Fish Physiology and Biochemistry最新文献

Aquaculture is a crucial sector in the global food system, significantly contributing to the supply of nutritious food and creating economic opportunities. This review article examines the essential role of vitamins in fish farming, highlighting their contributions to growth performance, immune function, antioxidant activity, digestive efficiency, disease resistance, and overall body composition. Vitamins are not only vital nutrients for the growth and metabolic functions of aquatic organisms but also serve as essential cofactors in numerous biochemical reactions, thereby promoting fish health and development. Recent innovations in aquafeed formulations and vitamin nutrition have led to a reassessment of the dietary vitamin needs for various farmed fish species. This review synthesizes contemporary research in fish nutrition, demonstrating the substantial effects of vitamins on growth rates (up to 20%), immune response enhancement (up to 40%), optimization of digestive and hepatic enzyme activities, and improvement of biochemical and hematological parameters. The magnitude of these benefits is influenced by factors such as vitamin type, fish species, age, and environmental conditions. Additionally, the review highlights the significance of vitamins in enhancing disease resistance and improving body composition in aquaculture species. The insights provided aim to guide aquaculture professionals and researchers in recognizing the critical role of vitamins in fostering sustainable fish farming practices. Future research in fish nutrition should prioritize the development of sustainable vitamin supplementation strategies, including the exploration of plant-based and microbial vitamin sources, the optimization of nutrient delivery methods, and the reduction of environmental impacts. By focusing on these areas, we can enhance fish health, improve feed efficiency, and promote more environmentally sustainable aquaculture practices.

The olive flounder (Paralichthys olivaceus) is an economically important species in South Korea. However, the specific dietary requirement for tryptophan (Trp) has not been determined for this species at any growth stage. Thus, this study aimed to determine the dietary Trp requirement for juvenile olive flounder under low water temperature conditions. Two consecutive feeding trials were conducted, each using diets with different concentrations of dietary Trp: Exp-Ⅰ (0.39-14.46 g kg^-1) and Exp-Ⅱ (0.93-6.96 g kg^-1). The initial mean body weights of the olive flounder were 4.38 ± 0.03 g (Exp-Ⅰ) and 18.4 ± 0.1 g (Exp-Ⅱ). In Exp-Ⅰ and Exp-Ⅱ, fish were randomly distributed into 18 tanks (120 L), corresponding to six dietary groups with three replicates per group (30 fish per tank). Fish were fed the experimental diets for 13 weeks (Exp-Ⅰ) and 8 weeks (Exp-Ⅱ). The water temperatures during the trials were 18.2 ± 2.4 ℃ in Exp-Ⅰ and 17.5 ± 2.8 ℃ in Exp-Ⅱ, representing suboptimal thermal conditions. The results indicate dietary Trp concentration significantly affected the growth and survival of the fish. In particular, the lowest growth and survival were observed in fish fed the diet with the lowest concentration of Trp in both feeding trials. Additionally, the fish fed the Trp-deficient diet (0.39 g kg^-1) exhibited lower levels of hematological parameters, immunity, antioxidant capacity and whole-body crude protein compared to Trp supplemented groups (2.33-14.46 g kg^-1). In fish fed a Trp-deficient diet (0.39 g kg^-1), expression of tight junction proteins was down-regulated, abnormal development of mucosal folds was observed, and intestinal inflammatory cytokines were upregulated compared to Trp supplemented groups (2.33-14.46 g kg^-1). Fish fed Trp-supplemented diets showed significantly higher plasma levels of Trp, serotonin, melatonin and cortisol compared to those fed the Trp-deficient diet. The dietary Trp concentration required for fish growth was estimated to be 3.08 g kg^-1 (6.06 g kg^-1 of protein) in the juvenile stage (Exp-Ⅰ) and 2.17 g kg^-1 (4.27 g kg^-1 of protein) in the post-juvenile stage (Exp-Ⅱ), respectively, as determined by broken-line regression based on final body weight.

4-Methylimidazole (4-MEI) is a widely used industrial compound and a common byproduct of caramelization in various foods and beverages. It enters aquatic ecosystems through multiple ways and is a well-recognized toxic and potentially carcinogenic substance in humans. In this study, the median lethal concentration (LC₅₀) of 4-MEI for Ctenopharyngodon idella over 96 h was determined for the first time in fish and found to be 26.79 mg/L. Subsequently, to assess its toxicological impact, C. idella fingerlings were exposed to an acute concentration (LC₅₀ for 96 h) and two sublethal concentrations, 1/5th (5.35 mg/L) and 1/10th (2.69 mg/L) of the LC₅₀, over 35 days. Acute exposure resulted in significant adverse effects, including substantial increases in white blood cell count, total immunoglobulins, lysozyme activity, phagocytic activity, respiratory burst, and the enzymatic activities of AST, ALT, ALP, and LDH. There was also upregulation of key immune-related genes: TNF-α, Interleukin-1β, Lysozyme-C, and Lysozyme-G. In contrast, red blood cell count, hemoglobin levels, hematocrit, total protein, albumin, globulin, and the albumin-to-globulin ratio were significantly reduced. Sublethal exposures produced concentration-dependent toxic effects. Histological analysis revealed that fish exposed to acute concentration exhibited marked structural alterations (> 50%) in liver and gill tissues. However, the sublethal concentration exposure (1/5th and 1/10th of LC₅₀) induced moderate (< 50%) to mild (< 10%) histopathological changes, respectively. These findings demonstrate the toxic effects of 4-MEI on fish and highlight the urgent need for increased awareness regarding its environmental risks and impact on aquatic life.

Heat shock proteins (HSPs) are molecular chaperones that play a crucial role in fish physiology from stress-induced damage by stabilizing proteins and enhancing survival under environmental challenges. This study characterizes the stress-responsive hsp70 (tb-ihsp70) gene in Trachinotus blochii, a prime marine aquaculture species, from an evolutionary perspective and links its expression to salinity and pathogen stress. The tb-ihsp70 encodes a 639 amino acid protein with conserved ATPase and substrate-binding domains critical for protein conformation under stress. Phylogenetic analysis grouped it within Carangidae, showing a strong link to Trachinotus ovatus, with marine and freshwater species forming distinct clades, reflecting the environmental role in its phylogeny. Structural modelling revealed a Y-shaped conformation with high-confidence validation scores. STRING analysis identified functional partners, highlighting involvement in broader stress response pathways. The intronless feature and expression profiling classified tb-ihsp70 as a constitutively expressed and moderately inducible HSP70. Expression in healthy fish was maximum in gill > posterior kidney > spleen > liver > heart. Salinity stress showed significant upregulation at 3‰ on day two (7.95-fold) and three (5.26-fold), while no significant changes were observed at 42‰ on any day, indicating a stronger and longer tb-ihsp70 induction at lower salinity levels. Vibrio harveyi challenge peaked expression at 12 h in spleen (73.86-fold), heart (40.88-fold), and posterior kidney (23.10-fold). In conclusion, this first comprehensive characterization underscores the role of tb-ihsp70 in biotic and abiotic stress adaptation, supporting its potential as a molecular biomarker for T. blochii health research in mariculture.

Digestion is primarily performed by digestive enzymes. Here, we examined the activity levels of seven digestive enzymes along the digestive tract of the herbivorous fish, Cebidichthys violaceus. We reared C. violaceus on carnivore, omnivore, and herbivore diets in the laboratory for nine months and compared the digestive enzyme activities among the fish on the different diets and with wild-caught fish consuming their natural foods. Enzymatic activities were generally lower in the laboratory than in wild-caught fish. The marked anterior-to-posterior amylase activity gradient along the gut in wild-caught fish was absent in the lab-fed fish. We hypothesize that the dampened enzymatic activity may have been caused by reduced food intake in the laboratory in comparison to the wild fish. N-acetyl-β-D-glucosaminidase (NAGase) activity (degrades chitin breakdown products) peaked in the distal intestines of the lab-fed fish, but not the wild fish. The role of this enzyme in the digestive process remains unknown since the lab diets contained no chitin, and its origin may have been microbial. Overall, C. violaceus can tolerate diets with a wide range of protein and carbohydrate levels. However, the totality of our data suggests that live algal diets may be best for this herbivorous fish in a captive setting, especially for aquaculture.

Gill function in gas exchange and ion regulation is crucial for ionoregulatory homeostasis in teleost fishes, yet further research is needed to elucidate how cold stress affects these processes, particularly in relation to salinity-dependent tolerability. Indian medaka (Oryzias melastigma) were acclimated to freshwater (FW) and seawater (SW) environments before being exposed to cold stress at 18 °C for 168 h. The protein abundance of the apoptotic marker Caspase-3 increased significantly in SW-acclimated fish compared to controls, indicating a heightened apoptotic response under cold stress in SW conditions. Concurrently, the expression of the anti-apoptotic gene birc5 exhibited distinct patterns in FW and SW, suggesting differential regulatory mechanisms in response to cold exposure. Transcriptomic analysis revealed that cold stress significantly influenced genes related to ion regulation, osmoregulation, and cellular metabolism, with distinct pathways activated in FW and SW environments. Notably, SW-specific genes were predominantly involved in metabolic pathways and stress signaling, while FW-specific genes were linked to transport processes and cellular maintenance. Additionally, cold stress significantly affected the expression of Na⁺/K⁺-ATPase (NKA) subunits and ion transport genes, underscoring the impact of temperature and salinity on gill function. The study highlights the importance of tight junctions (TJ) and gap junction (GJ) in maintaining gill integrity during environmental stress, with differential regulation of key genes like ocln, cask, and gja3 in response to salinity and temperature shifts. These findings highlight the superior molecular and cellular adaptations of euryhaline fish in SW to cold stress, emphasizing how salinity enhances gill responses and suggesting potential strategies for improving cold tolerance in aquaculture.

Rainbow trout (Oncorhynchus mykiss), which is rich in high-quality protein and polyunsaturated fatty acids (PUFAs), is one of the most commercially important aquaculture species worldwide. The fatty acid profiles of trout, however, might be substantially influenced by different stocking densities. The present study aims to evaluate the effects of stocking density on the fatty acid composition and hepatic metabolomics of rainbow trout. Juvenile rainbow trout were reared for 84 days in circular tanks at 3 distinct levels of stocking density, i.e., low (group LD, 9.15 g/L), moderate (group MD, 13.65 g/L), and high (group HD, 27.31 g/L). The results showed that the levels of C22:6 n-3 (Docosahexaenoic acid, DHA) and total n-3 PUFAs in the dorsal muscles of the fish at group MD were significantly higher than those at groups LD and HD (p < 0.05). For ventral muscles, fish at group HD showed significantly decreased content of C16:1n-9 (palmitoleic acid) and n-3 PUFAs compared to those at groups LD and MD (p < 0.05). Hepatic fatty acid profiles showed significant reductions in monounsaturated fatty acids (MUFAs) for the fish at groups MD and HD compared to those at group LD (p < 0.05). Moreover, the concentrations of total n-6 PUFAs in the dorsal muscle were positively correlated with stocking density (R = 0.7357, p = 0.0238), while the levels of total n-3 PUFAs in the ventral muscle (R =  - 0.8478, p = 0.0039) and the levels of total MUFAs in the liver (R =  - 0.7837, p = 0.0101) showed negative correlations to the fish stocking densities. Metabolomics analyses further revealed that stocking density influenced the pathways related to glycerophospholipid metabolism, fatty acid degradation, and arachidonic acid metabolism. The results suggested that high stocking density altered fatty acid profiles and enhanced antioxidant and inflammatory responses in rainbow trout, providing valuable insights for optimizing aquaculture practices to improve the nutritional quality of farmed trout.

With the rise of long-distance transport in aquaculture, temperature has become a key factor affecting juvenile fish survival and health. However, their molecular adaptation to transport temperature is not well understood. In this study, physiological and transcriptomic analyses were conducted to investigate the effects of transport temperatures on juvenile Siniperca chuatsi. With 25 °C non-transported fish as the control (C25), three transport temperature groups were established: transport at 15 °C (T15), transport at 25 °C (T25) and transport at 30 °C (T30). Comparative analyses were then performed between each transport group and the control (T15 vs. C25, T25 vs. C25 and T30 vs. C25). Liver damage became progressively more severe with increasing transport temperature, reaching its peak at T30 with pronounced edema and necrosis. Transcriptomic analysis identified over 5463 DEGs and three WGCNA modules significantly associated with temperature variation. Hub genes in the MEdarkseagreen4 module (T30) were enriched in lysosomal activity, calcium signaling and cytoskeletal regulation, indicating disrupted cellular homeostasis as a key driver of liver damage. At T15, the MEcyan module was enriched with upregulated hub genes for ribosome function and fatty acid metabolism, indicating boosted protein synthesis and energy use under low-temperature transport. In the T25, hub genes in the MEpalevioletred3 WGCNA module showed downregulation of oxidative phosphorylation and insulin signaling pathways, indicating a suppression of energy metabolism and growth signaling as part of a stress-adaptive strategy. These results deepen our understanding of the molecular mechanisms underlying temperature adaptation in eurythermal fish during simulated transport.

Spotted seabass (Lateolabrax maculatus) is an economically important fish species in China. In this study, the muscle of L. maculatus was used as a material, and the muscle cell line was successfully established using the tissue block method. The established muscle cell line exhibited vigorous growth and had been successfully passaged for more than 100 generations, maintaining stable polygonal cell morphology. The cell viability of L. maculatus muscle cell line exhibited a notable increase following a 24-h treatment with 30 $\mu$ M taurine, and the relative expression of myogenic regulatory factors myf5 and myf6 was significantly increased. Therefore, the muscle cell line of L. maculatus was successfully established and served as a valuable resource for conducting fundamental research in L. maculatus, providing essential materials for gene function analysis, cytogenetics, and nutritional metabolism mechanism in L. maculatus.

Overripening of ovulated oocytes, often resulting from spawning delays in aquaculture, is triggered by apoptosis and significantly compromises early fertilization in fish. Targeting apoptosis pathways offers a promising approach to enhance reproductive outcomes, particularly given the controversial role of melatonin in apoptosis regulation, this study assessed the impact of oral melatonin supplementation at doses of 0, 50, and 200 mg/kg of dry feed on the expression of key apoptosis-related genes (Bcl-2, p53, caspase-9) and fertilization percentages in rainbow trout (Oncorhynchus mykiss) oocytes at two post-ovulation time points: immediately post-ovulation (day 0) and after 7 days of post-ovulatory ageing (overripening). Gene expression was quantified using real-time PCR, and fertilization percentages were evaluated to determine reproductive outcomes. Melatonin treatment notably upregulated the anti-apoptotic gene Bcl-2 and downregulated the pro-apoptotic genes p53 and caspase-9. While no significant differences were detected between the 50 and 200 mg doses for p53 and caspase-9 expression, the 200 mg dose demonstrated a more pronounced effect on improving fertilization percentages in overripened oocytes. In contrast, fertilization percentages declined sharply in the control group during overripening. Both melatonin dosages significantly improved fertilization percentages compared to the control, with higher doses showing greater effectiveness. These results suggest that melatonin alleviates the detrimental effects of oocyte overripening by modulating apoptosis pathways and enhancing fertilization outcomes. Melatonin supplementation may be a practical approach in aquaculture to extend oocyte viability and improve reproductive performance in delayed spawning scenarios.