This study evaluated the comprehensive effects of dietary taurine supplementation in low-fishmeal (FM) diets on physiological functions of Japanese seabass (Lateolabrax japonicus). A 3 × 3 factorial design was employed in this study. Three FM levels were set as 25% (FM25, basal level), 20% (FM20), and 15% (FM15), where soybean meal and soy protein concentrate were used to replace 20% and 40% of FM protein, respectively. Each FM group was further supplemented with 0%, 0.5%, or 1.0% taurine. A total of 540 juvenile fish with an initial body weight of 6.95 ± 0.18 g were randomly divided into 27 tanks (3 tanks per group, per tank 20 fish) and fed the experimental diets for 8 weeks. The results demonstrated that weight gain rate and specific growth rate were significantly influenced by both FM level and taurine level (P < 0.05). The FM20 group supplemented with 1.0% taurine showed optimal growth performance. Taurine supplementation significantly enhanced antioxidant capacity across multiple tissues, as evidenced by increased glutathione (GSH) content in serum (P = 0.028), liver (P < 0.001) and muscle (P < 0.001), along with reduced malondialdehyde (MDA) levels in intestine (P < 0.001), liver (P < 0.001), and muscle (P < 0.001). In terms of immunoregulation, taurine significantly improved non-specific immunity, indicated by elevated acid phosphatase (ACP) activity (P <0.001), albumin (ALB) content (P < 0.001), as well as reduced alanine aminotransferase (ALT) (P < 0.001) and aspartate aminotransferase (AST) (P < 0.001) activities in serum, though responses varied with FM levels. Histological analysis revealed that taurine alleviated hepatocyte vacuolation induced by replacing FM with plant-based protein. Additionally, 1.0% taurine addition significantly increased intestinal muscularis thickness and villus height (P < 0.05) and alleviated the increase relative mRNA expression of inflammatory cytokines (il1β, il2, il4, and il8) (P < 0.05) and apoptotic factors (caspase 3, 8, and 9) (P < 0.05) caused by FM substitution. Increased myofiber frequency and upregulation relative mRNA expression levels of mtor and s6k1 (P < 0.05) suggested that taurine supplementation enhanced muscle protein synthesis. In conclusion, taurine exerts multiple beneficial effects in low-FM diets for Japanese seabass, providing important theoretical and practical insights for developing sustainable aquafeeds and promoting aquaculture development.

Phosphatidylcholine (PC) is critical for aquatic feed, but the physiological functions of marine-derived PC remain unclear. This study explored the regulatory role of Atlantic herring (Clupea harengus) egg-derived DHA-enriched PC (DHA-PC) in healthy farming of largemouth bass. An 8-week trial was conducted on juvenile largemouth bass (initial body weight: 4.31 ± 0.038 g) with 0% (control group), 3% and 6% DHA-PC supplementation. Results showed that DHA-PC enhanced serum immune indicators (alkline phosphatase (AKP) activity and albumin (ALB) content) and reduced alanine aminotransferase (ALT) activity, while improving antioxidant capacity (increased reduced glutathione (GSH) content, superoxide dismutase (SOD) activity, total antioxidant capacity (T-AOC) activity and decreased malondialdehyde (MDA) content) in multiple tissues. A total of 496 and 673 differentially expressed genes (DEGs) were identified in muscle transcriptomics between the CON group and the MDHAPC group, and between the CON group and the HDHAPC group, respectively, with enriched apoptosis-related mitogen-activated protein kinase/forkhead box O transcription factor (MAPK/FOXO) pathways. Quantitative real-time polymerase chain reaction (qRT-PCR) confirmed downregulated apoptosis genes (nfat2, jund, ap1, etc.) by DHA-PC. DHA-PC increased the activity of lipase and increased the mRNA expression of lpl and atgl in the intestine. In addition, DHA-PC optimized intestinal structure, upregulated tight junction/antioxidant genes (zo-1, claudin-1, cat and nrf2), downregulated inflammatory genes (il-1β and tlr2), and modulated intestinal flora (increased beneficial bacteria and reduced pathogens). In conclusion, dietary DHA-PC improves muscle and intestinal health via the "intestinal-muscle axis", providing a theoretical basis for its application as a novel nutritional strategy in aquaculture. Moreover, comparative analysis revealed that 3% DHA-PC supplementation was sufficient to achieve significant antioxidant effects, whereas 6% DHA-PC was more effective in optimizing intestinal microbial community structure.

This study applied synthetic biology principles to engineer Saccharomyces cerevisiae with a heterologous astaxanthin pathway, creating a high-yield strain. Fermenting soybean meal (SBM) with this strain produced astaxanthin-enriched fermented SBM (AFSBM; 43.8 mg/kg astaxanthin) while significantly reducing antinutritional factors (e.g., oligosaccharides, urease). AFSBM's potential in largemouth bass (Micropterus salmoides) feed was evaluated using five isonitrogenous (48% crude protein) and isolipidic (10% crude fat) diets where AFSBM replaced 0%, 15%, 30%, 45%, or 60% of fish meal (FM) protein (basal diet: 40% FM). After an 8-week feeding trial (initial weight: 8.70±0.03 g), AFSBM replacement ≤30% did not inhibit growth performance (weight gain rate, specific growth rate), but levels ≥45% caused significant inhibition. Higher replacement upregulated intestinal amino acid transporter (slc7a5, slc7a8) mRNA expression. Replacing 30% FM protein with AFSBM significantly enhanced tissue antioxidant capacity, increased intestinal villus height, and improved muscle texture (TPA analysis). AFSBM substitution also reshaped gut microbiota homeostasis, reduced microbial diversity at higher levels, and enriched differential taxa in amino acid metabolism pathways (e.g., glycine, serine, threonine). In a 40% FM basal diet, replacing 30% FM protein with AFSBM enhances antioxidant status, improves intestinal morphology and muscle quality in largemouth bass without compromising growth. This demonstrates synthetic biology's potential for developing high-value, upgraded plant-based feed ingredients.

This study evaluated the influence of dietary reuterin on the growth performance, antioxidant capacity, and immune metabolism of largemouth bass (Micropterus salmoides), with a further objective of unraveling the key molecular pathways responsible for these physiological alterations. A seven-week feeding trial was conducted on largemouth bass (initial weight 3.07 +/- 0.02 g) to assess the effects of dietary reuterin. The fish were reared on one of six isonitrogenous and isolipidic diets containing incremental levels of reuterin (0, 0.01, 0.02, 0.04, 0.08, and 0.16 g/kg), which ultimately led to significant enhancements in both weight gain rate (WGR) and specific growth rate (SGR). Based on a quadratic regression analysis of WGR and SGR, the optimal dietary supplementation level of reuterin was determined to be 0.09 g/kg. Fish fed reuterin exhibited enhanced liver antioxidant capacity, evidenced by increased activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and catalase (CAT), and a significant reduction in malondialdehyde (MDA) content. At the transcriptional level, reuterin supplementation actively promoted the expression of genes associated with antioxidant defense and glutathione synthesis, such as nrf2, sod1, cat, gpx, gss, and gst. Conversely, it suppressed the transcription of key pro-inflammatory cytokines (tnf-alpha, il-1 beta, il-8) and mediators of apoptosis (casp8, casp9, bax). A combined investigation of the liver transcriptome and metabolome revealed that reuterin substantially alters pivotal metabolic pathways. The primary routes affected by this remodeling included the metabolism of glutathione, arginine and proline, and arachidonic acid. These changes suggest that reuterin enhances the antioxidant defense system, at least in part, by activating the nrf2 signaling pathway and promoting the glutathione metabolic cycle, which in turn mitigates inflammatory responses. In conclusion, dietary reuterin supplementation can effectively promote growth and enhance the antioxidant and immune functions of largemouth bass, highlighting its potential as a beneficial feed additive in aquaculture.

Under global warming, thermal stress has emerged as a significant environmental threat to the sustainable aquaculture of largemouth bass. This study systematically investigated the mechanisms by which dietary astaxanthin alleviates intestinal oxidative stress, inflammatory responses, and metabolic remodeling in largemouth bass (Micropterus salmoides) under acute thermal stress. Fish were fed either a basal diet (0 mg/kg astaxanthin) or an astaxanthin-supplemented diet (150 mg/kg) for eight weeks, followed by exposure to 35 °C (at a heating rate of 1 °C/h). Transcriptomic analysis revealed that heat stress markedly activated immune pathways (NF-κB, TLR, apoptosis) and disrupted glutathione, arachidonic acid, glycerophospholipid, and arginine and proline metabolism pathway. Metabolomic profiling further confirmed significant alterations in lipid and amino acid metabolism, characterized by the accumulation of pro-inflammatory lipid mediators (Leukotriene D4, Prostaglandin E2) and depletion of glutathione. Integrated multi-omics and quantitative validation demonstrated that astaxanthin supplementation upregulated key antioxidant and synthesis genes (e.g., gclc, gclm, GST, GPX, GGT), promoted glutathione synthesis, and suppressed NF-κB activation, thereby alleviating oxidative stress and inflammatory injury. In addition, astaxanthin facilitated glycerophospholipid remodeling, enhancing de novo phospholipid synthesis and reacylation, which improved intestinal mucosal stability and supported barrier repair. Gene expression validation further showed that inflammatory cytokines (tnfα, il8) and apoptosis-related genes (casp8, bax) were significantly downregulated at critical time points (8-12 h) in the astaxanthin group (P < 0.05), confirming its inhibitory effects on inflammatory and apoptotic cascades. Overall, dietary astaxanthin exerts dual protective roles by strengthening antioxidant defenses and suppressing inflammation, while simultaneously promoting intestinal barrier repair. These findings provide theoretical support for the application of astaxanthin as a functional feed additive in aquaculture.

Biofloc technology (BFT) is an advanced aquaculture method that uses microbial communities to enhance water quality and support aquatic species cultivation. Our research aims to delve into the pivotal role of aeration intensity within BFT systems, revealing its influence on microbial community structures, water quality, and nutrient cycling for L. vannamei culture. Three aeration levels were set with intensities of V75 (75 L/min), V35 (35 L/min), and V10 (10 L/min). The results showed that the lowest aeration intensity (V10) resulted in larger floc sizes and a reduction in the 2D-fractal dimensions, indicating a decreased overall structural complexity of the bioflocs. In addition, water quality parameters, including total ammonia nitrogen and nitrite, remained low across all treatments, highlighting the water-purifying capacity of biofloc. While protein and lipid contents in biofloc did not differ significantly among treatments, docosahexaenoic acid (DHA) levels were highest in the V75 treatment, suggesting that higher aeration promotes the accumulation of essential fatty acids. RDA analysis revealed that microorganisms like Ruegeria sp. and Sulfitobacter mediterraneus negatively correlated with ammonia and nitrite levels, suggesting their key role in converting ammonia to nitrite and nitrate in marine nitrogen cycles. The functional annotation of metagenomes across different aeration levels showed the similarly active roles of microorganisms in nitrogen metabolism and protein synthesis. In conclusion, while variations in aeration intensity affect floc size and the accumulation of essential fatty acids in biofloc, they do not significantly impact overall water quality or core microbial functions in L. vannamei aquaculture. Future research should focus on the effects of aeration strategies on microbial community dynamics and the integration of these data with performance metrics in L. vannamei. These insights can help optimize biofloc cultivation and enhance environmental sustainability in the aquaculture industry.

The liver of fish is an essential metabolic organ that also serves an immune regulatory role. In this study, we constructed a model of largemouth bass (Micropterus salmoides) infected with Nocardia seriolae by injection to explore the immune and antioxidant functions of the liver. The results showed that N. seriolae infection caused severe pathological changes in the liver, including cell necrosis, granuloma formation, and leukocyte infiltration. The level of mRNA expression of immune-related genes in the liver was significantly increased 2 days post-infection. Moreover, the combined analysis of transcriptome and metabolome showed that N. seriolae infection markedly affected liver metabolism, including glutathione metabolism, arginine and proline metabolism, arachidonic acid metabolism, as well as starch and sucrose metabolism. Additionally, multiple key biomarkers were identified as involved in regulating responses to N. seriolae infection, including arginine, glutathione, gpx, GST, PLA2G, GAA, and PYG. To further elucidate the regulatory effects of arginine on the immune and antioxidant processes in the liver, primary hepatocytes were isolated and cultured. The results demonstrated that arginine supplementation significantly reduced the expression of LPS-induced apoptosis-related genes (bax, cas3, cas8, and cas9) by up to 50% while increasing the expression of antioxidant genes (gpx, GST) by up to 700% at 24 h. Through the analysis of metabolic changes and immune responses in the liver following N. seriolae infection, combined with in-vitro experiments, this study elucidated the anti-apoptotic and antioxidant effects of arginine, revealing the immune response mechanisms in fish liver and laying the groundwork for using nutritional strategies to improve fish health.

This study examines the impact of the arginine/lysine ratio in feed on the growth, serum amino acids, arginine metabolism, and antioxidant capacity of juvenile largemouth bass (5.95 ± 0.02 g). Five isonitrogenous and isolipidic diets with varying arginine/lysine ratios were formulated and administered over an eight-week period. The results indicated that the treatments had no significant effect on protein efficiency ratio (PER), daily feed intake (DFI), or morphological indices of juvenile largemouth bass (p > 0.05). When the arginine/lysine ratio was 0.85 (2.25/2.65; 2.54/3.00), liver antioxidant capacity was maximized, and inflammatory factors were suppressed. Conversely, a ratio of 2.25/2.99 significantly reduced weight gain (WG) and specific growth rate (SGR) in juvenile largemouth bass, inhibited arginase activity, and increased serum total nitric oxide synthase (T-NOS) activity. When lysine was in excess (2.25/2.99 group), elevating arginine content (2.54/3.00 group) enhanced growth, antioxidant, and immune performance. Analysis of glutathione metabolism and innate immune-related pathway revealed that an optimal arginine/lysine ratio mitigates inflammatory damage induced by oxidative stress. An arginine/lysine imbalance significantly elevated liver malondialdehyde (MDA) content while reducing total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT) activities, and glutathione (GSH) content, thereby increasing the expression levels of inflammatory factors (IL1B, IL8, TGFB1, BAX). These findings demonstrate that an imbalance in arginine/lysine adversely affects the growth, metabolism, and antioxidant capacity of largemouth bass. When lysine is in excess, increasing the arginine content to achieve an arginine/lysine ratio of 0.85 alleviates the negative effects of antagonism, suggesting arginine supplementation may regulate oxidative damage caused by lysine excess.

Background/Objective: Over an eight-week period, this study assessed the influence of dietary carbohydrate levels on growth, metabolism, and immunity in Pacific white shrimp (Litopenaeus vannamei) raised within a biofloc technology (BFT) system. Methods: Five isonitrogenous and isolipidic diets, spanning carbohydrate levels from 11% to 47%, were evaluated. Results: The results showed that dietary carbohydrate significantly impacted both growth performance and feed utilization. The diet containing 38% carbohydrate yielded the best outcomes, resulting in the highest weight gain, specific growth rate, and an optimal feed conversion ratio in the shrimp. Hepatopancreatic metabolic analysis revealed that the shrimp adapted to diets high in carbohydrates through the upregulation of glycolytic enzymes (PK, PFK) and downregulation of gluconeogenic enzymes (PEPCK, G6Pase). By optimizing the water quality and supplementing microbial nutrition, L. vannamei in the BFT system exhibited enhanced dietary carbohydrate utilization and strengthened innate immunity. Specifically, SOD and CAT activities remained largely unaffected by varying carbohydrate levels. However, excessive carbohydrate intake still induced oxidative stress. The high-sugar group (47%) exhibited a significant increase in hemolymph MDA content (p < 0.05), with corresponding metabolic alterations observed in glucose, triglyceride, and total protein levels. On the basis of the results of this study, the BFT system may mitigate the adverse effects of a high-carbohydrate diet by enhancing lysosomal enzyme activity (e.g., ACP) and increasing total protein levels. Conclusions: These findings suggest that the BFT system enhances shrimp immunity and mitigates the potential adverse effects of imbalanced dietary components. Piecewise regression analysis determined the optimal dietary carbohydrate level for shrimp within the BFT system to be 31.44-31.77%.

An 8-week feeding trial was conducted to assess the effects of different dietary lipid levels on the growth performance, feed utilization, and body composition of juvenile kelp grouper Epinephelus moara. Six diets with varying lipid levels of 2.82%, 5.30%, 7.83%, 11.76%, 14.19%, and 16.32% (designated as CL1 to CL6) were carefully formulated. A cohort of 324 juvenile fish (initial body weight of 5.87 ± 0.09 g fish−1) were randomly divided into six groups with three replicates in each group. The results showed that weight gain (WG) significantly improved as the dietary lipid level increased to 7.83%, followed by a decline with further increases. Fish fed the diet with 7.83% lipids also exhibited the highest feed efficiency (FE) and protein efficiency ratio. Although daily nitrogen intake and daily energy intake varied, no significant differences in nitrogen retention and energy retention were detected among the groups. With the increase in dietary lipid levels, daily lipid intake and daily lipid gain significantly increased, but lipid retention showed a consistent decline. Additionally, the viscerosomatic index and intraperitoneal fat ratio and the lipid content of the whole body, dorsal muscle, and liver increased significantly with increasing dietary lipid levels. The hepatic glycogen content inversely decreased with the elevation in dietary lipid levels. The lowest total cholesterol content in the serum was detected in the 16.32% dietary lipid treatment. According to the second-order polynomial regression analysis of WG and FE, a dietary lipid level of 6.56–9.31% was optimal for the growth performance and feed efficiency of juvenile kelp grouper.

In this study, soluble dietary fiber (SDF) was extracted from Sargassum horneri via enzymatic hydrolysis and evaluated for therapeutic efficacy in male ICR mice (5-6 weeks, 17-18 g) with intestinal injury induced by cyclophosphamide (CTX; 80 mg/kg/day intraperitoneal injection for 5 days). Animals received daily intragastric gavage of SDF at low- (250 mg/kg), medium- (500 mg/kg), or high-dose (1000 mg/kg) concentrations for 7 days. Biochemical assays demonstrated that SDF enhances antioxidant capacity in colon tissues and reduces serum lipopolysaccharide (LPS) levels (P < 0.05). The up-regulation of tight junction proteins (Claudin-1, Zonula Occludens-1, P < 0.05) further confirmed the reinforcement of the intestinal barrier. Untargeted metabolomics revealed that SDF restores CTX-induced metabolic disorders by modulating the kynurenine pathway, optimizing histidine metabolism, and restoring glycerophospholipid homeostasis. Notably, 16S rRNA sequencing indicated that SDF induces significant shifts in microbial ecology, characterized by increased probiotics (norank_f__Muribaculaceae, P < 0.05; Bacteroides, P < 0.05; Alloprevotella, P < 0.01). These findings highlight the intricate interplay between microbiota and metabolome in SDF-mediated intestinal protection, offering novel insights for developing functional foods to combat chemotherapy-associated gut toxicity.

This study explored the effects of docosahexaenoic acid-enriched phosphatidylcholine (DHA-PC) extracted from Clupea harengus roes on DHA/ eicosapentaenoic acid (DHA/EPA) deposition and health of Pacific white shrimp (Litopenaeus vannamei). Three diets containing 0 %, 1.5 % and 3.5 % DHA-PC were prepared. Shrimp with an initial weight of 1.59 +/- 0.04 g were used as the experimental subjects for a 4-week feeding trial. In terms of oxidative stress indices, DHA-PC elevated the activity of antioxidant enzymes (including superoxide dismutase (SOD), total antioxidant capacity (T-AOC), and reduced glutathione (GSH)) and gene expression in various tissues. Simultaneously, two doses of DHA-PC both downregulated the expression of immune genes (traf6, penaeidin and toll) in intestine. As for lipid metabolism, DHA-PC reduced serum and hepatopancreas lipid levels (triglyceride (TG), total cholesterol (T-CHO), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C)). Moreover, DHA-PC augmented the content of DHA and EPA in shrimp muscle. DHA-PC diminished the mRNA expression of lipid synthesis genes (fas and srebp), while upregulating the mRNA expression of fatty acid oxidation gene (cpt1). A total of 1773 lipid molecular species belonging to 4 categories and 44 lipid classes were identified in muscle lipidomics. Compared with the CON group, DHA-PC upregulated 136 lipid metabolites and downregulated 94 lipid metabolites, primarily focusing on PCs, phosphatidylethanolamines (PEs) and TGs. Moreover, DHA-PC improved the positioning of DHA and EPA in PC, PE, and TG glycerol backbone. In conclusion, DHA-PC from fish roes amalgamated the beneficial effects of DHA and PC, facilitating the deposition of DHA and EPA in muscle while enhancing the antioxidant stress resistance and immunity of shrimp. As an excellent supplement of n-3 long-chain polyunsaturated fatty acids (LC-PUFA), it can contribute to the healthy culture of shrimp and provide a high-quality protein source for humans.

The main objective of this experiment was to study the metabolism of arginine in juvenile largemouth bass (Micropterus salmoides). A total of 300 healthy fish (average weight of 25 ± 0.5 g) were randomly assigned to ten groups. Experimental fish were orally administered or intraperitoneally injected with 0.9

The investigation of geographical feed raw materials is crucial to maintain the sustainable development of aquaculture. Ensuring the intestinal health of aquatic animals is the key to improving the absorption and utilization rate of new protein sources. In the present study, a composite protein source derived from the sargassum enzyme-hydrolysate compound fish protein hydrolysate ("SFPH" in the experiment) was utilized to replace 0 %, 5 %, 10 %, 20 %, 30 %, and 40 % of fish meal protein, respectively. Pacific white shrimp (Penaeus vannamei) with an initial weight of 0.9 g was used as experimental model for an 8-week feeding trial. The results revealed that SFPH replacement reduced the width of intestinal microvilli, but the 5%SFPH group significantly increased intestinal wall thickness and microvilli height. Antioxidant indicators analysis revealed that when over 10 % of fish meal protein was substituted with SFPH, the total antioxidant capacity dramatically decreased. When SFPH replaced 40 % of fish meal protein, the mRNA expression levels of endoplasmic reticulum stress-related indicators (bip and atf4) significantly increased, as well as the genes associated with apoptosis (jnk, caspase 8 and caspase 3). The analysis of intestinal microbiota showed that the 5%SFPH group significantly increased the richness of intestinal microbiota and significantly increased the abundance of beneficial bacteria (Campilobacter, Patescibacter, Deferribacter and Halobacter). The 40%SFPH group significantly increased the abundance of pathogenic bacteria (Pseudomonas, Serratia, Rickettsia, Edwardsiella, and Veillonella). A total of 201 differential relative abundance metabolites were detected by metabolomics, among which the contents of succinate, oxidized glutathione and reduced glutathione were reduced in the 40%SFPH group. The differential metabolites were mainly enriched in cysteine and methionine metabolism, biosynthesis of amino acid and glutathione metabolism. Based on the integrated analysis of metabolomics and intestinal microbiota, changes in signal pathways such as amino acid metabolism and glutathione synthesis may be the main reasons for the high proportion of SFPH disrupting intestinal health. This study provides in-depth data on the reaction mechanisms of shrimp to seaweed protein, and also provides new directions for the improvement of seaweed protein in the future.

A 53-day experiment investigated the impact of varying dietary carbohydrate-to-lipid (C/L) ratios in biofloc technology (BFT) systems on the growth, feed efficiency, enzyme activity, and metabolism of Pacific white shrimp Litopenaeus vannamei, while also analyzing the microbial community structure and function in the biofloc. Five isonitrogenous and isoenergetic diets (C/L 1.0, 4.1, 6.2, 10.5 and 14.2, 29 % crude protein) were formulated, along with a control diet (35 % crude protein, 7 % lipid). In the groups with dietary C/L ratio of 4.1 and 6.2 group, shrimp showed improved nitrogen retention (NR), energy retention (ER), and higher trypsin activities, compared to the control group. As the C/L ratio increased from 1.0 to 10.5, haemolymph glucose levels increased significantly, while triglyceride and total cholesterol levels were highest at a C/L ratio of 4.1, subsequently decreasing significantly with further increases in the C/L ratio. Antioxidant enzyme activities (CAT and SOD) were elevated in the BFT groups, with the lowest malondialdehyde (MDA) levels observed at C/L ratios of 4.1 and 6.2. Pyruvate kinase (PK) and phosphofructokinase (PFK) activities increased with increasing C/L ratio, while phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) activities decreased. There were no significant differences in the microbial composition, function, or nutrient content of the bioflocs across BFT groups, all of which maintained water quality and provided supplemental nutrition for shrimp. Based on quadratic fitting of weight gain (WG) and specific growth rate (SGR), the optimal dietary C/L ratio for L. vannamei in biofloc systems ranged from 6.44 to 6.52. This study provides theoretical guidance for formulating low-protein and low-cost feeds for farming Litopenaeus vannamei in biofloc systems.

Soybean meal (SBM) prepared by soybean crushing is the most popular protein source in the poultry and livestock industries (Cai et al., 2015) due to its economic manufacture, high protein content, and good nutritional value. Despite these benefits, SBM contains various antigen proteins such as glycinin and β-conglycinin, which account for approximately 70% of the total proteins of the SBM and reduce digestibility and damage intestinal function (Peng et al., 2018). Treating SBM with proteases (neutrase, alcalase, and trypsin) or fermentation can eliminate these antigen proteins (Contesini et al., 2018). Because of its safety and rapid growth cycle, Bacillus strains are considered ideal for the fermentation industry (Yao et al., 2021). SBM fermented by Bacillus yields products with high nutritional value and low levels of antinutritional factors (ANFs), stimulating research in this area (Yuan et al., 2017). Kumari et al. (2023) demonstrated that fermentation with Bacillus species effectively degrades antigen proteins and increases crude protein content. The degradation of antigen proteins relies on protease hydrolysis. Low protease production is the major obstacle hindering the widespread use of microbial fermentation techniques.

Exogenous amino acid supplementation has become a nutritional strategy to improve the tolerance of whiteleg shrimp (Litopenaeus vannamei) to a high proportion of vegetable protein diets. In the present study, the effects of glycine in high-proportion fermented soybean meal (FSBM) feed for shrimp were verified. SBM fermented by Bacillus subtilis was used to replace 50%, 75%, and 100% of fish meal (FM), respectively. Concomitantly, 1% glycine was added to the diets containing FSBM. After an 8-week feeding trial, FSBM substitution significantly inhibited the growth parameters of shrimp, including weight gain rate (WGR) and specific growth rate (SGR). Glycine supplementation significantly alleviated the inhibition of growth performance induced by 50% FSBM substitution but not in the 75% and 100% FSBM substitution groups. Glycine significantly increased the level of glycine in the muscle. In addition, glycine supplementation improved the structure of hepatopancreas and increased the length of sarcomeres and myofiber density in muscle tissue. RT-qPCR results revealed that glycine inhibited the mRNA expression of smyhc1 and smyhc2. Further investigation revealed that glycine enhanced the antioxidant capacity in muscle tissue and inhibited the mRNA expression of immune genes, including traf6, toll, and lgbp, caused by FSBM substitution. In summary, the results indicated that appropriate glycine supplementation could ensure that 50% FSBM substitution of FM did not affect the growth performance of shrimp. Moreover, glycine may improve the structure of muscle tissue by enhancing antioxidant capacity and immunity. This study further emphasized the crucial role of glycine in the development of low FM feed for shrimp.

Continuing global warming intensifies the thermal stress suffered by fish, urgently necessitating effective mitigating techniques. This study aims to investigate the mechanisms by which astaxanthin alleviates oxidative stress and inflammatory damage induced by thermal stress. Under thermal stress, an increase in oxidative stress was observed in the myocytes of Micropterus salmoides, however, intervention of astaxanthin exerted a notable alleviating effect on oxidative stress. Evidence of thermal stress experiment on primary myocytes indicates that astaxanthin resists thermal stress by enhancing the activity of antioxidant enzymes, heat shock proteins and activating the antioxidant gene Nrf2. Further integrated multi-omics analysis revealed a significant upregulation of several antioxidant biomarkers, such as Glutathione (GSH), glutathione peroxidase (GPX) and glutathione S-transferase (GST). This study proposes the hypothesis that astaxanthin may enhance the GSH-dependent endogenous antioxidant enzyme system by activating the Keap1-Nrf2 signaling pathway. Notably, the supplementation of astaxanthin, compared to thermal stress alone, inhibited the expression of inflammatory factors and apoptosis-related genes, including TLR2, IL8, EIF4E, IL2RB, CASP3, and CASP9. These results, combined with the observed inhibition of the Toll-like receptor signaling pathway and the NF-κB signaling pathway, indicate that the TLR2/4-NF-κB signaling pathway plays a crucial role in mediating the alleviation of oxidative stress-induced inflammatory damage by astaxanthin. Furthermore, astaxanthin remodels amino acid and lipid metabolism under thermal stress, establishing an adaptive anti-thermal stress metabolic mechanism that encompasses both phase I and phase II metabolism. These findings offer novel insights into the mechanisms underlying astaxanthin-induced protection against oxidative stress and inflammatory damage.

Biofloc technology (BFT) enhances shrimp farming sustainability by improving water quality and reducing external feed inputs. While protein and lipid requirements for Penaeus vannamei in BFT systems are lower than in traditional systems, the optimal lipid level under low-protein diets remains unclear. This study examined the effect of low-protein diets with varying lipid levels on the growth, metabolism, and nutrient cycling of P. vannamei in biofloc systems. Five diets with fixed 29 % protein and lipid levels ranging from 5 % to 13 % were tested, with the control diet containing 35 % protein and 8.6 % lipid. Results showed that lipid levels did not significantly affect biofloc composition, but shrimp growth was optimized at 10.04 %-10.14 % lipid. Higher lipid levels boosted lipase and CAT activity, while amylase, trypsin and SOD activities remained unchanged. Higher lipid levels (11 %-13 %) improved nitrogen retention and utilization. Microbial analysis indicated Leucothrix mucor played a role in nitrogen assimilation, with increased expression of genes related to the DNRA pathway in 9 % lipid group. Although carbon budgeting was unaffected by lipid levels, carbon loss remained high among all groups, potentially due to incomplete utilization of glycolysis and acetate metabolism or shrimp molting. This study highlights the potential for optimizing nutrient strategies in BFT systems to improve feed efficiency and support sustainable shrimp farming.