as well as the overall surface area of the OE gradually expanded and stabilized in the adult stage. qRT-PCR were used to studied the expression patterns of representative ORs. The results showed that ORs expression differed in different stages and tissues of M. amblycephala. ORs Beta-2, 9, 10 and 11 were highly expressed at several stages of embryonic development, including the blastocyst stage, blastopore closure stage and olfactory lamellae stage (P<0.01). Beta-2, 9, 10, 11 and Epsilon-7 were weakly expressed at 3 to 15 dpf, in the larval and juvenile stages, but highly expressed at 30 to 60 dpf (P<0.01). Beta-2, 10, 11 and Epsilon-10, 13 were strongly expressed in the OE of 4 periods from juvenile to adult stages (including 3, 6, 12 and 24-month-old) (P<0.05). Beta-2, 9, 10, 11 and Epsilon-7, 10, 13 were also highly expressed in the OB (olfactory bulb) in 3-month-old M. amblycephala (P<0.01), but not expressed in the 6 to 24-month-old stage. Beta-2, 11 expression levels were low in the brain at the 4 age periods (P<0.05). These findings provide theoretic evidence for further exploration of the functions of ORs in fish, and deepen the research on fish olfactory recognition.

Abstract:Golden trevally (Gnathanodon speciosus), a marine fish that combines ornamental value with edibility, is a suitable species for marine cage culture. At present, there are few studies on G. speciosus in China, while the studies abroad mainly focus on its adaptability to environmental factors, growth performance, feeding and nutrient requirements, as well as microsatellite sequencing. The studies on its reproductive characteristics and embryonic development is still lacking. Therefore, in this paper, the fertilized eggs of G. speciosus were obtained by artificial oxytocin and observed, in order to elucidate the characteristics of its embryonic and post-embryonic development. The hatchery conditions of the fertilized eggs were as follows : salinity 30.26±0.67, temperature 24.72±0.32 °C, pH value 7.46±0.12, dissolved oxygen 5.13±0.33 mg/L and light intensity 3000 lx. The results showed that the zygotes were transparent floating spherical eggs with an average diameter of 764.29±14.74 μm and a single oil bulb with an average diameter of 166.32±18.28 μm. Embryonic development included 8 stages i.e. fertilized egg stage, blastodisc stage, cleavage stage, blastula stage, gastrula stage, neurula stage, organo-forming stage and hatching stage, subsequently subdivided into 24 stages. The fertilized eggs were hatched out at 18 h 30 min after fertilization followed by the larval stage. According to the absorption of yolk sac, larval stage was further divided into pre-larval stage (0-3 days, not complete absorption of yolk sac) and post-larval stage (4-20 days, complete absorption of yolk sac). The total length of the hatched-out larvae was 1 520±19 μm. The yolk sac has been completely absorbed at 3 days post hatchery (DPH), and the oil globule disappeared at 6 DPH with the appearance of swimming bladder. At 20 DPH, the posterior part of spinal column was curved which was the mark of juvenile stage, meanwhile, the fins and the digestive system were fully developed with a great amount of pigments deposited on the surface of the body, which were the symbols for its ability to live independently. The larval development belonged to an allometric model with faster speed at the early stage and slower speed at the late stage. The development pattern of G. speciosus is in line with typical bony fish, and the development time was shorter than those of other species of Carangidae. The embryonic and post-embryonic development characteristics of G. speciosus were close to those in Trachinotus ovatus, which was the main species of marine ranching in Guangdong province and Hainan province in China. In the process of exploitation and industry development of G. speciosus, we could benefit a lot from T. ovatus. This study will shed a new light on the breeding of G. speciosus in the future.

Abstract:In order to investigate the effects of carbonate alkalinity (CA) on the growth and ovary development of the ridgetail white prawn Exopalaemon carinicauda, three CA gradients of 3 mmol/L (control group), 5 mmol/L and 8 mmol/L were set to culture E. carinicauda for 60 days, and the effects of different CA stress on the growth performance, tissue structure, enzyme activity and ovary development were compared. The results showed that there was no significant difference in growth gain, weight gain or survival rate between 5 mmol/L and control groups (P>0.05), while those of 8 mmol/L group was significantly lower than control group (P<0.05). Hepatopancreas sections showed that the morphological structure of the lumen was severely deformed in 8 mmol/L group. Gill sections showed that gill filaments were swollen, blood cells swelled, epithelial cells were seriously damaged, and the stratum corneum space was deformed in 8 mmol/L group. Carbonic anhydrase activity in 5 mmol/L group was significantly higher than control group (P<0.05), while Na⁺/K⁺-ATPase activity in muscle showed no significant difference (P>0.05); there was no significant difference in carbonic anhydrase in hepatopancreas (P>0.05), and Na⁺/K⁺-ATPase activity in hepatopancreas of 8 mmol/l group was significantly lower than other groups (P<0.05). Na⁺/K⁺-ATPase activity in gill of two stress groups was significantly higher than control group (P<0.05). Ovaries of all three groups were able to develop, while only 3 mmol/l and 5 mmol/L groups had E. carinicauda ovary developed to stage Ⅲ; ovary sections showed that the arrangement of oocytes in 8 mmol/L group was loose, and the arrangement of surrounding follicular cells was loose and the number was small. To sum up, E. carinicauda can grow and develop in CA less than 8 mmol/L, but high CA may cause damage to the gills and hepatopancreas, thus affecting growth. At the same time, it is speculated that high CA may also affect the development rate of ovaries. This study provides basic data and reference information for the enhancement and cultivation of white shrimps in saline-alkaline water.

Abstract:Food is the main source of energy for animals, and food abundance affects animal bioenergetics in terms of how energy is allocated among growth, maturation, and reproduction. However, food resources are sometimes insufficient for mussel because of weather conditions, specific periods of their reproductive cycles and food restriction. Marine mussels are one of the most important marine genera globally and are widely distributed in estuarine and marine environments, as well as in the subtidal and intertidal zones, and are commercially important. In order to explore the physiological and biochemical responses and molecular adaptation mechanism of mussels under starvation stress, the survival rate statistics, energy metabolism related enzyme activity determination and gonad transcriptome sequencing and analysis were carried out on two-year Mytilus coruscus under normal feeding (control group) and starvation treatment (starvation group). The results showed that the survival rate of M. coruscus reached 86% after 90 days of starvation. Under starvation stress, the activities of phosphoenolpyruvate carboxykinase (PEPCK) were significantly increased, but the activities of hexokinase (HK), phosphofructokinase (PFK), succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) were significantly decreased (P<0.05). By Illumina Hiseq X10 high-throughput sequencing platform, 31 596 762 and 26 810 506 effective data with unique annotation on the genome of the control group and the starvation group were obtained, and 4 130 differentially expressed genes were screened. There were 2 082 up-regulated and 2 048 down-regulated genes. GO functional analysis showed that differential genes were mainly enriched in metabolic process, organelle tissue and enzyme activity. KEGG enrichment analysis showed that differential genes were significantly enriched in metabolic pathways related to cell division, such as DNA replication, mismatch repair and base excision repair. The results of this experiment showed that mussels could maintain their survival under starvation stress by reducing energy metabolism and slowing down cell division. This study preliminarily reveals the physiological and biochemical responses and molecular regulation mechanism of M. coruscus under starvation stress, which provides important theoretical basis for further analysis of the molecular strategies of mussels in response to starvation stress, and also provides new ideas for revealing their energy utilization and redistribution and physiological countermeasures to adapt to starvation stress.

Abstract:Summer mass mortality is one of the major bottlenecks limiting the green and high-quality development of the Pacific oyster Crassostrea gigas aquaculture in China. The frequent environmental stresses in summer, including high-temperature, rainfall, pathogen stimulation, picophytoplankton abundance and reproductive behavior, are important causes of mass mortality. Monitoring the changes of key environmental factors and health-related indicators in the aquaculture of C. gigas will help to forecast the risk of mass mortality. In this study, two surveys were conducted for C. gigas aquaculture in the North Yellow Sea during the summer heat and rainfall period to monitor the variations of water parameters, picophytoplankton abundance, bacterial abundance, glycogen content and immune-related indicators. It was found that, for the first and second survey in July, the surface water temperature was 25.3 and 24.9 °C, respectively. The salinity for the two surveys was 26.41 and 27.87, respectively. The abundance of diatoms for the two surveys was 3.6×10³ and 3×10³ cells/L, respectively, which was lower than the average level of previous reports, and the diversity of dinoflagellates increased. For the two surveys, the abundance of total bacteria in the water was 2.10×10⁹ and 2.77×10¹⁰ copies/L, respectively, and the abundance of Vibrio was 3.37×10⁸ and 5.40×10⁸ copies/L, respectively. The glycogen content of hepatopancreas decreased to 40.96 and 31.58 mg/g respectively for the two surveys, and the glycogen content of adductor muscle decreased to 6.63 and 8.91 mg/g, respectively. MDA content in gill was 13.74 and 8.69 nmol/mg prot for the two surveys, respectively, and T-AOC in gill was 0.46 and 0.77 U/mg prot, respectively. The expression levels of CgIL17-5 and CgTNF-1 mRNA in haemocytes dramatically increased in the first survey compared to the oysters cultured indoor. The expression levels of CgCaspase3 mRNA in haemocytes increased compared to the oysters cultured indoor, but the differences were not significant. In conclusion, the results showed higher water temperature and lower salinity happened in shellfish farming areas in the summer of 2021. The abundance of diatoms decreased compared to the average level of previous reports, and the diversity of dinoflagellates, a potentially harmful algae, increased. The abundance of environmental bacteria changed during the environmental stresses, and the risk of outbreak of potential pathogenic bacteria Vibrio increased. Organism responses were observed in oysters including lower glycogen content and mild oxidative stress. These results help us to further understand the environmental patterns and response characteristics of the organism during summer and provided a theoretical basis and reference for the prevention and control of the mass oyster mortality in summer.

Abstract:The offshore waters of the North Yellow Sea is a traditional fishery area in northern China, with sufficient bait organisms and high marine primary productivity, which meet the habitat conditions required for the growth and development of various marine fishery resources and are important spawning grounds and habitats for fishery taxa. In order to understand the current community structure of fishery organisms and reveal the main environmental drivers of its spatial and temporal changes, six monthly voyages of the resource bottom trawl and its habitat surveys were conducted from April to November 2021. Abundance-biomass comparison curves(ABC), spatial interpolation analysis, diversity Analysis, CLUSTER analysis and non-metric multidimensional scale ranking(NMDS) were used to analyze the species composition, dominance, relative abundance, diversity, stability and intra-annual succession of fishery organisms community structure; the relationship between spatial and temporal variation of fishery organisms ommunity structure and environmental factors was analyzed by Canonical Correlation Analysis(CCA). The results showed that 89 species were collected, including 50 species of fish, 19 species of crustaceans, 6 species of shellfish, 6 species of cephalopods, 6 species of echinoderms and 2 species of coelenterates. The dominant species from April to November were Engraulis japonicus and Crangon affinis, while the important species were Actiniaria, Liparis tanakae, Loligo japonica, Todarodes pacificus, Metapenaeopsis dalei and Hexagrammos otakii. Compared with past surveys, the pelagic species Konosirus punctatus and Sardinella zunas had a significantly lower catch proportion in this survey. During the survey, many kinds of fishery biological parents and larvae appeared, showing that the sea area has the property of good spawning and nursery grounds. In addition, under the long term influence of protection measures such as fishing moratorium, juveniles of important economic species Pagrus major were found in this survey, and juveniles of Decapterus maruadsi also showed obvious clustering phenomenon, which to a certain extent reflects the development trend of the resource for the better. The community was unstable for most of the survey period. In April, the selective species number in the fishery community began to increase, the community structure was in a state of moderate interference. From May to June, there was a large-scale outbreak of anemone in southern waters of the Zhangzi Island and Haiyang Island, and the marine environment was under great pressure. Therefore, the community was in a state of serious disturbance. In July, the community showed a state of severe disturbance. Since spring and summer are the peak periods of spawning migration, the spawning migration of a large number of fishery organisms formed a relatively continuous migration disturbance. Due to this and the drastic changes in the sea area habitat, the disturbance to the community in July was further intensified. The community in August was in a severely disturbed state, and the diversity level showed a decreasing trend compared with the previous month. The reason for this is that a large number of jellyfish communities appeared in the sea in August, which greatly occupied the ecological niche in the upper ocean space, leading to a significant increase in natural disturbance and a certain degree of damage to the marine habitat. But as was in timing of the peak spawning migration, when migratory fish species gathered, the nutrient channels became more complex, and the community was more resistant to disturbance, so its stability was improved. After four months of fishing moratorium, the community richness and diversity were significantly improved from September to November, but with the end of the moratorium, the ABC curve showed that the community structure was severely disturbed from September to November due to the sudden increase of anthropogenic fishing disturbance. The CCA results showed that among the selected environmental factors, sea surface temperature (SST), sea bottom temperature (SBT), sea bottom salinity (SBS) and chlorophyll-a (Chl.a) were the main environmental factors causing spatio-temporal changes in community structure, among which SST and SBT had more significant effects. During the transition from spring to summer, the offshore waters of the North Yellow Sea gradually entered the warming period, and the warm-temperature species began to migrate into the sea area. The typical species of fishery biological community in the sea area around the southern Yalu River estuary and the central sea area of the Haiyang island gradually transited from cold-temperature species to warm-temperature species such as E. japonicus and T. pacificus. Possibly affected by the edge of the cold water mass in the North Yellow Sea, the communities in the deep water area south of Zhangzi Island and Haiyang Island gradually evolved into cold-temperature species, such as H. otakii and L. tanakae. In autumn, the sea area was still characterized by warm water, and the fishery biological communities in different geographical locations and different water layers of the sea area were basically replaced by warm temperature and warm water species. In addition, according to the Jaccard similarity index and species turnover rate, the species turnover rate of fishery biological community was relatively large during the transition from spring to summer, while the species turnover rate was significantly decreased during the transition from summer to autumn. Traditional resources such as Larimichthys polyactis, Scomberomorus niphonius and Scomber japonicus were still in the process of decline, and the phenomenon of low quality of marine fishery resources was still more significant. The relationships between species composition, quantitative distribution, community structure changes and stability, biodiversity changes and spatial and temporal changes in community structure and environmental factors in the marine area were also elucidated preliminarily. It was found that reproduction, feeding migration, overwintering migratory behavior, human activities and environmental changes of each fishery taxon all have important effects on the turnover of community species, and the resource dynamics of the early replenishment group is particularly critical, while external environmental factors and internal mechanisms of its changes are complex. It is necessary to carry out further study on the early life stage of marine fish and the recruitment mechanisms should be discussed in terms of environmental conditions. This study systematically clarifies the structural characteristics and seasonal succession of fishery biological community in offshore waters of the North Yellow Sea, providing reference and data support for further understanding the current situation of fishery biological community structure and its response to environmental factors.

Abstract:To understand the population characteristics and resource changes of Coreius heterodon in the Yichang section in the middle reaches of the Yangtze River after impoundment of the Three Gorges Reservoir, population parameters and resource status of C. heterodon were analyzed using FISAT Ⅱ software based on the biological data obtained from gillnets deployed in the Yichang section during 2003?2005, 2009?2011 and 2017?2021. Results showed that body length ranges were 118-416 mm, 111-409 mm and 107-380 mm, and weight ranges were 10-1000g, 19-889 g and 16-816 g, respectively. Average body lengths and weights of C. heterodon in the three periods were (230.7±49.8) mm, (217.5±54.3) mm, (267.2±34.1) mm, (195.8±123.6) g, (153.2±118.6) g and (250.3±84.2) g, respectively. Growth indices (b) were 3.015, 3.032 and 2.978, respectively, which belonged to the uniform growth type. The asymptotic length (L_∞) of C. heterodon was 535 mm in 2003-2005, 530 mm in 2009-2011 and 500 mm in 2017-2019, respectively, with growth coefficients (k) at 0.18, 0.14 and 0.15. According to the length-structured virtual population, annual population of C. heterodon were estimated to be 1.10×10⁶, 1.89×10⁶ and 2.10×10⁶, respectively. After the impoundment of the Three Gorges Reservoir, although the C. heterodon in the Yichang section grew at a uniform rate, and the resource increased significantly, the growth rate slowed down and showed a trend of miniaturization. Results in this paper would provide scientific basis for the protection and utilization of fishery resources in the middle reaches of the Yangtze River after the moratorium.

Abstract:As the largest grouper species, the giant grouper (Epinephelus lanceolatus) exhibits rapid growth and significant competitive advantages, hence playing a crucial role in the development of the grouper industry. To understand the impact of artificial breeding and selection on the genetic diversity of E. lanceolatus, microsatellite molecular marker technology was employed in this study to investigate the genetic variation in five representative breeding populations collected from Guangdong, Hainan, and Fujian provinces in China. Genetic diversity analysis within the populations revealed an average number of alleles (N_a) of 7.326 (range: 6.375-8.380), an average observed heterozygosity (H_o) of 0.711 (range: 0.625-0.775), an average expected heterozygosity (H_e) of 0.705 (range: 0.684-0.734), and an average polymorphic information content (PIC) of 0.659 (range: 0.633-0.693). Notably, the breeding population from Xiang'an District, Xiamen, Fujian exhibited the highest genetic diversity. Analysis of molecular variance (AMOVA) revealed that 5.36% of the genetic variation was from between populations, while 95.45% was from between individuals. The genetic differentiation index (F_st) and genetic distance results indicated that the GC (Gancheng) and CP (Changpo) populations clustered together, joined by the AT (Aotou) population and then the XA (Xiang'an) population, with the HL (Huli) population forming a separate branch. The phylogenetic tree analysis showed overlapping of breeding populations without distinct geographical patterns. In conclusion, the breeding populations of E. lanceolatus in these three provinces exhibited high genetic diversity without evident signs of domestication. Overall, this study demonstrates that the breeding populations of giant grouper still maintain a high level of genetic diversity, with a low likelihood of decline due to inbreeding effects. However, the frequent occurrence of diseases and low survival rates in the breeding process may be attributed to imperfect artificial breeding techniques and inadequate aquaculture management. This research provides a theoretical basis for the genetic evaluation and artificial selection of E. lanceolatus. This study highlights the importance of maintaining genetic diversity within cultivated stocks to ensure the sustainability and productivity of aquaculture operations. Despite high genetic diversity observed, the management and traceability of breeding stocks need enhancement to safeguard against potential genetic bottlenecks. The findings underscore the need for ongoing genetic monitoring and responsible breeding practices in the preservasion of genetic health and viability of E. lanceolatus populations.

Abstract:To investigate the differences in muscle quality between common carp (Cyprinus carpio) with different body colors, the present study focused on the blue-gray (BG) and whole red (WR) individuals of the FFRC no. 2 strain C. carpio. The objective was to evaluate the disparities in muscle quality between these two color variants of the C. carpio. Muscle quality variations were assessed by examining parameters such as muscle color, amino acid composition, fatty acid content, and texture characteristics. The results showed that the b* value of BG was significantly higher than that of WR (P<0.05). There was no significant difference in fillet yield, moisture, crude lipid, crude protein, and ash content of the muscle between the two color groups (P>0.05); seventeen amino acids were detected in the muscles of different body color C. carpio, including 7 essential amino acids and 10 non-essential amino acids. Comparisons of glycine (Gly), proline (Pro), histidine (His), and cysteine (Cys) showed no significant difference between the two groups (P>0.05), while those of other amino acids showed significant (P<0.05) or extremely significant (P<0.01) differences between the two groups. There was no significant difference in ΣEAA/ΣTAA between the two groups (P>0.05); the content of myristic acid (C14:0) in BG was significantly higher than that in WR (P<0.05). BG exhibited higher levels of saturated fatty acids compared to WR, while WR had higher levels of monounsaturated fatty acids than BG. Both BG and WR showed similar levels of polyunsaturated fatty acids. The springiness and chewiness of the muscle in WR were significantly higher than those in BG (P<0.05). The research results show that body color has an impact on the muscle quality of C. carpio. This study provides basic data and reference for the improvement of meat quality traits in fish.

Abstract:The construction of dams will hinder the migration of migratory fish, and the water diversion structure and pumping activities will cause damage and death of juvenile or adult fish. In order to solve this problem, measures such as deploying physical barriers can be taken to prevent fish from entering dangerous areas. However, such physical barriers are expensive and difficult to install and maintain. Therefore, as a non-structural measure that does not cause harm to fish, acoustic deterrents are widely used in water conservancy projects. The acoustic deterrent is an important means to prevent fish from entering dangerous areas and protect fish resources. In order to screen sounds as potential acoustic deterrents, this research used six single-frequency sounds (500-3 000 Hz) and a broadband sound (Alligator sinensis roar) as experimental sounds to screen deterrents against Ctenopharyngodon idella juveniles. The behavioral responses of C. idella juveniles to different sounds were compared by alternately broadcasting at both ends of the flume. The results showed that most of the experimental fish responded to the sound, and the roar of the A. sinensis had significantly different effects from other sound groups. In the single-frequency sound experimental group, the average number of responses was the largest when playing 500 Hz single-frequency sound, which was (1.7±0.6) times, while the average number of responses was as high as (5.0±0.9) times when playing the roar of A. sinensis, which was significantly higher than other experimental sounds. In the total average speed, the total average speed of C. idella in the broadband sound group was significantly higher than that in other groups, indicating that C. idella was sensitive to the roar of A. sinensis and escaped. Studies have shown that C. idella shows negative phonotaxis to the roar of the A. sinensis, and the roar of the A. sinensis is a sound that has a driving and deterrent effect on C. idella. This research can provide a reference for the auxiliary means of inducing fish in fish passing facilities and avoiding fish entrainment in water conservancy structures.

Abstract:Filamentous algae, represented by Spirogyra and Cladophora, exist widely in various natural and aquatic waters, and their overgrowth poses a threat to aquatic environment and cultured animals. In order to explore the key factors for filamentous algae occurrence, five pairs of ponds with and without filamentous algae in the same environment and belonging to the same farmers were selected for this study. Their water quality, bioavailable nitrogen and phosphorus in sediment, as well as filamentous algae propagules were detected and analyzed. The results showed that there were no significant differences in total nitrogen and phosphorus levels between ponds with and without filamentous algae (P>0.05), whereas the content of Chlorophyll a in four ponds in with filamentous algae was significantly higher than that in corresponding ponds without filamentous (P<0.05). The average bioavailable nitrogen content in the sediment of ponds with filamentous algae was (15.72±3.60) mg/kg, whereas the average bioavailable nitrogen content in those without filamentous algae was (13.22±1.97) mg/kg, 2.50 mg/kg lower than that of the former. The average available phosphorus content in the sediment of ponds with filamentous algae was (72.26±10.57) mg/kg, and that of ponds without filamentous algae was (50.33±12.62) mg/kg, 21.93 mg/kg lower than that of the former. The ratio of available N/P in sediment was below 0.5 in the five pairs, and the ratio of available N/P in ponds without filamentous algae was 26.32% higher than that in ponds with filamentous algae. Phytoplankton growth could be inhibited in low N/P ratio condition, whereas filamentous algae has strong adaptability to low nitrogen content and N/P ratio environment. Therefore, at the beginning of culturing, the conditions of low nitrogen content and low N/P ratio in the sediment put the phytoplankton at a disadvantage in the initial niche competition with filamentous algae, and even if the OTUs number of phytoplankton detected was larger than that of filamentous algae propagules, it did not make it the dominant species under the above conditions. In addition, the detection of filamentous algae propagules showed that they were widely present in water bodies and sediment of ponds with and without filamentous algae , as well as in water sources, and filamentous algae propagules were detected even in sterilized and sun-exposed ponds. However, the number of filamentous algae propagants could be reduced by sterilizing and sun-exposing ponds. Therefore, quicklime or bleaching powder alone cannot completely eliminate the occurrence of filamentous algae, but can be used as an auxiliary control measure, whereas controling the interspecific niche competition with the regulation of bioavailable nitrogen content and the ratio of nitrogen and phosphorus is a promising direction of controlling filamentous algae worth further study. The results of this experimental study have important reference value for the research and production practice of filamentous algae prevention and control in aquaculture ponds.

Abstract:The aquatic ecosystem is an important part of the earth's environment, and a healthy aquatic ecological environment is an important prerequisite for aquatic ecosystems to provide services and perform their functions, as well as a solid guarantee for the healthy development of modern aquaculture. However, in recent decades, biological invasions of exotic aquatic animals are considered to be a major driving factor in the vanishing of biodiversity in many aquatic ecosystems in China. Some exotic aquatic species have even caused irreversible damage to some of China's aquatic ecosystems, with far-reaching hazards and adverse effects. In the past two decades, with the development in ecology, environmental science and other related disciplines, Chinese researchers have conducted increasingly in-depth research on invasive alien species (IAS). Through extensive analysis of the biological characteristics of invasive alien species and their invasion process and mode, it is found that apart from a few exceptions, biological invasion around the world are almost all caused by the active and passive diffusion of alien species caused by human activities. Among the many factors of alien species diffusion, the introduction and artificial breeding of alien species with economic and trade as the core purpose is one of the important factors, which includes not only the biological invasion caused by alien species themselves, but also the impact of pathogenic organisms carried by alien species on local species, ecological environment, the enormous threat posed to human health and other factors. Internationally, many countries regard the risk assessment of invasive alien species as an important measure for solving the problem of biological invasion. Conducting risk assessments of invasive alien species and formulating more scientific introduction policies and programs on the basis of the assessment results can effectively reduce the obstacles to aquaculture development and economic losses caused by biological invasions and other issues. However, the risk assessment methods currently adopted by most countries in the world are qualitative or semi-quantitative, and with regard to the accuracy of results, there is a significant gap between qualitative and quantitative assessments. Moreover, due to the large differences between terrestrial ecosystems and aquatic ecosystems, there are differences between terrestrial animals and aquatic animal in the process and mechanism of biological invasions. Most risk assessment systems are developed for terrestrial animals, and the adaptability between these risk assessment systems for terrestrial animals and aquatic animal is low, while the existing research and development of aquatic animal assessment systems are still relatively rudimentary. To further refine the research in related fields, this study took exotic aquatic animals as the main research object, analyzed the possible ecological risks and invasion mechanisms of common exotic aquatic animals, and used analytical hierarchy process (AHP) to construct a risk assessment system for the introduction of exotic aquatic animals. This risk assessment system consists of six primary indices (exotic species characterization, ecological risk assessment, pathogen entrance, pathogen exposure, hazard and impact, and exotic species risk prevention and control) and thirty-two secondary indices. Then, it was used to conduct quantitative risk assessments on three typical exotic aquatic animals in China. The assessment results show that the risk value (R) of Atractosteus spatula was 3.948 6 and the risk grade was high, strict introduction strategies and risk prevention measures needed to be formulated, and standardized introduction should be carried out in close communication with relevant departments such as customs. The R of Mizuhopecten yessoensis was 2.908 1, which means the risk grade was medium and it needed to be introduced with restrictions under strict management by customs and relevant departments. The R of Panulirus ornatus was 1.868 8 and its risk grade was low, indicating that it could be introduced if allowed by national policies. The assessment results were highly consistent with the information provided by relevant units such as the Ministry of Agriculture and Rural Affairs, the Ministry of Ecology and Environment, and the General Administration of Customs in China, proving that this risk assessment system has important application value in the risk assessment of the exotic aquatic animals’ introduction. Concurrently, quantitative risk assessment of exotic aquatic animals through the risk assessment system can provide theoretical support for scientific introduction and healthy farming effectively and accurately, and provide decision-making basis for risk management of exotic species.

Abstract:Diets containing high levels of carbohydrate could inhibit the feeding in many fish species, but the relevant mechanisms behind this regulation are not clear. The mandarin fish (Siniperca chuatsi), a typical carnivorous fish, exhibits an apparent anorexia due to its extensive intolerance to dietary carbohydrates, which limits its value as a cultured species. To investigate the existence of a glucose sensing system in the hypothalamus of S. chuatsi and its effect on feed intake, intracerebroventricular (ICV) injections of saline (control), 2-DG (glucose metabolism antagonist, 100 mg/kg) and glucose (10 mg/kg) were performed, exploring the impacts on feeding and glucose metabolism at 3, 6 and 12 h. The results showed that ICV of glucose significantly inhibited the feed intake of mandarin fish, while the plasma glucose levels remained constant at different time points. The expression of glucokinase (gk) were significantly induced at 6 h after ICV administration of glucose, indicating the presence of a glucose-sensing system in the hypothalamus of mandarin fish. ICV administration of glucose significantly promoted the mRNA levels of the cocaine and amphetamine-regulated transcriptional peptide (cart) at 3 h , which may be related to the significant upregulation of mTOR in the hypothalamus (12 h) and liver (6 h) of mandarin fish. In addition, ICV administration of glucose significantly induced the expression of gk (6 h) and pk (3 h) in the liver of mandarin fish to promote glycolysis, suggesting the promotion of catabolism for energy supply through perceived glucose levels in the hypothalamus. In conclusion, this study demonstrates for the first time that gk in the hypothalamus can response to the glucose level, suggesting the potential existence of glucose sensing system in the hypothalamus of mandarin fish, and that ICV administration of glucose regulates the AMPK/mTOR pathway through gk-induced glucose sensing, which in turn regulates the expression of appetite-related genes to inhibit feed intake. The present study would provide a theoretical basis for research on the carbohydrate utilization and feeding regulation in mandarin fish.

Abstract:Lipid oxidation is prevalent in fish feed, which reduces the nutritional value of fish feed and damages the health of aquatic animals. Taurine has been extensively studied as a feed additive to promote fish growth and antioxidant capacity, but its effects on intestinal health need further research. To investigate the effects of taurine on the growth performance and intestinal health of the Yellow River carp (Cyprinus carpio) fed with a lipid-oxidized diet, a total of 225 C. carpio with similar weight at about 8.74 g were randomly divided into five groups: FO, OFO, T0.4, T0.8, and T1.2, respectively. A 10-week feeding trial was performed. The results showed that taurine supplementation alleviated the growth inhibition caused by the OFO diet on C. carpio, mainly by improving final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), and feed efficiency (FE). The oxidized lipid diet inhibited nrf2 mRNA expression in the hepatopancreas and intestine and promoted the mRNA levels of keap1 in the intestine. Appropriate taurine addition can inhibit the decrease of nrf2 mRNA levels and increase of keap1 mRNA levels induced by the OFO diet. Taurine also increased mRNA levels of antioxidation-related genes (gr, gpx and sod). For example, supplementation of 0.8 g/kg taurine significantly increased intestinal gr, gpx, and sod expression levels. In addition, taurine mitigated the decreased intestinal digestive enzyme activity (lipase, amylase, and trypsin), villus height, villus width, and muscular thickness of the oxidized lipid diet. Moreover, taurine restored the decreased alpha-diversity index (Chao1, observed species, Shannon, and Simpson index) of intestinal flora induced by the oxidized lipid diet. Furthermore, supplementation of 0.8% taurine reversed intestinal flora disturbance caused by the oxidized lipid diet, mainly by reducing the abundance of pathogenic bacteria (Aeromonasd and Acinetobacter, etc.) and increasing the abundance of beneficial bacteria (Lactobacillus, Cetobacterium, and Prevotella, etc.). In conclusion, taurine mitigated the negative effects of lipid oxidized diet on the growth performance and intestinal health of C. carpio, and the recommended supplemental level of taurine in the oxidized lipid diet was 0.4%–0.8%. This study lays a theoretical foundation for further exploring the biological function of taurine in fish intestines.

Abstract:In order to avoid competition between aquatic animals and humans, seeking new feed raw materials has become an important direction for the healthy development of aquaculture. Silphium perfoliatum, also known as rosin, has the advantage of “not competing with grain for land”. This study is conducted to investigate the effects of dietary S. perfoliatum (SP) supplementation on the growth performance, antioxidant capacity and lipid metabolism of juvenile Megalobrama amblycephala. Four experimental diets were formulated containing 0% (control group), 2%, 4% and 6% S. perfoliatum (SP). Two hundred and forty healthy M. amblycephala juveniles (3.85±0.50 g) were randomly fed one of the four experimental diets in triplicates (20 fish per tank) for 8 weeks. After the 8-week feeding trial, the growth performance, muscle composition, plasma biochemical indicators, hepatic and intestinal antioxidant capability, and gene expressions related to lipid metabolism were measured. The results showed the following. Compared to the control group, the weight gain rate (WGR) and specific growth rate (SGR) were significantly lower in the 4% and 6% SP supplementary groups (P<0.05). In the 6% group, the final body weight (FBW) was significantly lower than that of the control group (P<0.05), while the feed coefficient ratio (FCR) was significantly higher (P<0.05). As to the antioxidant capability, the levels of catalase (CAT) and superoxide dismutase (SOD) in the intestine were significantly higher in SP supplementary groups compared to the control group (P<0.05). In terms of fat deposition and lipid metabolism, fat contents in the muscle of the 4% and 6% SP supplementary groups were significantly higher than that in the control group (P<0.05). The intestinal lipase activity was significantly lower in the 4% and 6% SP supplementary groups compared to the control group (P<0.05). The contents of plasma triglycerides (TG), cholesterol (TC), high-density lipoprotein (HDL), and low-density lipoprotein (LDL) in the 6% SP supplementation group were significantly higher than those in the control group (P<0.05). Meanwhile, the gene expressions of hepatic fas and srebp1c, relating to lipid synthesis, were significantly activated in the 4% and 6% SP supplementary groups (P<0.05). The gene expressions of hepatic lpl, cpt1a and pparβ, relating to lipolysis metabolism, were significantly inhibited in the 6% SP supplementary group (P<0.05). At the end of the 8-week feeding trial, a challenge test of intraperitoneal injecting 50% CCl₄ solution was performed. It was found that the cumulative mortality rate of the 2% SP supplementary group was lower than that of the control group at 96 h post-injection. Further analysis of hepatic antioxidant capacity at 24 h post-injection revealed that the hepatic SOD activity of the 2% SP supplementary group was significantly higher than that of the control group (P<0.05). In general, the supplementation of 2% S. perfoliatum in diet showed no negative effect on the growth and feed utilization of juvenile M. amblycephala, but improved the intestinal antioxidant capacity. 4% and 6% dietary supplementation levels of S. perfoliatum inhibited the growth and resulted in fat deposition in the muscle. All the results of this study provide a reference for further application of S. perfoliatum in aquatic feed.

Abstract:In recent years, searching for suitable feed additives to promote the growth, metabolism, and antioxidant capacity of aquatic animals has become an inevitable task for the aquaculture industry. The purpose of this trial was to study the effects of dietary bile acid (BAs) on growth performance, body composition, serum biochemical indexes, as well as liver and intestinal health of Monopterus albus. 1 200 eels (23.00±0.05) g were randomly divided into 5 groups with 4 replicates in each group. The fish in the five groups were fed isonitrogenous diets supplemented with 0, 125, 250, 375 and 500 mg/kg BA, and named as CON, BA125, BA250, BA375 and BA500 groups, respectively. The results of the 56-day feeding experiment showed that as the amount of BA increased, the final average weight, weight gain rate, and specific growth rate first increased and then decreased, with significantly higher figures in the BA250 group compared to the CON and BA500 groups. The feed conversion ratio showed a trend of first decreasing and then increasing. The crude protein content in whole body increased firstly and then decreased, while the trend for crude lipid content in liver was the opposite. The activity of serum glutamic pyruvic transaminase in the CON group was significantly higher than in the other groups, while the activity of glutamic oxaloacetic transaminase showed a trend of first decreasing and then increasing. The content of D-lactic acid decreased gradually, while diamine oxidase activity decreased at first and then increased. Compared with the CON group, the liver structure of the BA125 and BA250 groups was more intact. Excessive BA (BA375, BA500 groups) caused vacuolation and rupture of hepatocytes. The number of lipid droplets in liver decreased at first and then increased. The mRNA expression levels of acc and dgat2 in the liver showed a decreasing trend, while the mRNA expression level of cpt1 first increased and then decreased, and the mRNA expression level of pparα was highest in the BA375 group. The intestinal villus width and muscle layer thickness increased at first and then decreased, but the villus height and villus width in BA500 group were significantly lower than those in CON group. The total superoxide dismutase activity in the liver showed a gradual upward trend, with the highest glutathione peroxidase activity and catalase activity in the BA250 group, and the lowest malondialdehyde content in the BA250 group. The activities of total superoxide dismutase and glutathione peroxidase in the intestine both showed a trend of increasing first and decreasing afterwards, while the trend of malondialdehyde was the opposite, with the BA250 group significantly lower than the CON and BA375 groups. The mRNA expression levels of the intestinal tight junction protein genes zo1, zo2, and occludin all showed a significant trend of increasing first and then decreasing. The study showed that the addition of appropriate amounts of BA to the feed can improve the growth performance of Monopterus albus, enhance the antioxidant capacity of the liver and intestine, reduce lipid deposition in the liver by increasing lipid catabolism and inhibiting lipid synthesis, and alleviate liver damage and improve liver and intestinal function. The suitable dietary addition amount of BA in M.albus is 250.0-283.3 mg/kg.

Abstract:In order to explore the effects of feeding different diets on pond water quality, growth, nutritional quality and serum biochemical indexes of Scylla paramamosain in saline-alkali water pond, this experiment was set up with three biological bait groups and one artificial compound feed group, namely, Mactra chinenesis, Synechogobius hasta and Trachypenaeus curvirostris. Three replicates were set in each group, and the experimental period was 4 months. The changes of pond water quality in each group were analyzed, and the growth, nutrition and serum biochemical indexes of crabs in each group were compared by One-Way ANOVA. The results show the following. The differences of water temperature, salinity and pH in each group were small, but the differences of dissolved oxygen, ammonia nitrogen and nitrite nitrogen were large. Among them, dissolved oxygen in the S. hasta group decreased from 11.5 to 9.2 mg/L, while ammonia nitrogen and nitrite nitrogen increased from 0.44 mg/L and 0.022 mg/L at the beginning of culture to 0.89 mg/L and 0.050 mg/L at the end of culture, respectively. The crab weight (334 g), weight gain rate (332.7%) and specific growth rate (0.076%/d) were significantly higher in the M. chinenesis group than in the other groups. The survival rate of artificial compound feed group was the highest, reaching 66.67%. The fatness (0.221 g/cm³) in the group of S. hasta was significantly higher than that in other groups. The content of valine, methionine, isoleucine and phenylalanine in the essential amino acids of crab muscles and the total hepatopancreas taste-presenting amino acids and total fresh taste amino acids in the M. chinenesis group were the highest among all groups. The contents of threonine, leucine, lysine and histidine in the essential amino acids of hepatopancreas in the artificial diet group were the highest among the three groups. The total amount of savory amino acids and umami amino acids in muscle of T. curvirostris group were the highest among all groups. The contents of saturated fatty acids, polyunsaturated fatty acids and fatty acids in muscle and hepatopancreas were the highest in the M. chinenesis group. The total protein content in the M. chinenesis group was significantly higher than that in other groups. The total cholesterol in the S. hasta group was significantly higher than that in other groups. The aspartate aminotransferase, triglyceride and glucose in the artificial compound feed group were significantly higher than those in other groups. Correlation analysis showed that there was a significant positive correlation between the routine nutrients of biological diets such as M. chinenesis and the growth indexes of S. paramamosain. The results of the study showed that the M. chinenesis group had significant advantages in growth, nutrition and serum protein indexes, which could be used as palatable diet for breeding S. paramamosain in saline-alkali ponds. This study provides data reference for the cultivation and popularization of S. paramamosain in saline-alkali water ponds in northern China.

Abstract:Chitosan oligosaccharide (COS) is a potent immunopotentiator, but rarely used in aquaculture. The aim of this study is to investigate the effect of feeding COS intermittently on growth, non-specific immune indices, digestive enzyme activities, histological and disease resistance of sea cucumber Apostichopus japonicus. A. japonicus [mean body weight (18.51±0.28) g] were first fed for 8 weeks by two groups (control group, A. japonicus were fed with basal diet; treatment group, sea cucumbers were first fed with basal diet added 0.5% COS for 1 day and then fed with basal diet for 2 days). Growth performance, non-specific immune enzyme activities, intestinal enzyme activities, the structure of the respiratory tree, intestines，expression of intestinal immune gene and immune response were measured to investigate the effects of feeding frequency with COS once every 3 days of sea cucumber A. japonicus. The results indicated that treatment group had significantly higher ratio of visceral weight to body wall weight (VBR) and ratio of intestine weight to body wall weight (IBR) (P<0.01). Phagocytic activity and respiratory outburst of coelomocytes in treatment group were significantly higher than those in control group (P<0.05). The activities of enzymes such as acid phosphatase (ACP), falkaline phosphatase (AKP), lysozyme (LZM) and total nitric oxide synthase (T-NOS) of intestine in treatment group increased significantly (P<0.01) and the activities of AKP and LZM of intestine in treatment group increased by 70.06% and 156%, respectively. The mRNA relative expression of Aj-lyz gene (P<0.01) of intestine in treatment group were significatly higher than that in control group, and the relative expression level of Aj-lyz gene of intestine in treatment group increased by 22.04%, respectively. The activity of catalase (CAT) of coelomocytes in treatment group was significantly higher than that in control group (P<0.01), but the content of malondialdehyde (MDA) of coelomocytes and intestine showed no significant difference between the two groups (P>0.05). Compared with the control group, the muscularis and serosa in foregut, fold height and fold width in midgut and hindgut were significantly increased in treatment group (P<0.01). We found that the survival rate of the sea cucumber A. japonicus against infection with Vibrio splendidus was higher in the treatment group, with a relative protection rate of 66.67%. Above all, the feeding frequency of once every 3 days for COS is recommended to promote the growth performance, non-specific immunity and immune response of the A. japonicus. This study provides theoretical support for follow-up research.

Abstract:Scuticociliatia disease is a major threat to large yellow croaker Larimichthys crocea at the fry stage. In the previous study, a ubiquitin regulatory X domain-containing protein (UBXN1) gene was found to be involved in Scuticociliatia disease resistance through genome-wide association analysis. To further confirm its gene function in resistance against Scuticociliatia, we identified UBXN1 gene sequence and investigated its expression characteristics, as well as signal pathway. The complete cDNA sequence of UBXN1 was 915 bp, encoding 304 amino acids. The putative UBXN1 protein was evolutionarily conserved and contained a UBA and a UBX domain. Moreover, UBXN1 had varying degrees of expressions in different tissues, among which the highest expression was observed in brain, moderate expression was in liver, heart and kidney, and the lowest expression was in muscle by qRT-PCR detection. It also showed that induced expression was found in spleen, brain, liver, and kidney during the early phase of infection, and the expression gradually recovered to the control level at the late phase. Further subcellular localization analysis showed that UBXN1 uniformly distributed in cytoplasm and nucleus. In addition, 16 differentially expressed genes were found in a comparative transcriptome analysis between the UBXN1 over expression group and control vector group, including up-regulated genes RPL41/RPL39/XIST/RNA45SN4 and down-regulated genes ATP8/ND4L. These findings provide new insights into finfish UBXN1 and its potential regulatory signaling pathway.

Abstract:Interferon regulatory factor 3, a member of the interferon regulator factor (IRF) family, are major transcriptional regulators of type I interferon-dependent immune responses and play an important role in innate immune responses against DNA and RNA viruses. In this study, The irf3 gene (interferon regulatory factors 3, Opirf3) was obtained from the Oplegnathus punctatus genome database, and analyses found that the CDS sequence of Opirf3 has a total length of 1 362 bp, encoding 453 amino acids. The molecular weight of predicted protein is 50.0 ku, the theoretical isoelectric point is 4.97, and has an IRF domain and an IRF-3 domain. RT-PCR showed that Opirf3 was expressed in liver, gills, heart, skin, spleen, intestine, brain, kidney, stomach and head kidney of O. punctatus. When the fish were infected with SKIV-SD for 7 days, the expression levels of Opirf3 in the liver, spleen and kidney of immune tissues were significantly upregulated. In vitro stimulation experiments of the kidney cell line of O. punctatus showed that the expression of Opirf3 was significantly upregulated after stimulation with different concentrations of poly I:C, and the relative expression level of Opirf3 was the highest at a concentration of 100 μg/mL, which was 87.9 times higher than that of the control group. After siRNA interference, the expression level of Opirf3 was significantly reduced by 30%, the Opirf3 related genes IFN-α, CD40, CD80 and IL-1β were significantly downregulated, and IL-6 was significantly upregulated. These results may indicate that the Opirf3 gene is involved in the innate immune response of type I IFN in the resistance to SKIV-SD of O. punctatus. This study can provide a theoretical basis for the molecular breeding of disease resistance of O. punctatus.

Abstract:Haemorrhagic gill necrosis disease (HGND) has become one of the important epidemic diseases of cultured American eels. In previous studies, American eel adomavirus (AEAdoV) was isolated from eel with HGND. In order to establish a PCR and real-time fluorescence quantitative PCR (qPCR) method for the detection of the virus, primers were designed according to the superfamily 3 helicases (S3H) sequence of AEAdoV-FJ. Further evaluations on the sensitivity, specificity, repeatability, and application effect of this method were conducted. The results showed that the established PCR method could specially amplify a 300 bp band, which was cloned and used to construct plasmid standards for qPCR; the cycle threshold value (C_t) of qPCR and the copy number of the standard sample had a consistent relationship with a wide range. The obtained correlation coefficient (R²) of the standard curve reached 0.999, and the amplification efficiency was 105.067%. The qPCR method could detect a minimum of 10 viral copies with higher sensitivity than routine PCR method. Both methods could specifically detect AEAdoV with negative amplification reaction on Rana grylio virus (RGV), Anguillid herpesvirus (AngHV), Koi herpesvirus (KHV), White spot syndrome virus (WSSV), Japanese eel adomavirus (JEAdoV), and Marbled eel adomavirus (MEAdoV). The coefficient of variation within and between groups of this method were both less than 2%, suggesting good repeatability. Further application results showed that the detection rate of AEAdoV from 35 samples of American eels with HGND by routine PCR and qPCR was 82.8% and 97%, respectively, indicating that the virus is prevalent among the diseased eels. Analysis of the virus quantity of the eel tissues indicated that the level of AEAdoV was relatively higher in heart, liver, gill and fin, and lower in mucus, skin and spleen. These results indicate that routine PCR and qPCR assays with high sensitivity and specificity for detection of AEAdoV have been established, and confirm that AEAdoV is closely related to HGND and exists in the main organs of infected eels. This study will be valuable for further investigations of the correlation between AEAdoV and HGND, and helpful for understanding the epidemic and etiology of AEAdoV.

Abstract:The protein from marine fish is regarded as an ideal resource of high-quality protein thanks to their high nutritional value and good digestibility. The application of fish protein in infant rice flour products can not only give the product a richer flavor, but also improve the nutritional value of the product and meet the nutritional requirements of infants. To further expand the application of marine fish protein in food products, the enzymatic modification of blue round scad (Decapterus maruadsi) protein isolate was carried out to obtain blue round scad protein isolate hydrolysate (BPIH) with good solubility. The inhibitory effects of BPIH on short-term retrogradation of rice starch (RS) was investigated. The enzymatic modification process was optimized by response surface methodology, and was added to RS at concentrations of 3%, 6% and 9% (W/W). The measurements of coagulability, dynamic viscoelasticity, and thermal properties and microstructure of RS were carried out to evaluate the anti-retrogradation activities of BPIH. The results showed that the optimal conditions determined by response surface methodology were: enzyme bottom ratio of 5 000∶1 (U/g), enzymatic digestion time of 3 h, feed-to-liquid ratio of 1.00∶3.81, enzymatic digestion temperature of 46.36 ℃, and enzymatic pH of 6.30. The actual value of nitrogen solubility index (NSI) was 85.41%±0.82%, which was close to the predicted value of 86.37%. The degree of BPIH hydrolysis reached 21.62% under these enzymatic conditions. The peptides less than 1,000 u in BPIH accounted for 79.94%, which were mainly small oligopeptides. The addition of BPIH attenuated the coagulation phenomenon of RS, reduced the energy storage modulus (G') of RS during storage at 4 ℃, and significantly reduced the peak temperature (T_p) and enthalpy (ΔHr) of RS after aging (P<0.05); the rice starch added with BPIH had larger pores in the microstructure after aging, which enhanced the ability of starch to retain internal water after pasting. These results indicate that BPIH can inhibit the formation of gel network and microcrystalline structure of RS during storage at 4 ℃, and may also limit the aggregation between starch molecules and inhibit or delay the short-term aging of RS. The present study provides a theoretical reference for the application of the enzymatic hydrolysate of blue round scad protein isolate in food protein ingredients.