Abstract:Siniperca chuatsi is an economically important freshwater fish in China that prefers to hide near stones or lush grass at the bottom of water bodies. The back and body sides were yellow with dark brown markings, with a white abdomen. Such a unique skin pattern is conducive to hidden predation and avoiding enemies. Research on the formation of different color patterns in mandarin fish skin is mainly based on observing the types and distribution of pigment cells, while research on the corresponding molecular regulation mechanism is relatively scarce. In recent years, omics technology has been applied to the study of fish body color patterns, which can identify candidate pathways and genes related to body color formation. The complex body color pattern of Siniperca chuatsi has ecological significance and economic value. To explore the molecular mechanism of the color pattern formation of Siniperca chuatsi, transcriptome analysis was carried out on the pattern area, non-pattern area, and abdominal skin of the body side of Siniperca chuatsi. The expression changes of tyrosinase family genes in Siniperca chuatsi from the embryo to 30 dph were determined using fluorescence quantitative PCR; this showed that the differentially expressed genes between the three skin regions were mainly enriched in ECM-receptor interaction, tight junction, adhesion, and other pathways, and the MAPK pathway was the core pathway. The expression of tight junction protein 1a (tjp1a) in the non-patterned area was significantly higher than in the patterned and abdominal areas. The expression levels of tyrosinase-related protein 1 (tyrp1), dopachrome tautomerase (dct), and melanocyte-inducing transcription factor a (mitfa) in the patterned areas were significantly higher than those in the non-patterned and abdominal areas. The expression of the agouti signaling protein 1 (asip1) gene in the abdominal region was significantly higher than in the patterned and non-patterned regions. In the early development of Siniperca chuatsi, the expression of the tyrosinase (tyr) and dct genes began to increase significantly at the gastrula stage (P＜0.05). The tyrp1 gene began to increase significantly at 1 dph (P＜0.05). The expression of the tyr, tyrp1, and dct genes decreased significantly at approximately 7 dph and was maintained at a certain level at 25 dph. In summary, tjp1a, tyr, tyrp1, dct, mitfa, and asip1 help form the body color pattern of Siniperca chuatsi. The expression of tyrp1 lags behind tyr and dct in melanin synthesis during the early development of Siniperca chuatsi. The expression of tyr, tyrp1, and dct tended to be stable after high expression to maintain pattern formation.

Abstract:This study aimed to investigate the metabolic characteristics of hepatocytes under a high-glucose load in spotted sea bass (Lateolabrax maculatus). The liver cell line of L. maculatus was cultured, and two experimental groups were established. The cells from the control group were cultured in a medium containing 5 mmol/L glucose, whereas a medium containing 40 mmol/L glucose was used for the high-glucose group. After 48 h of culture, the cells and supernatants were collected and analyzed. Results showed that the glucose and glycogen contents in the high-glucose group were significantly increased (P＜0.05). The activities of hexokinase (HK), citrate synthase (CS), α-ketoglutarate dehydrogenase (α-KGDHC), isocitrate dehydrogenase (IDH), and succinate dehydrogenase (SDH) increased significantly (P＜0.05). These results indicate that a high-glucose load accelerates glycolysis and the tricarboxylic acid cycle in hepatocytes. In addition, the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the supernatant increased with high-glucose culture (P＜0.05), indicating that high-glucose can cause hepatocyte damage. In the high-glucose group, the ATP content of hepatocytes significantly decreased (P＜0.05). The content of reactive oxygen species (ROS) and MDA was significantly increased (P＜0.05). Furthermore, the high-glucose culture upregulated the expressions of mitochondrial autophagy-related genes (pink, atg5, and mull) and down-regulated the expressions of mitochondrial biogenesis-related genes (nrf-1, pgc-1α, and pgc-1β) (P＜0.05). Sequencing of the mitochondrial genome showed that mitochondrial D-loop genes were mutated under a high-glucose load treatment. In conclusion, in vitro hepatocytes of sea bass showed similar physiological responses to those in vivo when they responded to high-glucose loads. Thus, in vitro hepatocytes could be used as a research platform to study glucose metabolism in fish. High-glucose cultures can lead to increased metabolic enzyme activity in hepatocytes, damaging hepatocytes and mitochondria. This is related to the oxidative stress caused by ROS accumulation. The high-glucose load upregulated the expression of mitochondrial autophagy-related genes and downregulated the expression of mitochondrial generation-related genes, decreasing the number of mitochondria in the cell. Mutations in the mitochondrial D-loop gene occur under a high-glucose load, affecting the structural stability of the mitochondria.

Abstract:This study aimed to investigate the relationship between trypsin and the feeding habits of live prey fish in Siniperca chuatsi and to elucidate the transcriptional regulatory mechanism of the key trypsin gene in S. chuatsi. In this study, we used bioinformatics methods to conduct quantitative, structural, and phylogenetic analyses of trypsin genes in 11 fish species with different feeding habits, combining qPCR, dual-luciferase reporter, and trypsin activity assays to analyze the transcriptional regulation mechanism of the key trypsin gene subtype in S. chuatsi and its correlation with trypsin activity at the first feeding stage. The results showed that a total of 13 trypsin genes distributed at six loci on four chromosomes were identified in S. chuatsi, which was more than that in omnivorous and herbivorous fish, indicating that the amplification of trypsin genes in carnivorous fish is highly adapted to the food environment. Carnivorous S. chuatsi was amplified at key gene loci 2 (SC7-LG17-21898 and SC7-LG17-21899) and 3 (SC7-LG17-21428, SC7-LG17-21429-1, SC7-LG17-21429-2, SC7-LG17-21430-1, and SC7-LG17-21430-2), which are homologous to the key trypsin gene PRSS1 in humans. More significant gene amplification occurred at locus 3, where SC7-LG17-21430-2 had a significantly higher expression level than the other subtypes, indicating that it was the key trypsin subtype in S. chuatsi. The dual-luciferase reporter assay results showed that the promoter activity of three constructed deleted fragments in the 5' flanking region of the SC7-LG17-21430-2 subtype had significant differences, and the region of –593 bp−+20 bp had the highest promoter activity, suggesting it as the core promoter region. Furthermore, PDX1, a transcription factor associated with early pancreatic development, was barely expressed in S. chuatsi at 3 dph and was observed in the core promoter region. Moreover, point mutations in the binding site of PDX1 result in a significant decrease in the promoter activity of the core region. The trypsin activity of S. chuatsi at 3 dph was significantly lower than that of Danio rerio, indicating that the low expression of pdx1 might lead to the low expression of SC7-LG17-21430-2 and low trypsin activity, which could be associated with the unique feeding habits of live prey fish in S. chuatsi. These results provide the groundwork for analyzing the mechanisms underlying the special feeding habits of S. chuatsi.

Abstract:Hippocampus abdominalis are an economically important aquatic species in China. To understand the genetic structure of five populations of the main farmed distended seahorses in China [the third cultured stock in Shangdong province (SD), the first cultured stock in Fujian province (FJ1), the sixth cultured stock in Fujian province (FJ6), the 12th cultured stock in Tai Wan (TW), and breeding offspring of one Australian wild species (AS)], We developed six polymorphic microsatellite markers of the H. abdominalis, and used these 6 microsatellite markers for genetic analysis of five populations of H. abdominalis. The results showed that 63 alleles were detected by 6 pairs of primers in 144 samples. The number of alleles ranged from 8 to 14, with an average of 10.5 and PIC＞0.25, indicating that all 6 microsatellite loci had high polymorphism. In addition, the observed heterozygosity and expected heterozygosity of the five populations were 0.6603 and 0.8104, respectively, indicating that the genetic diversity of the five populations was relatively rich. Further, the molecular variance analysis and genetic analysis was found that the genetic variation of the five populations mainly came from within the population, and a relatively high level of genetic distance was maintained among the 5 populations, among which the genetic distance between Taiwan (TW) and Fujian (FJ1) populations was the largest at 0.4529. In summary, there were genetic differences among the five H. abdominalis populations, and the genetic diversity of the populations was relatively rich and there was no decline in genetic diversity, indicating the 5 H. abdominalis populations could continue to be used for subsequent breeding.

Abstract:To explore the mechanism of intestinal remodeling during the early development of Yangtze sturgeon (Acipenser dabryanus) under artificial breeding conditions, this study applied high-throughput sequencing technology to study the structural characteristics and correlation between the intestinal microbiota and biological feed, Tubificidae, in the early developmental stage of the fish. The results showed that Proteobacteria was the dominant phylum in the intestine of A. dabryanus before feeding, and Proteobacteria and Firmicutes were the main bacteria during the 10th to 40th day of feeding. At the genus level, during the period from not feeding to the 20th day of feeding, the intestinal microbiota was relatively singular, with Pandoraea occupying an absolute dominant position, accounting for more than 88%. On the 30th day of feeding, the intestinal microbiota of A. dabryanus underwent reorganization, with species richness and diversity reaching their peak. The dominant genera became Citrobacter, Lactococcus, Plesiomonas, Staphylococcus, Aeromonas, and Klebsiella. Procrustes analysis showed that, on the 40th day of feeding, the intestinal microbiota of A. dabryanus tended to be consistent with the microbial community composition of the biological feed, Tubificidae, showing a highly significant correlation (P＜0.01). SourceTracker analysis verified that 18.97% of the A. dabryanus intestinal community on the 10th day of open feeding came from the biological feed, Tubificidae. On the 20th day of open feeding, it decreased to 0.15%, and on the 30th day of open feeding, it increased to 51.22%. On the 40th day of open feeding, it reached as high as 97.55%. This study indicated that when feeding A. dabryanus the biological feed, Tubificidae, a turning point in the early developmental stage of the intestinal microbiota occurs on the 30th day of feeding. At this time, the characteristics of the intestinal microbiota changed from high conservatism to good plasticity. Continuing feeding until the 40th day, the intestinal microbiota showed a high consistency with the biological feed microbial community. The results provided a reference for the regulation of intestinal microbiota and healthy cultivation of A. dabryanus in the early development.

Abstract:To investigate potential variances in fish muscle quality under different culture modes and their causes, this study focused on the bighead carp (Hypophthalmichthys nobilis) as a target object. Samples were collected and observed in the Wanghu Lake (Wanghu Lake stocking group) and the surrounding culture ponds (pond culture group) in Hubei Province. The appearance, texture, nutritional value, and flavor characteristics of the back muscles of the two groups of bighead carp were compared. Additionally, the water quality and feed biological composition of the two groups were compared. Results showed that: (1) The intraperitoneal fat (IPF) and hepatopancreas somatic indices (HSI) of bighead carp raised in the Wanghu Lake stocking group were significantly lower than those in the pond culture group (P＜0.05). However, there was no significant difference between the two groups in terms of condition factor (CF) and viscerosomatic index (VSI) (P＞0.05). The luminance value (L^* ) and whiteness value (W) of back skin and meat of bighead carp in the Wanghu Lake stocking group were significantly higher than those in the pond culture group (P＜0.05). (2) The elasticity and cohesion of the bighead carp muscles in the Wanghu Lake stocking group were higher than those in the pond culture group (P＞0.05), whereas hardness was significantly lower than that in the pond culture group (P＜0.05). (3) The water and crude protein content of bighead carps in the Wanghu Lake stocking group were significantly lower than those in the pond culture group (P＜0.05). The crude fat content was significantly higher than that in the pond culture group (P＜0.05). The essential amino acid content and score of bighead carp in the Wanghu Lake stocking group were significantly higher than those in the pond culture group (P＜0.05). The essential amino acid (EAA)/toal amino acid (TAA) values of the Wanghu Lake stocking and pond culture groups were 41.24% and 40.84%, the ratio of EAA/nonessential amino acid (NEAA) was 84.18% and 83.03%, respectively, meeting the FAO/WHO ideal model standards. However, the levels of monounsaturated and polyunsaturated fatty acids in the Wanghu Lake stocking group were significantly higher than those in the pond culture group (P＜0.05). The concentrations of Ca and Zn in the muscles of bighead carp in the Wanghu Lake stocking group were higher than those in the pond culture group (P＞0.05). (4) The proportion of fresh amino acids was higher and the proportion of bitter amino acids was lower in the Wanghu Lake stocking group. The highest odor activity values were observed for the grassy odor hexanal and fatty odor 1-octanal in the Wanghu Lake stocking and pond culture groups, respectively. Additionally, the content of volatile compounds such as 1-hexanol and 3-pentanone in the Wanghu Lake stocking group was lower than that in the pond culture group, and the relative odor activity value (ROAV) of these volatile compounds in the pond culture group was lower than that in the pond culture group. The results showed that bighead carp reared in the Wanghu Lake stocking group had better morphological characteristics, muscle nutrition, and flavor quality than those reared in the pond culture group, associated with differences between the culture environment and natural bait. The conclusions of this study provide a theoretical reference for the development of large-scale ecological fisheries.

Abstract:During the fishing and transportation processes of farmed fish, they are stimulated by various stressors, such as high density, hypoxia, vibration, and sound, which can damage the fish body or cause rapid death. Carboxylic acid (CA) is an important edible organic acid that is easily soluble in water, inexpensive, and readily available. CA is often added as a feed additive in formula feed to improve the growth performance of farmed fish, maintain intestinal health, and enhance immune and stress resistance. However, there have been few reports on the use of CA in water to enhance the ability of fish to resist acute stress. Largemouth bass (Micropterus salmoides) is a widely cultivated and economically important fish in China; however, it is not tolerant of low oxygen levels. Largemouth bass will surface and die when dissolved oxygen (DO) is below 2 mg/L. Deaths caused by acute hypoxic stress during fishing and transportation have attracted considerable attention. To investigate the effects of CA added to water on the hypoxia tolerance of largemouth bass under acute hypoxia stress, using juvenile largemouth bass [mean weight: (18.53±0.43) g] as the study subject, CA was added to the culture water to a final concentration of 0 (T0), 0.01‰ (T1), 0.05‰ (T2), and 0.10‰ (T3), respectively, and oxygenation was stopped in the water with an initial dissolved oxygen concentration of 7.5 mg/L. Acute hypoxic stress was applied for 2.5 h, and the DO in the water was measured every 0.5 h. The DO concentration in the control group was (7.5±0.2) mg/L. At the end of the stress period, stress tolerance, body damage, and mortality were assessed. The results showed that, compared with the T0 group, the oxygen consumption of the T2 group during the first 2.5 h of acute hypoxic stress significantly decreased. The T3 group had significantly reduced oxygen consumption and mortality rates of largemouth bass under acute hypoxic stress (P＜0.05). Compared with the control group, the stress-related indicators of cortisol (COR), lactate (LD), and glucose (GLU) in the plasma of largemouth bass in the T0 group were significantly increased, and the levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), which characterize oxidative damage in the body, were significantly increased. The activities of glutamic oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT), which characterize liver damage, were significantly increased (P＜0.05). Compared with the T0 group, there were no significant differences in various indicators in the plasma of the T1 group of largemouth bass (P＞0.05). The hemoglobin (Hb) content in the blood of the T2 group significantly increased, while the LD content and GOT and GPT activities in the plasma significantly decreased (P＜0.05). The number of red blood cells (RBC) and Hb content in the blood of the T3 group significantly increased, while the levels of COR, LD, and H₂O₂ in plasma significantly reduced, and the activities of GOT and GPT significantly decreased (P＜0.05). Compared to the control group, the transcription levels of the cysteine proteolytic enzyme 3 (caspase-3) and cysteine proteolytic enzyme 8 (caspase-8) genes related to liver apoptosis in the T0 group of largemouth bass were significantly higher (P＜0.05). Compared with the T0 group, the transcription level of the caspase-3 gene in the liver of the T1 group significantly decreased (P＜0.05). The transcription level of the glucose transporter-1 (glut-1) gene in the liver of the T2 group of largemouth bass significantly increased, while the transcription level of the caspase-3 gene significantly decreased (P＜0.05). The transcription level of hypoxia-inducible factor 1 (hif-1α) and glut-1 gene in the liver of the T3 group significantly increased, while the transcription level of the caspase-3 gene was significantly reduced (P＜0.05). In summary, acute hypoxic stress caused oxidative stress, body damage, and even mass mortality in largemouth bass; 0.10‰ CA could improve the ability of largemouth bass to resist acute hypoxic stress, alleviate the damage caused by acute hypoxic stress on the body, and reduce mortality. This study provides the data and a reference for solving the problem of acute hypoxic stress in fish during fishing and transportation.

Abstract:To study the interactive effects of different zinc sources and levels with vitamin D₃ on the growth performance, carcass trace element content, and antioxidant capacity of grass carp (Ctenopharyngodon idella), 600 grass carp with a body mass of (25.86±0.13) g were selected. The experiment consisted of eight treatments (three replicates per treatment, 25 fish per tank). Fish were randomly placed in 24 tanks with a volume of 900 L each. In this study, two factors and two levels of dietary vitamin D₃ (1000 and 2000 IU/kg), together with three levels of dietary zinc methionine (0, 25, and 50 mg/kg), were designed. Treatment with 25 mg/kg zinc sulfate heptahydrate at two levels of dietary vitamin D₃. Eight isonitrogenous and isolipidic diets were used in the 8-week growth trial. The eight treatment groups were named 1000D/Zn0 (1000 IU/kgVD₃+0 mg/kg zinc), 1000D/ZnS25 (1000 IU/kgVD₃+25 mg/kg zinc sulfate heptahydrate), 1000D/ZnM25 (1000 IU/kgVD₃+25 mg/kg zinc methionine), 1000D/ZnM50 (1000 IU/kgVD₃+50 mg/kg zinc methionine), 2000D/Zn0 (2000 IU/kgVD₃+0 mg/kg zinc), 2000D/ZnS25 (2000 IU/kgVD₃+25 mg/kg zinc sulfate heptahydrate), 2000D/ZnM25 (2000 IU/kgVD₃+25 mg/kg zinc methionine), and 2000D/ZnM50 (2000 IU/kgVD₃+50 mg/kg zinc methionine), respectively. Results showed that: (1) Dietary zinc levels and vitamin D₃ had significant interaction effects on the weight gain rate (WG), feed conversion ratio (FCR), and protein efficiency ratio (PER) of grass carp (P＜0.05). The 1000D/ZnM50 group exhibited the lowest FCR and the highest PER. Compared to the 1000D/ZnS25 group, the 1000D/ZnM25 group showed a significant decrease in FCR and a significant increase in PER (P＜0.05). The WG of the 2000D/ZnM25 group was significantly increased (P＜0.05). The PER of the 2000D/ZnM25 group was significantly higher than that of the 2000D/ZnS25 group, and the FCR was significantly lower than that of the 2000D/ZnS25 group (P＜0.05). (2) No interactive effects exist between dietary zinc and vitamin D₃ on copper, iron, manganese, zinc, and calcium in the carcasses of grass carp (P＞0.05). The iron and calcium contents of grass carp carcasses in the 2000 IU/kg vitamin D₃ group were significantly higher than those in the 1000 IU/kg vitamin D₃ group. The iron content of grass carp carcasses in the ZnM25 and ZnM50 groups was significantly higher than in the Zn0 group. The zinc content increased with the increase in methionine zinc levels. The manganese content of grass carp carcasses in the ZnM50 group was significantly lower than that in the Zn0 and ZnM25 groups (P＜0.05). (3) Interactive effects exist between dietary zinc levels and vitamin D₃ on the activities of catalase(CAT), superoxide dismutase(SOD), AKP(alkaline phosphatase) and LZM(lysozyme) in the liver of grass carp. The interaction between zinc sources and vitamin D₃ significantly affected LZM (P＜0.05). The activities of CAT, SOD, AKP, and LZM in the livers of grass carp in the 2000D/ZnM25 group were significantly higher than those in the other groups, except for the 2000D/ZnM50 group, in which the MDA content was significantly reduced. Compared with the 2000D/ZnS25 group, the activities of CAT, AKP and LZM in the 2000D/ZnM25 group were significantly higher (P＜0.05). These results indicated that the interactive effects of zinc and vitamin D₃ in grass carp feed could significantly improve the growth performance and antioxidant capacity of grass carp. Under the conditions of this experiment, zinc methionine (25 mg/kg) and vitamin D₃ (2000 IU/kg) were more conducive to the growth and antioxidant capacity of grass carp, and zinc methionine was superior to zinc sulfate in terms of growth, feed utilization, carcass trace element content, and antioxidant capacity.

Abstract:This study aims to analyze the differences in acoustic density of fishery resources between surface and bottom layers (surface mixed layer and bottom cold water layer) in the northern South China Sea and to explore the relationship between these differences and 41 abiotic factors. This research provides a scientific basis for the effective management and conservation of fishery resources in the northern South China Sea. The northern offshore area of the South China Sea is a crucial traditional fishing ground and an important spawning and feeding ground for marine fish. In recent years, fishery resources in this region have shown significant declines in age, size, and quality, attracting significant attention from both academia and fishery management authorities. Fishery acoustic methods were employed, using a Simrad EY60 split-beam scientific echosounder to collect acoustic data in the northern South China Sea. Acoustic data were analyzed using the Echoview fishery acoustic data processing system to calculate the acoustic density (NASC) of surface and bottom layers. Extreme Gradient Boosting (XGBoost) and Random Forest algorithms were utilized to model the influence of 41 abiotic factors on the differences in acoustic density and to assess the importance of these factors. Results indicated that the bottom layer had significantly higher acoustic density than the surface layer, with mean values of 106.00 m²/nmi² and 43.39 m²/nmi², respectively. Both XGBoost and Random Forest models performed similarly, with temperature factors (bottom 2 m temperature, surface-bottom temperature difference, and surface 2 m temperature) and water depth identified as the most critical factors affecting acoustic density differences. The negative value region, where surface density exceeds bottom density, is primarily distributed around Hainan Island. The study concluded that temperature and water depth are the primary factors influencing the distribution differences of fishery resources, while human activities may also contribute by altering the concentrations of factors such as phosphate and chlorophyll. Additionally, the discussion highlights the implications of these findings for fisheries management, suggesting that targeted measures to monitor and regulate temperature and nutrient levels could significantly improve resource sustainability. The analysis underscores the importance of incorporating advanced machine learning algorithms in marine resource assessment to enhance the accuracy and reliability of environmental impact evaluations. These findings provide vital scientific insights for the management and conservation of fishery resources in the northern South China Sea, offering a comprehensive understanding of the environmental factors that drive spatial distribution patterns in marine ecosystems. This research thus lays a foundation for future studies aiming to mitigate the impacts of climate change and human activities on marine biodiversity and resource availability.

Abstract:The Heilongjiang River is located in a high-latitude cold region, and the natural Reproduction and early-stage resource occurrence of fish have their own uniqueness. Understanding the spatial patterns of drifting fish eggs species and community structure is of great significance for the conservation of Heilongjiang River fish resources. From June to July 2022, a monitoring study of drifting fish eggs was conducted in three river sections of the Heilongjiang River main streams: Fuyuan, Qindeli, and Luobei. DNA barcoding technology was used to identify the species of fish eggs, resulting in the acquisition of 1179 CO I gene sequences, identifying a total of 15 fish species belonging to 2 orders, 3 families, 8 subfamilies, and 15 genera. Among them, the Cyprinidae family was the most represented with 13 species, accounting for 83.29%, followed by one species each in the Cobitidae and Sinipercidae families, accounting for 16.45% and 0.25% respectively. The analysis results showed that the species composition of drifting fish eggs was mainly composed of small fish such as Hemiculter bleekeri, Parabotia fasciatus, and Gobiobotia pappenheimi. Community diversity was highest in the Fuyuan section and showed a decreasing trend upstream, demonstrating clear spatial heterogeneity. The relative importance index (IRI) of important economic fish species such as Hypophthalmichthys molitrix, Ctenopharyngodon idella, Elopichthys bambusa, Culter alburnus, Parabramis pekinensis, and Siniperca chuatsi shows a significant decreasing trend from Fuyuan (downstream) to Luobei (upstream), implying that the spawning stock in the Fuyuan section is larger than in the upstream sections, while the resources in the Luobei section are facing decline. This study suggests that environmental factors and overfishing are likely the main factors affecting the early resources of important economic fish species. It is recommended to establish fishing bans and closed seasons in spawning grounds, reduce fishing intensity, and conduct long-term monitoring studies of early resources such as fish eggs and larvae to scientifically protect and rationally utilize Heilongjiang River fishery resources.