Abstract:Glutathione S-transferase (GSTs, EC 2.5.1.18), a class of multifunctional detoxification enzymes widely distributed in organisms, is involved in the metabolism of many toxic substances from both internal and external sources, and plays an important role in protecting cells against biological and abiotic stresses. This study investigated the characteristics of the Ruditapes philippinarum gene family (RpGST) and its function in response to acute hypersalinity and acute hyposalinity stress. Bioinformatics methods were used to identify RpGST gene family members and analyze their structural characteristics, chromosome localization, phylogeny, and expression characteristics in the hepatopancreas after acute salt stress. A total of seven RpGST genes were identified, namely GSTA1, GSTA2, GSTA3, GSTA4, GST_C_3a, GST_N_M1, and GST_N_M2. Chromosome localization results revealed that these seven GST genes were located on five chromosomes. The hydrophobicity analysis showed that all protein members had different degrees of hydrophilicity. The average aliphatic amino acid index was 82.08; subcellular localization found that RpGST proteins were all located in the cytoplasm; and all members of this gene family possess the glutathione transferase domain (PF00043, PF02798), which is associated with antioxidant and detoxification functions. Phylogenetic analysis revealed that RpGSTs were divided into three subfamilies and were evolutionarily conserved. The seven RpGSTs were divided into three distinct classes, with the GSTA class being the largest, consisting of four members within the Ruditapes philippinarum family, whereas the GSTM class consisted of two members and the GST_C_3 class of one member. All GSTs in the Ruditapes philippinarum family evolved into separate clusters, such as RpGSTA and RpGSTM, related to the wide distribution and strong adaptability of the family. These results can provide a reference for the subsequent breeding of Ruditapes philippinarum with high and low salinity tolerance. After acute salinity stress in Ruditapes philippinarum for 0 h, 12 h and 24 h, the hepatopancreatic expression levels of RpGST members in acute hypersaline (40) and hyposaline (15) stress were detected by qRT-PCR. The results evidenced that the relative expression levels of RpGSTA1, RpGSTA2, RpGST_N_M1, and RpGST_N_M2 in the hepatopancreas of Ruditapes philippinarum increased with time, and the expression levels of RpGSTA1 and RpGSTM2 were significantly different from those of the control group (P＜0.01), whereas the relative expression levels of RpGSTA3, RpGSTA4 and Rp GST_C_3a first decreased and subsequently increased. The relative hepatopancreatic expression levels of RpGSTA1, RpGSTA4, RpGST_C_3a, RpGST_N_M1, and RpGST_N_M2 in Ruditapes philippinarum increased over time under acute hyposaline stress. Specifically, those of RpGSTA1 and RpGSTA4 significantly changed during acute hyposaline stress, gradually increasing with time, and this difference was significant compared with the control group (P＜0.05). In contrast, the relative expression levels of RpGSTA2 initially decreased and subsequently increased over time, while the relative expression of RpGSTA3 first increased and then decreased. The expression of glutathione transferase under acute low-salt stress was significantly higher than that under acute high-salt stress, indicating that acute low-salt stress had a more pronounced effect on Philippine clams than acute high-salt stress. This study clarified the gene characteristics, phylogeny and response mechanism of the RpGST gene family in the context of acute hypersaline and hyposaline stress. It enriches the research data on the RpGST gene family in bivalve shellfish and provides a reference for further study on the role of this gene family in regulating salinity stress.

Abstract:Proteins, lipids, and carbohydrates are essential nutrients and main energy sources for the growth and development of organisms. When dietary protein is excessive, it is metabolized as energy, which not only increases the organism’s metabolic burden, affecting normal growth, but also causes water pollution through the discharge of waste products such as ammonia nitrogen. Reasonable use of lipids and carbohydrates can improve the utilization of dietary protein, save breeding costs, and promote the growth of aquatic animals. To explore the effects of different energy sources and dietary levels on the growth performance of Litopenaeus vannamei, we prepared a control diet (C) with 37% protein content and a protein-energy ratio of 20.23 mg/kJ. Four experimental diets were formulated to investigate the effects of different energy sources and levels on L. vannamei growth. These diets had protein-energy ratios of 19.51 mg/kJ (medium carbohydrate group, MC), 18.85 mg/kJ (high carbohydrate group, HC), 19.45 mg/kJ (medium lipid group, ML), and 18.54 mg/kJ (high lipid group, HL). These ratios were prepared by increasing the dietary energy content through carbohydrates or lipids. Juvenile shrimps, initially weighing (0.6±0.02) g, were fed these diets for 56 days under freshwater conditions. Before the end of the experiment, the shrimps underwent a 24-hours fast, followed by weighing and counting after removal from the net cage to calculate the survival rate, weight gain rate, specific growth rate, feed coefficient, protein efficiency ratio, and protein deposition rate. The muscle and hepatopancreas were collected from six shrimps in each cage to assess muscle composition, digestive enzymes (protease, lipase, and amylase), and antioxidant enzyme activities (T-AOC, MDA, and CAT). Serum samples were collected from 12 shrimps from each cage to determine serum biochemical indexes (GOT, GPT, and TG), serum antioxidants, and non-specific immune indexes (T-AOC, MDA, and AKP). The results evidenced that, compared with the control group, increasing dietary lipid levels significantly increased the growth performance and protein deposition rate of shrimp (P＜0.05). The HL group exhibited the highest specific growth rate and protein deposition rate. Conversely, increasing dietary carbohydrate levels did not significantly affect shrimp growth and protein deposition rate (P＞0.05). These results indicate that L. vannamei has a strong ability to utilize dietary lipids, and increasing dietary lipid levels can significantly improve both growth performance and the utilization of dietary protein in L. vannamei. Conversely, increasing dietary carbohydrate levels has limited effects on the growth and dietary protein utilization of L. vannamei. In terms of muscle composition, compared with the control group, the ML, MC, and HC groups evidenced significant increases in crude protein content (P＜0.05), while the HL group displayed a slight increase in crude protein content compared with the control group, although this difference was not significant (P＞0.05). The total lipid content in shrimp muscle increased significantly with the rise in dietary energy levels in all groups (P＞0.05). The ML, HL, MC, and HC groups all demonstrated significantly higher protease and lipase activities in the hepatopancreas compared with the control group (P＜0.05). The hepatopancreas amylase activity of shrimp in MC and HC groups was significantly higher than that in the control group (P＞0.05), but no significant difference was observed in the activities of amylase in the hepatopancreas of ML and HL groups compared with the control group (P＞0.05). Increasing dietary lipid levels led to a significant rise in the activity of serum GPT and TG contents (P＜0.05). In addition, HL group demonstrated significantly higher serum GOT activity than the control group (P＜0.05). Increasing dietary carbohydrate levels also significantly increased serum GPT and TG (P＜0.05), but had no significant effect on serum GOT (P＞0.05). At the same protein level, ML and HL groups exhibited significantly higher serum and hepatopancreatic MDA levels than the control group (P＜0.05), while MC and HC groups also had significantly higher serum and hepatopancreatic MDA levels than the control group (P＜0.05). In HC and HL groups, AKP activity was significantly higher than that in the control group (P＜0.05). Compared with the control group, increasing dietary lipid levels significantly increased the serum and hepatopancreatic T-AOC in shrimp. Increasing dietary carbohydrate levels also elevated the T-AOC in the serum but evidenced a trend of initially increasing and then decreasing in the hepatopancreas (P＜0.05). CAT activity exhibited a trend of initially decreasing followed by an increase compared with the control group (P＜0.05). These results suggest that shrimp fed a diet with a lipid content of 9.59% and a protein-energy ratio of 18.54 mg/kJ exhibited the best growth performance under the experimental conditions. Lipids, as a dietary energy source, are more suitable for L. vannamei than carbohydrates.

Abstract:The aim of this experiment was to investigate the effects of high-fat diets on the short-term growth performance and antioxidant capacity of pearl grouper to help formulators and farmers anticipate the possible negative effects of high-fat diets on grouper growth and take effective measures in the formulation and feeding schedule of high-fat diets. Seven groups of isonitrogenous diets with fat levels of 8% (EE8), 10% (EE10), 12% (EE12), 14% (EE14), 16% (EE16), 18% (EE18), and 20% (EE20) were fed to pearl grouper (initial mean weight: 13.70±0.01g) for 4 weeks with a crude protein level of 48%. The experimental results showed no significant change in weight gain rate (WGR) and survival rate (SR) as the level of dietary ether extract increased (P＞0.05), while the feed intake was significantly lower in the EE14-EE20 group (P＜0.05); further, the viscerosomatic index (VSI) and protein efficiency ratio (PER) increased significantly (P＜0.05) after the dietary ether extract exceeded 16%. The EE14-EE20 group had a significantly higher abdominal muscle ether extract (AMEEC) (P＜0.05), and the EE16-EE20 group had a significantly greater hepatosomatic index (HSI) (P＜0.05). Compared to the EE12 group, total cholesterol (T-CHO) was significantly higher in the EE8, EE10, EE18, and EE20 groups (P＜0.05); glutathione peroxidase (GSH-PX) activity was significantly lower in the EE16-EE20 group (P＜0.05); malondialdehyde (MDA) content was significantly higher in the EE20 group (P＜0.05); and vacuolated area and hepatocytes in the EE8 and EE16-EE20 groups’ lipid droplet amount were significantly increased (P＜0.05). The relative expression of the lipid synthesis genes g6pd, 6gpd, and me was significantly increased in the EE20 group (P＜0.05), and the lipolytic genes cpt-1 and pparα were significantly increased in the EE16-EE20 group (P＜0.05). The results have shown that dietary ether extract above 16.77% causes fatty deposits in the liver of pearl amberjack, reducing the liver’s antioxidant capacity and impairing liver health.

Abstract:In sturgeon aquaculture, abnormal growth variations among fish in the same pond frequently result in decreased yields. The gut microbiota, a crucial component of the digestive system, plays a pivotal role in growth performance of these fish. Currently, there is limited research on the relationship between gut microbiota and individual growth differences in sturgeon. The objective of this study was to examine the characteristics of the gut microbiota in populations of Huso dauricus and Acipenser schrencki in which growth rate differences exceeded 50% of body weight. The fish were bred at the same time and under identical conditions. The aim was to uncover the relationship between sturgeon growth rate and the composition of the gut microbiota. The results revealed notable differences in gut microbiota diversity and composition between H. dauricus and A. schrencki, as well as among different populations in both species. In the fast-growing population of H. dauricus (LH), the dominant genus in the gut was Sphingomonas (67.0%), whereas in the slow-growing population of the same species (SH), the dominant taxa were Sphingomonas (29.5%) and Clostridium sensu stricto 1 (54.2%). In the fast-growing population of A. schrencki (LA), the dominant genera in the gut were Sphingomonas (33.5%) and Cetobacterium (38.1%), whereas in the medium-growing population of the same species (MA), the dominant taxa were Sphingomonas (42.6%), Clostridium sensu stricto 1 (14.3%), and Cetobacterium (33.0%). Sphingomonas and Clostridiaceae were the primary discriminatory taxa in the gut microbiota of sturgeon exhibiting varying growth rates. In conclusion, species-specific variations were evident in the diversity and composition of the gut microbiota in sturgeon. Genetic factors play a crucial role in shaping and selectively altering the gut microbiota in animals, including fish. Moreover, each individual fish harbors a distinctive ecosystem within its gut, which is influenced by genetic factors and contributes, to some extent, to the determination of the types and quantities of gut microbiota. There is evidently a close relationship between the gut microbiota and fish growth, as the gut microbiota directly or indirectly impacts the growth rate of the fish through its involvement in digestion, immunity, and metabolism. In particular, Sphingomonas and Clostridiaceae may exert a pivotal influence on sturgeon growth rates. These findings provide initial insights into the link between the gut microbiota of sturgeon and growth rates, offering a theoretical foundation for the precise modulation of the intestinal microbiota to attain rapid growth of sturgeon in aquaculture.

Abstract:Fish is the primary focus of research within fishery resources and represents one of the most important sources of human food. Within the fishery ecosystem, the fish community can reflect the energy conversion processes. The southern Yellow Sea, characterized by the interplay of the Yellow Sea warm current, coastal current, and the Yellow Sea cold water mass, possesses a complex ecological environment and abundant fish resources. To comprehend the composition and characteristics of the fish community and the spectrum of fish biomass particle sizes in the southern Yellow Sea, we conducted an analysis using trawl survey data from 2017 to 2018. Our study examined fish species composition, dominant species, and resource density across four seasons and constructed a fish biomass particle size spectrum. The findings revealed that a total of 133 fish species from 64 families and 20 orders were collected. The dominant species included Larimichthys polyactis, Pampus argenteus, Engraulis japonicus, and Trichiurus lepturus, with some differences in dominant species across different seasons. The annual average resource density of fish was (1258.85±796.92) kg/km² , with seasonal variations observed in summer, spring, autumn, and winter. An ABC curve indicated significant disturbance in fish communities during spring and autumn, with moderate disturbance during summer and winter. Notably, distinct seasonal differences were found in the Sheldon-type particle size spectrum of fish, with high abundance among small-sized individuals at specific particle size levels corresponding to peaks. Furthermore, the fitting curve for the standardized fish biomass particle size spectrum exhibited a parabolic shape with curvatures higher than the stable theoretical value –1. This suggests dominance by small individuals within the fish community and low nutrient cycling efficiency. Overall, the instability of the fish community in the southern Yellow Sea may be attributed to environmental factors, the physiological habits of fishes, and human fishing practices.

Abstract:The Myctophidae family is widely distributed in mesopelagic oceans worldwide and plays a significant role in the pelagic food chain due to its vertical migratory behavior. Myctophidae are diverse and the morphological differences between genera are not obvious. Therefore, the use of molecular markers for Myctophidae identification would be advantageous. In this study, we amplified 56 Myctophidae samples collected from the Northwest Pacific using the Cyt b and 12S rRNA genes. These amplified sequences were subsequently used for phylogenetic analyses alongside sequences from 29 other Myctophidae species in 18 genera from the GenBank database. We explored the applicability of Cyt b and 12S rRNA genes for identifying Myctophidae species. The results indicate that the 56 samples belonged to 6 species: Ceratoscopelus warmingii, Symbolophorus californiensis, Myctophum asperum, Tarletonbeania crenularis, Notoscopelus japonicus, and Notoscopelus sp. The intra-specific and inter-specific genetic distances based on the Cyt b gene were more pronounced than those based on the 12S rRNA gene. The difference between the average inter-specific and intra-specific genetic distances of Cyt b and 12S rRNA gene was 25 and 26, respectively. These results indicated that both genes meet the basic requirements for DNA barcodes. Phylogenetic analysis evidenced that the six Myctophidae species each formed an independent clade based on Cyt b and 12S rRNA gene sequences. However, in the evolutionary tree constructed based on the Cyt b gene, each fish clustered more closely with sequences in the GenBank database. In summary, both Cyt b and 12S rRNA genes could be used as DNA barcodes for identifying Myctophidae species, amd the Cyt b gene was particularly suitable for analyzing phylogenetic relationships.

Abstract:With the construction and operation of water infrastructure in river basins, significant alterations have occurred in the original habitats, leading to changes in the patterns of juvenile fish resources and the spatial distribution of fish spawning grounds. As a result, considerable attention has been devoted to studying the patterns of juvenile fish resources and the characteristics of spawning grounds in various sections of the Yangtze River mainstream. The dam downstream area has emerged as a focal point for investigating fish spawning habitats. However, due to constraints such as hydrological conditions and topography, localized studies on the spatiotemporal patterns of fish spawning and early life stages in the dam downstream area have been challenging. Extensive research has been conducted on the dynamics of fish community structure in the middle and lower reaches of the river, as well as the interconnected lakes, encompassing changes in fish populations and the mechanisms driving river-lake migrations. However, limited research is available on the coupling relationship between concentrated spawning habitats, fish resources early in their life cycle, and river environments in the upstream tributaries of lakes. Exploring the patterns of early-stage fish resources and concentrated spawning in the upstream tributaries of large lakes is equally important for the conservation of aquatic fisheries resources. The upstream rivers of lakes serve as crucial ecological zones for migratory fish reproduction in river-lake systems and play a vital role in replenishing juvenile fish resources for such species. The Xitiaoxi River, an important supplementary tributary of the Tai Lake, also serves as a crucial conduit for fish migration in the southern the Tai Lake basin. It is home to a nationally protected gene pool and boasts abundant fish resources. The East Mountain section below the Jiangdong Power Station in the Xitiaoxi River is a concentrated breeding site for regional fish populations. Moreover, the area downstream of the Jiangdong Power Station provides favorable hydrological and topographical conditions, making it an ideal location for conducting localized studies on the spatiotemporal patterns of juvenile fish resources. To investigate the intrinsic relationship between the variables of the downstream river habitat and fish resources under the influence of the power station, this study conducted a 90-day survey of fish resources and spatial-temporal patterns using a shallow type I plankton net in the Dongshanjiang section of the Xitiaoxi river from April to July 2022. The survey obtained 24455 fish eggs and 24325 larval fish, with a daily average density of (0.5±0.7) ind/m³ and (0.5±0.6) ind/m³, respectively. Using morphological and molecular biology methods for identification, a total of 35 fish species were identified, belonging to four orders, 14 families, and 22 genera. Hemiculter bleekeri, Squalidus argentatus, Cyprinus carpio, Carassius auratus, Saurogobio dabryi, and Culter mongolicus had relatively high numbers of eggs and larvae. The fish resources included 9 species of benthic egg-laying fish, 5 species of pelagic egg-laying fish, 9 species of adhesive egg-laying fish, and 12 species of drifting egg-laying fish. Late May, early June, and late June were the peak spawning periods. The sampling results evidenced that benthic and adhesive egg-laying fish, which use aquatic plants as attachment substrates, were dominant on the left and right bank sample lines, whereas drifting, adhesive, and pelagic egg-laying fish dominated the river center sample line. The redundancy analysis results evidenced that water temperature, flow rate, and water level influenced the number of fish eggs and larvae in the area to varying degrees, with water level and flow rate being the main factors affecting fish reproduction, and egg production increasing significantly after rainfall. Based on the results of egg harvest and egg development stage, the sampled river section and the upstream river of Dongshanjiang in the Xitiaoxi River were determined to be a composite fish spawning ground. The fish resources in this spawning ground were abundant, and the habitat was suitable for fish reproduction and nurturing. The discharge of the power station had a certain effect on fish reproduction, and moderate ecological scheduling could meet the needs of fish reproduction, which was of great significance for the protection of fish diversity and fishery resources in the Tai Lake.

Abstract:There is relatively little information on the biology of Indian Ocean albacore tuna (Thunnus alalunga); further, many problems with the fishery data result in a large uncertainty in its stock assessment results and affect fishery management. In this study, based on the fishery catch, standardized Catch Per Unit Effort (CPUE) data, and relevant stock hypotheses of Indian Ocean albacore tuna, a Bayesian biomass dynamic model was used to conduct a stock assessment. The results showed that: (1) The observation error of catch has an important influence on the estimation of model parameters, judgment of resource status, and fishery management, and an increase in catch observation error increases the probability of overfishing assessed by the model, which leads to a decrease in Total Allowable Catch (TAC); (2) The shape parameters of biomass dynamic model, prior distribution of r, and choice of resource abundance index affect the quality of stock assessment, and this study shows that the stock assessment results of the Fox model are more reasonable than those of the Schaefer model, the increase in the range of r priori distribution makes the resource state assessed by the model better, and the assessment results are relatively better when using the standardized CPUE of the southwest waters; (3) Setting a range of resource proportions (φ、P₂₀₁₇) for certain years can help improve the quality of fishery stock assessment under the lack data; (4) The probability of overfished and overfishing for albacore tuna in the Indian Ocean are 34% and 50%, respectively, and the probability of both occurring simultaneously is 32%, and the species is at risk of overfishing. The projection analysis showed that the probability of not overfishing for Indian Ocean albacore tuna after 10 years was greater than 60% when the TAC was controlled below 32658 t (i.e., 90% of the final five-year average catch). The Bayesian biomass dynamic model, as a data-limited fishery stock assessment model, is applicable to Indian Ocean albacore tuna, and it can better consider the effects of parameter inputs and uncertainty factors on the quality of stock assessment and the estimation of TAC, providing a scientific basis for an in-depth study of the stock status and management of Indian Ocean albacore tuna.

Abstract:To study the position and role of Miichthys miiuy in the food web of Zhoushan fishing ground ecosystem, we collected a total of 727 Miichthys miiuy samples monthly from August 2021 to June 2023 on Zhoushan fishing ground, and examined the feeding habits based on both stomach content analysis method and carbon and nitrogen stable isotope techniques. The results indicated that the main prey species of Miichthys miiuy in Zhoushan fishing ground were Pisces, Decapoda, Stomatopoda, Lamellibranchia, Cephalopoda, and Brachyura. Harpodon nehereus, Collichthys lucidus, Coilia mystus, and Amblychaeturichthys hexanema were the dominant prey species. The δ¹³C of Miichthys miiuy ranged from –19.09% to –13.04‰, with an average value of –(16.74±1.03)‰, which was negatively correlated with body length (P＜0.01). The value of δ¹⁵N was between 10.72% and 15.96‰, with an average value of (12.44±1.36)‰, which was significantly positively correlated with body length (P＜0.01). The trophic level of Miichthys miiuy on the Zhoushan fishing ground, calculated from δ¹⁵N values, ranged from 3.93 to 4.92, with an average trophic level of 4.30±0.39, and the trophic level was significantly positively correlated with body length (P＜0.01). The stable isotope analysis revealed that Stomatopoda made the highest contribution to Miichthys miiuy trophic level (20.6%), followed by Cephalopoda (18.3%), Decapoda (16.4%), and Lamellibranchia (13.7%). Miichthys miiuy fed throughout the year, and feeding intensity varied significantly with season and body length. Seasonally, the stomach fullness index was the highest in winter and the lowest in autumn; in terms of body length, the stomach fullness index was low for large individuals and high for small individuals. The empty stomach rate was the highest in autumn and the lowest in winter. The empty stomach rate did not significantly vary with body length. These results will help to understand the feeding habits of Miichthys miiuy on Zhoushan fishing ground and provide basic information and scientific basis for the study of food web dynamics and trophic dynamics.

Abstract:Codend size selectivity is the keystone for management of trawling fisheries and sustainable exploitation of fisheries resources. In order to assess the size selectivity of trawl codends, experimental sea trials are often conducted and fishing data is manipulated using some mathematical models to obtain selectivity parameters, such as 50% retention length (L50) and selection range (SR), and selectivity curves. Providing the values of this information, however, is highly inadequate. It needs to account for the uncertainties in size selectivity and represent them in confidence intervals. To do this, the double-bootstrapping technique is intensively applied in fishing gear selectivity studies. In this study, the basic principle of the double-bootstrapping technique was firstly introduced, then two set of fishing data involved two different fishing species were used as case studies to show and compare how this technique was used to estimate the uncertainties of codend size selectivity. Our results demonstrated that the uncertainties of codend size selectivity could be easily estimated applying the double-bootstrapping technique. Additionally, the most commonly wrong practice of using the doublebootstrapping technique was discussed. Our study will provide a guideline for conducting trawl codend selectivity studies, improve the level of selectivity researches, and contribute to the sustainable development of marine fisheries in China.