Nitrite is a major toxicant in aquaculture, impairing fish growth and health. While selenium (Se) is known for its antioxidant and immune-enhancing properties, its protective role against nitrite-induced gill damage remains unclear. The objective of this work was to assess the effect of dietary Se on nitrite-induced gill injury in grass carp and to elucidate the associated mechanisms. Results indicated that nitrite exposure induced gill injury through oxidative stress, mitochondrial dysfunction, and ferroptosis. Dietary Se provided a protection against this injury. Its primary effects included enhancing antioxidant defense and improving ion transport homeostasis in the gill. In addition, dietary Se mitigated mitochondrial dysfunction, ferroptosis, and inflammatory responses, ultimately attenuating gill damage induced by nitrite exposure. The protection was mediated primarily through the SP1/GPX4 pathway signaling, which functions to suppress ferroptosis. These findings provided a theoretical foundation for using Se as a dietary supplement to enhance nitrite tolerance in aquaculture.

Selenium (Se) is a vital trace element necessary for fish growth and health. This research aimed to elucidate the beneficial impacts of coated sodium selenite (CSS) on sub-adult grass carp muscle and compared effects of CSS and sodium selenite (SS). A total of 450 healthy fish with an initial average body weight of 687.33 ± 1.15 g were randomly assigned to six groups. Fish in these groups were fed experimental diets supplemented with graded levels of CSS (0.028, 0.25, 0.50, 0.75, and 1.00 mg/kg Se) and one diet containing SS at 0.50 mg/kg Se, respectively, for an 8-week feeding trial. Results indicated that optimal CSS increased body length and Se concentrations in muscle and hepatopancreas (P < 0.05). The accumulated Se further up-regulated the expressions of selenoproteins (such as gpx1 and selp), which collectively improved antioxidant capacity (such as glutathione peroxidase [GPX] activity and L-glutathione [GSH] content]) and mitochondrial quality (such as fusion, biogenesis, and respiratory chain) (P < 0.05). These alterations improved muscle fiber development by upregulating the expression of genes related to protein synthesis (pi3k, akt, and s6k1) and extracellular matrix synthesis (col1α1, smad2, smad4, tgf-β1, and phd) (P < 0.05). Interestingly, at the 0.50 mg/kg Se supplementation, CSS and SS showed similar growth and muscle development, but different responses in signaling pathways, implying that CSS may confer additional physiological benefits. Overall, dietary Se could enhance muscle growth in sub-adult grass carp by dual mechanisms: enhancing antioxidant defenses and improving mitochondrial quality.

Skeletal muscle constitutes the main consumable part of fish, and its quality and physiological integrity are critical to the sustainable advancement of aquaculture. This investigation focused on the consequences of dietary myo-inositol (MI) deficiency on muscle homeostasis in grass carp (Ctenopharyngodon idella) using six experimental diets with varying amounts of MI: 35 (basal diet, deficient group), 98, 195, 292, 389, and 487 mg/kg. Fish were fed for 8 weeks. Transcriptome analysis of grass carp muscle tissue was first performed, revealing that efferocytosis and the pentose phosphate pathway (PPP) were among the primary metabolic pathways affected by MI intervention. Further investigation demonstrated that MI administration within the range of 195-487 mg/kg effectively activated the PPP, as indicated by significantly increased activities of two key enzymes in its oxidative branch-glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH). This enzymatic activation led to enhanced NADPH production. The consequent rise in NADPH levels resulted in decreased intracellular ratios of NADP+/NADPH and GSH/GSSG, reflecting a strengthened reductive cellular environment and thereby improving the capacity to scavenge reactive oxygen species (ROS). Furthermore, MI reduces cell death in muscle tissue and enhance macrophage-mediated efferocytosis. Concurrently, MI inhibits the polarization of macrophages towards pro-inflammatory phenotypes by enhancing lysosomal function. Therefore, the inclusion of appropriate levels of MI (195-389 mg/kg) in the diet is beneficial for maintaining muscle tissue homeostasis in grass carp.

This experiment used combination of electronic tongue, electronic nose, and gas chromatography mass spectrometry methods to analyze the impact of dietary isoleucine (Ile) on the flavor in grass carp muscle. Key findings include: Ile improved the sweetness and umami and reduced sourness and bitterness of the flesh. Ile inhibited sulfide and the relative content of volatile compounds like nonanal and hexanal in muscle. Second, Ile enhanced the content of adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate, and decreased the content of hypoxanthine. Furthermore, Ile raised the content of fatty acid (FA) and the enzymes related to FA synthesis. Based on the above results, it can be concluded that dietary Ile improved flesh flavor by reducing the relative content of volatile compounds like 1-octen-3-ol and increasing the content of FA and nucleotides, providing valuable insights into improving flesh quality.

Aquaculture, the farming of aquatic organisms such as fish, mollusks, crustaceans, and algae, continues to be one of the most viable methods to feed the growing world population. Currently, aquatic animals, mainly fish, mollusks, and crustaceans, account for 72% of aquaculture, 89% of which is used for human consumption, providing 7.7% of the total animal protein ingested by humans. Aquatic animal protein not only is rich in essential amino acids but also has high digestibility. Moreover, aquaculture is an efficient and sustainable way of producing animal protein, partially due to the higher feed efficiency of aquatic animals, lower energy consumption, and fewer environmental impacts. The speed of aquaculture development is highly dependent on the aquafeeds. Accordingly, many dietary and environmental factors could affect the aquatic animal protein deposition and essential amino acid composition. Sustainable aquaculture also faces many challenges, such as environmental, climate, and resource factors, which are also discussed.

The skeletal muscle system was established during the embryonic stage, a process that determines the number of muscle fibers and affects skeletal muscle functionality. Energy metabolism plays a vital role in the growth, development, and maturation of skeletal muscle, making it crucial to maintain metabolic homeostasis. L-arginine is recognized as an essential nutrient involved in numerous physiological processes and serves as a significant regulator of animal development. However, there is limited information available about its mechanisms involved in muscular development during embryogenesis. Therefore, we utilized zebrafish (Danio rerio) as a model organism to investigate the effects of arginine on skeletal muscle development, energy metabolism, and mitochondrial homeostasis during embryogenesis. Our findings demonstrate that arginine enhances the development of zebrafish embryo, as evidenced by increased survival and hatching rates, body length, and spontaneous movement. We subsequently demonstrated that arginine promotes skeletal muscle development by improving muscle structure and content, upregulating the expression of myogenic regulatory factors, and enhancing the skeletal muscle contractile function in zebrafish. Furthermore, arginine promotes energy metabolism (improved phosphocreatine system, glucose and lipid metabolism, and tricarboxylic acid cycle) of skeletal muscle via the CAMKK2/AMPK/SIRT3/PGC-1 alpha signaling pathway, thereby increasing ATP levels, ultimately enhancing locomotor performance. Arginine also augments mitochondrial function by promoting mitochondrial biogenesis, mitochondrial dynamics, and mitochondrial autophagy. Additionally, arginine increased the antioxidant capacity through the Nrf2 signaling pathway, and improved anti-apoptotic of zebrafish embryos. In summary, our present study reveals a potential mechanism that by which arginine promotes the locomotor function of zebrafish embryos, where it improves skeletal muscle development and function, modulates energy metabolism, and mitochondrial homeostasis. These findings which provides a fundamental theory o for understanding arginine's role in regulating the healthy development of fish skeletal muscles.

Fumonisin B1 (FB1) is a common mycotoxin present in aquaculture feeds, which has been demonstrated to impair the growth performance of cultured animals and induce intestinal oxidative damage. However, while effective nutritional interventions remain limited. This study aimed to investigate whether the natural antioxidant silymarin (SIL) could alleviated FB1-induced growth inhibition in juvenile grass carp (Ctenopharyngodon idella). The 720 fish (10.92 ± 0.01 g) were randomly distributed into four groups: control, 4 mg/kg FB1, 60 mg/kg SIL, and 4 mg/kg FB1 + 60 mg/kg SIL. Each group was fed the designated diet for 30 days. The data indicated FB1 exposure significantly reduced growth performance, caused severe villus damage, and compromised intestinal structural integrity. Notably, SIL supplementation markedly alleviated these adverse effects. SIL restored the activities of brush border and digestive enzymes and reversed FB1-induced disruption of tight junctions, adherens junctions, and desmosomal structures. Importantly, SIL effectively enhanced intestinal antioxidant capacity, restored the expression of mitochondrial respiratory chain components (e.g., Ndufv1, Uqcrc2, and Cox4), decreased reactive oxygen species production and endoplasmic reticulum (ER) damage, and suppressed the activation of the Mlck/Mlc pathway, thereby maintaining cytoskeletal stability and junctional integrity. However, SIL did not significantly reduce intestinal FB1 residues or sphingolipid accumulation. These findings suggested that the alleviation of FB1-induced intestinal structural damage by SIL may be associated with its antioxidant activity, which targeted the alleviation of mitochondrial and ER damage. This highlighted the potential of SIL as an antioxidant to alleviate mycotoxin-related hazards in aquaculture. This study provided new insights and data support for the development of relevant functional feeds.

Nitrite is a ubiquitous stressor in intensive aquaculture. This study aimed to investigate the protective mechanism of dietary coated sodium selenite (CSS) on grass carp muscle tissue damage mediated by nitrite exposure, with a specific focus on mitochondrial-endoplasmic reticulum contact (MERC) stability. Grass carp were maintained for 8 weeks on diets supplemented with CSS at five selenium (Se) levels (0.028, 0.25, 0.50, 0.75, and 1.00 mg/kg), after which they were subjected to a 96-h nitrite exposure. Results indicated that Se mitigated nitrite-induced disturbances in blood parameters and muscle quality deterioration. Additionally, Se maintained MERC integrity, potentially through the mitigation of mitochondrial calcium (Ca2+) overload. It also down-regulated the endoplasmic reticulum (ER) stress markers and apoptosis-related factors. These results suggested that Se supplementation could serve as an effective preventive strategy against muscle quality degradation and muscle damage induced by nitrite sterss in aquaculture.

Although corn gluten meal (CGM) is recognized for its high protein content, contains almost no anti-nutritional factors, and is considered a potential source of bioactive peptides, its effects on protein metabolism and digestive absorption capacity in herbivorous fish remain to be studied. This study investigated the effects of replacing SBM with CGM on intestinal digestion-absorption and systemic amino acid metabolism in sub-adult grass carp. Five isonitrogenous and isolipidic diets containing graded levels of corn gluten meal (CGM) were formulated: diet 1 (0.00%, control, replacing 0% soybean meal), diet 2 (6.03%, replacing 40%), diet 3 (9.04%, replacing 60%), diet 4 (12.06%, replacing 80%), and diet 5 (15.07%, replacing 100%). A total of 450 sub-adult grass carp (728.16 +/- 1.51 g) were randomly allocated to 15 experimental units. The five diets were assigned to the units (three replicates per diet) and fed to the fish for a 63-day feeding trial. Fish were randomly allocated to five dietary treatments. Results showed that 40% and 60% replacement did not significantly affect production performance (final body weight, weight gain, specific growth rate, feed efficiency). However, key morphometric parameters (visceral somatic index, intestinal length index, intestinal somatic index) were significantly depressed in replacement groups compared to the control (P < 0.05). The highest activities of intestinal brush border enzymes, digestive enzymes, and amino acid transporters (P < 0.05), along with the highest concentrations of serum free amino acids and muscle amino acids (P < 0.05), were observed in the control and 40% replacement groups, likely due to enhanced amino acid transporter expression in intestine and muscle. The 40% replacement level did not significantly alter muscle crude protein content, the protein levels of key molecules in the muscle synthesis pathway (TOR, 4E-BP1, S6K1), muscle IGF-1 content, and the related gene expression. Similarly, protein and gene expression in the degradation pathway (MAFbx, MuRF1, FoxO1, FoxO3a) were not significantly affected at 40% replacement but exhibited a dose-dependent increase at higher levels. In conclusion, 40% replacement of SBM with CGM supports sub-adult grass carp growth by preserving intestinal function and amino acid metabolism.

This study evaluated the effect of riboflavin (VB2) on growth performance and its ability to alleviate hypoxia-induced hepatic inflammation in sub-adult grass carp (Ctenopharyngodon idella), as well as the underlying mechanisms. A total of 450 grass carp (402.16 ± 1.01 g) were randomly distributed into 18 tanks and fed one of six experimental diets with varying VB2 concentrations (0.47, 1.96, 3.45, 4.97, 6.47, and 7.98 mg/kg) for 60 d, followed by a 96 h hypoxia stress experiment. The experimental results showed that, compared with VB2 deficiency (0.47 mg/kg VB2) group, the 1.96 to 7.98 mg/kg VB2 groups enhanced the percent weight gain, specific growth rate, and feed efficiency, and exerted a growth-promoting effect on grass carp (P < 0.001). In the hypoxia group, the supplementation of VB2 (3.45-6.47 mg/kg) increased hepatic VB2 content, D-amino acid oxidase, and glutathione reductase activities (P < 0.001), thereby enhancing the function of the flavoprotein. Furthermore, the 3.45 to 6.47 mg/kg VB2 groups reduced the activities of serum aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and alkaline phosphatase (P < 0.05), thereby mitigating hepatic damage induced by hypoxia. The 3.45 to 4.97 mg/kg VB2 groups increased hepatic ATP content (P < 0.001), while reducing cytoplasmic mitochondrial DNA copy number under hypoxia stress. Compared with the VB2 deficiency group, the 4.97 mg/kg VB2 group promoted the fluorescence intensity of VDAC1, TOMM20, and OPA1 under hypoxia stress (P < 0.001), thereby improving mitochondrial structure and function. Riboflavin also mitigated hypoxia-induced hepatic inflammation. Dietary 3.45 to 7.98 mg/kg VB2 reduced the expression of pro-inflammatory factors such as il-1β, tnf-α and ifn-1, while 3.45 to 6.47 mg/kg VB2 groups increased the expression of anti-inflammatory cytokine such as il-4, il-10, and tgf-β (P < 0.05). Dietary 4.97 mg/kg VB2 reduced the expression of p-STING, p-TBK1, p-IRF3, and p-P65 (P < 0.05). Finally, using percent weight gain, D-amino acid oxidase (D-AAO), and alanine aminotransferase (ALT) for secondary regression analysis, VB2 requirements for sub-adult grass carp were determined to be 5.39, 5.11, and 5.49 mg/kg, respectively. Overall, this study provides a theoretical basis for the role of VB2 in alleviating hypoxia-induced hepatic inflammation and for formulating diets for sub-adult grass carp.

Intestinal inflammation threatens aquaculture by impairing fish health, while antibiotic overuse raises resistance concerns. Fraxetin, a natural coumarin with anti-inflammatory properties, emerges as a promising sustainable alternative. This study investigated the protective effects of dietary fraxetin against DSS-induced acute enteritis in grass carp (Ctenopharyngodon idella) under short-term effects. Following a 60-day feeding trial with fraxetin supplementation (0, 3.9, 7.9, 15.8, 31.5, and 63.1 mg/kg diet), thirty grass carp of comparable weight to those at the end of growth were selected, and DSS was injected to induce enteritis and sampled 24 h later. The results showed that 7.9-15.8 mg/kg of fraxetin could significantly reduce the morbidity of enteritis in grass carp. Appropriate fraxetin alleviated endoplasmic reticulum stress by suppressing the expression of PERK, GRP78, ATF4, CHOP, and XBP1 genes and/or proteins in intestinal cells. 3.9-63.1 mg/kg fraxetin enhances innate immune function and inhibits peroxidase activity by increasing lysozyme and complement C3/C4 levels. 3.9-7.9 mg/kg fraxetin upregulates the gene and protein expression of the regulatory T cell transcription factor FOXP3 and downregulates helper T cell type 17 transcription factors ROR gamma 1 and gamma 2 gene expression. At the same time, appropriate fraxetin increased the levels of anti-inflammatory factors (IL-10, IL-4/13 A, and IL-4/13B) and inhibited pro-inflammatory mediators (IL-6, IL-18, and TNF-alpha). Furthermore, fraxetin inhibited NF-kappa B, JAK2, and STAT3 protein phosphorylation levels by reducing them. In addition, 7.9 mg/kg of fraxetin was beneficial for structural optimization of gut microbiota. In conclusion, adding an appropriate amount of fraxetin in the diet can alleviate intestinal inflammation and improve intestinal disease resistance of grass carp. In addition, the optimal dietary fraxetin levels were evaluated to be 7.61 mg/kg based on linear regression analysis of MPO.

Hypoxia is a common environmental stressor in aquaculture systems, significantly jeopardizes the health of fish species. This study aimed to explore the effects of coated ferrous sulfate on hypoxia-induced inflammation in the hepatopancreas of grass carp and the underlying mechanisms. Seven dietary iron levels were tested, including uncoated ferrous sulfate (UC-Fe: 73.5 mg/kg, actual level 72.21 mg/kg) and dietary iron concentrations (NC: 0, C-Fe: 40, 60, 80, 100, 120 mg/kg, actual levels of 22.23, 38.75, 58.97, 79.12, 98.44, 117.58 mg/kg). Sub-adult grass carp with an initial body weight of 405.76 ± 0.86 g were fed the experimental diets for 8 weeks, followed by a 96-h hypoxia challenge. Results showed that coated ferrous sulfate significantly improved growth performance, reduced serum LDH, GPT, and GOT activities, and decreased ROS, MDA, and 8-OHdG levels in the hepatopancreas while increasing SOD activity and GSH content under hypoxia, thereby alleviating hypoxia-induced oxidative damage. Additionally, coated ferrous sulfate elevated hemoglobin concentration in the blood under hypoxic conditions, concomitantly augmented iron and ferritin contents in the serum and hepatopancreas, and upregulated the expression of iron metabolism-related indicators (TFR2, HIF-1α, DMT1, RGMc), thereby facilitating iron absorption, storage, and transportation. Under hypoxic conditions, coated ferrous sulfate increased the protein expression levels of mitochondrial respiratory chain complexes II, III, and V, reduced cytoplasmic mtDNA content, and elevated ATP levels in the hepatopancreas. These regulatory effects modulated the cGAS-STING and ATP-P2X7 signaling pathways to attenuate hypoxia-induced inflammation. Coated ferrous sulfate exhibited superior efficacy compared to uncoated ferrous sulfate in improving growth performance, enhancing antioxidant capacity, and alleviating hypoxia-induced inflammation. Finally, based on PWG and blood hemoglobin concentration, the dietary requirement of coated ferrous sulfate for sub-adult grass carp was ascertained to be 56.46 mg/kg (for growth) and 56.97 mg/kg (for hypoxia resistance), respectively.

Bacterial infections compromise fish physiological homeostasis by impairing barrier function and metabolic organs, posing a persistent challenge in intensive aquaculture. Silymarin (SLM) is a plant-derived flavonoid complex obtained from Silybum marianum, widely recognized for its multifunctional pharmacological and bioactivity. However, its regulatory role under stress induced by bacterial pathogens in aquatic animals remains poorly understood. This study explored the impact and potential mechanisms of dietary SLM on intestinal barrier function and liver protection in juvenile grass carp. Fish (24.2 ± 0.1 g) were randomly assigned to six groups and fed diets containing 0, 20, 40, 60, 80, or 100 mg/kg SLM for 70 days. Subsequently, the fish were challenged with Aeromonas hydrophila (A. hydrophila) for 6 days. Optimal SLM supplementation (1) alleviated intestinal damage by upregulating tight junction proteins and downregulating myosin light chain kinase (MLCK); (2) reduced liver pro-inflammatory cytokines, inhibited lipopolysaccharide (LPS) translocation, and suppressed activation of the Toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88) signaling pathway; (3) mitigated liver inflammation by inhibiting the phosphorylation of key nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathway proteins and downregulating nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome components; (4) decreased liver oxidative stress while enhancing antioxidant capacity and improving liver function; and (5) modulated gene expression related to metabolic enzymes and transporters in the intestine and liver. Dietary SLM improved gut-liver health by supporting barrier function, reducing inflammation, and enhancing metabolic and antioxidant responses, indicating its promise for nutritional use in aquaculture.

Nitrite is a toxic substance widely present in aquaculture water environments. This study explored the impact of vitamin K on liver pathology in grass carp (Ctenopharyngodon idella) challenged with nitrite. Grass carp received diets with six vitamin K concentrations (0 + sulfamethoxazole, 0, 1, 2, 3, and 4 mg/kg) for 60 days, then endured a 96-h nitrite stress test. Our results showed that vitamin K enhanced growth performance and reduced damage indicators in adult grass carp, including weight gain percentage (PWG), glutamic-pyruvic transaminase (GPT), and methemoglobin (MetHB). At the cellular level, vitamin K upregulated the expression of Golgi apparatus matrix protein 130 (GM130) and acid sphingomyelinase (ASM) in hepatocytes, increased sphingomyelin and ceramides levels, and repaired stress-damaged cell membranes. At the tissue level, vitamin K promoted liver regeneration by upregulating repair markers alpha-smooth muscle actin (alpha-SMA) and transforming growth factor-beta (TGF-beta) and boosting collagen deposition via growth arrest-specific 6 (GAS6) and its receptor AXL. Additionally, vitamin K alleviated nitrite-induced hepatocyte apoptosis, potentially through upregulating the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway to maintain mitochondrial homeostasis. With PWG and GPT as indicators, the optimal vitamin K requirements for normal and nitrite resistance of adult grass carp were 1.88 and 1.94 mg/kg, respectively. This study assessed the effects of nitrite exposure on grass carp liver, elucidated the potential mechanism by which vitamin K mitigates such damage, and provided novel insights for alleviating nitrite stress in fish.

In high-density intensive aquaculture systems, enteritis has emerged as a critical health concern. In bony fish, the intestine serves as the core organ of the digestive system and plays an important part in maintaining physiological homeostasis. Disruption of intestinal barrier integrity can lead to metabolic disturbances, inflammatory responses, and progressive impairment of intestinal barrier function. Myo-inositol (MI), a vitamin-like nutrient, exerts notable beneficial effects on the structural integrity of physical barriers and non-specific immunity in various aquatic species. A total of 450 adult grass carp (Ctenopharyngodon idella) (704.84 ± 0.91 g) were randomly divided into 6 treatments (3 replicates per treatment) to receive six levels of dietary MI (35 [basal diet], 98, 195, 292, 389, and 487 mg/kg). Following an 8-week feeding period, intestinal inflammation was induced using dextran sulfate sodium (DSS). Compared with the MI supplement group, the results demonstrated that MI deficiency (basal diet) suppressed intestinal development in adult grass carp, aggravated intestinal structural damage in DSS-induced enteritis, and reduced the number of intestinal goblet cells (P < 0.001). Moreover, MI deficiency increased the incidence of DSS-induced enteritis (P < 0.001). Mechanistically, MI deficiency caused sustained NF-κB p65 activation by disrupting early endosome formation and impairing TNFR1 internalization (P = 0.015). This cascade ultimately triggered cell apoptosis and exacerbated intestinal inflammation. Collectively, these findings revealed how MI contributes to the maintenance of intestinal barrier function and enhanced understanding of its role in regulating intestinal health in grass carp.

Rosemary-derived triterpene acids (TAs), primarily composed of ursolic acid, oleanolic acid, and betulinic acid, exhibit multiple bioactive properties. However, their effects on lipid metabolism and the underlying regulatory pathways remain unclear. This study investigated the effects of dietary supplementation with TAs on the growth performance, digestive and absorptive function, and hepatic lipid metabolism in juvenile grass carp (Ctenopharyngodon idella). In this trial, 2,160 juvenile grass carp (average weight 13.04 ± 0.02 g) were randomly allocated to six dietary treatments, each comprising six replicates with 60 fish per replicate. Fish were fed diets supplemented with increasing concentrations of TAs (0, 58.80, 179.30, 261.90, 312.00, and 390.00 mg/kg) for 70 d. At the end of the trial, relevant samples were collected for subsequent analyses. The results demonstrated that dietary supplementation with TAs significantly increased specific growth rate (SGR), whole-body crude protein (CP) levels, and protein retention value (PRV) in juvenile grass carp, while reducing whole-body ether extract (EE) levels. Moreover, dietary supplementation with TAs significantly enhanced the activities of intestinal digestive enzymes and brush-border enzymes, thereby improving the digestive and absorptive capacity of juvenile grass carp. In the liver, dietary supplementation with TAs markedly inhibited lipid synthesis while promoting lipid utilization. The effects of TAs on lipid metabolism were associated with activation of the hepatic farnesoid X receptor (FXR) pathway, involving peroxisome proliferator-activated receptor alpha (PPARα) and sterol regulatory element-binding protein 1 (SREBP-1). Furthermore, TAs modulated the gut–liver axis by inhibiting the intestinal FXR–sphingomyelin phosphodiesterase 3 (SMPD3)–ceramide pathway, which may contribute to reduced hepatic lipid deposition. Quadratic regression analysis showed that the optimal dietary TAs supplementation levels were 245.00 mg/kg (SGR), 218.33 mg/kg (intestinal lipase activity), and 267.64 mg/kg (hepatic hormone-sensitive lipase activity). The addition of TAs to the diet improved growth performance, digestive and absorptive capacity, and liver lipid utilization in juvenile grass carp. This work reveals the potential application of TAs in aquaculture and provides a theoretical basis for the development of functional feed additives.

D-mannose, a biologically active monosaccharide, is pivotal for protein glycosylation and immune regulation, yet its role and underlying mechanisms in enhancing fish enteritis resistance remain inadequately characterized. This study aimed to investigate the effects of dietary D-mannose on gut microbiota structure and resistance to dextran sodium sulfate (DSS)-induced enteritis. All 1800 juvenile grass carp were randomly assigned to 6 treatment groups and fed diets supplemented with graded levels of D-mannose (0.52, 1.75, 3.02, 4.28, 5.50 and 6.78 g/kg) for 70 days, followed by a DSS-induced enteritis challenge. The results revealed that D-mannose improved gut microbial structure and short-chain fatty acid levels, suggesting a potential enhancement in enteritis resistance. In the DSS-induced enteritis model, D-mannose supplementation significantly reduced enteritis incidence and mitigated intestinal histopathological damage, as evidenced by improved epithelial cell arrangement and reduced lamina propria edema. Mechanistically, D-mannose enhanced intestinal antimicrobial capacity and modulated the balance of pro-inflammatory and anti-inflammatory cytokines, which was associated with the regulation of CD4+ T cell differentiation to maintain Th1/Th2 and Th17/Treg subset homeostasis. Additionally, D-mannose alleviated intestinal pyroptosis by suppressing the NLRP3 inflammasome pathway, which may be mediated by preserving lysosomal integrity and inhibiting cathepsin B activation. Collectively, these findings demonstrate that dietary D-mannose effectively enhances fish enteritis resistance and intestinal immune function, with mechanisms involving the modulation of gut microbiota, regulation of T cell differentiation, and inhibition of lysosome-dependent NLRP3 inflammasome-mediated pyroptosis. This study provides a theoretical basis and practical guidance for the application of D-mannose as a potential antibiotic alternative in aquafeeds to mitigate enteritis in grass carp.

Despite rapid expansion, the aquaculture industry faces the dual challenges of finite fishmeal resources and heightened disease susceptibility under intensive farming. To advance sustainability, plant proteins are being actively developed as fishmeal alternatives due to their lower cost. This study investigated the effects of replacing fishmeal with enzymatically hydrolyzed corn protein (EHCP) on intestinal digestion, absorption, and inflammatory response in juvenile yellow catfish (Pelteobagrus fulvidraco). The substitution of 6% EHCP enhanced the growth performance and intestinal function of juvenile yellow catfish. Following the Vibrio mimicus challenge, EHCP alleviated intestinal inflammation by promoting immune cell differentiation and suppressing pro-inflammatory cytokine expression. Mechanistically, EHCP promoted CD4+ T-cell differentiation into key effector subsets (Th1, Th2, Th17, and Treg) via JAK-STAT and NF-κB signaling pathways, thereby maintaining intestinal homeostasis. The optimal EHCP substitution levels (6.38 and 6.40%) provide an efficient and economically viable innovative solution for sustainable aquafeed development.

As a major farmed fish, grass carp (Ctenopharyngodon idella) is an important source of dietary protein, but lipid metabolism disorders threaten its health and aquaculture efficiency. This study investigated the impact of histidine on hepatic liposynthesis, catabolism and lipophagy in grass carp and elucidated the potential molecular pathways involved. The grass carp were fed diets containing graded histidine concentrations: 1.08 (basal diet), 2.91, 5.87, 8.83, 11.85, and 14.79 g/kg for 63 days. The results indicated that histidine deficiency significantly increased the hepatosomatic index and induced hepatic lipid accumulation. Mechanistic studies suggest that histidine deficiency-induced hepatic lipid accumulation may be associated with two interrelated pathways: (1) Dysregulation of lipid metabolism: regulation of TOR and its downstream SREBP1 and PPAR alpha to regulate lipid synthesis and catabolism, respectively, may be related to FTCD signaling. (2) Impaired lipophagy: disruption of autophagy and lysosomal function via the TOR-mediated TFEB pathway leading to defective lipid droplet clearance possibly involved with FTCD signaling. This study demonstrated that histidine deficiency disrupted hepatic lipid homeostasis by impairing lipid metabolism and lipophagy activity, ultimately leading to pathological lipid accumulation and hepatomegaly in grass carp. This study offers new perspectives on how histidine influences lipid metabolism and underscores its critical role in supporting proper liver function, providing both theoretical and practical foundations for developing sustainable aquaculture nutrition strategies to enhance aquatic protein production.

L-arginine (Arg) is an essential and multifunctional amino acid for the body, and has the ability to modulate lipid homeostasis; however, the specific underlying mechanism remains unclear. Grass carp was used as a model to explore the effects of Arg on hepatopancreas lipid metabolism and its potential mechanism. A total of 450 healthy grass carp (661.60 ± 1.00 g) were randomly assigned to six groups with different Arg levels (3.51, 7.01, 10.51, 14.01, 17.51, and 21.01 g/kg) for 9 weeks. There were three replicates per each group, each holding 25 fish. These findings indicated that Arg deficiency caused lipids to accumulate in the hepatopancreas of grass carp. Supplementation of Arg promoted lipid metabolism by significantly reducing lipid droplet number, fatty acid synthetase (FAS) activity, 4-hydroxynonenal (4-HNE) expression, lipogenesis genes (elvol5, elvol2, fad, scd-1, acc, fas, and lxra) and protein (SREBP1 and PPARγ) levels (P < 0.05), while increasing the hormone-sensitive lipase (HSL), adipose triglyceride lipase (ATGL), and acyl-CoA synthetase (ACS) activities, fatty acid β-oxidation genes and protein levels (P < 0.05). The improvement of hepatopancreas lipid metabolism by Arg can be achieved through the following ways: 1) Arg mitigated endoplasmic reticulum (ER) stress in the hepatopancreas by down-regulating the mRNA relative expression levels of chop, xbpl, elol2, grp78, ire1, perk, atf4, and atf6, as well as the protein expression levels of GRP78, p-PERK, and IRE1 (P < 0.05); 2) Arg protected mitochondrial function by upregulating the expression level of proteins related to the mitochondrial respiratory chain complex, and by enhancing mitochondrial quality regulation system, thereby increasing liver ATP levels (P < 0.001); 3) Arg increased the hepatopancreas antioxidant function by activating the nuclear respiratory factor 2 (Nrf2)/Kelch like ECH associated protein 1 (Keap1) pathway (P < 0.05); 4) Arg enhanced the link between mitochondria and the ER by increasing the expression of Ca2+ transporters and proteins (SERCA1, VAPB, ACAT1, VDAC1, MCU, and GRP75) related to mitochondria-associated ER (MAM) (P < 0.05), thereby promoting lipid metabolism. These results highlight the importance of the interaction of mitochondria and ER in alleviating lipid accumulation by Arg and supporting the potential of Arg as a dietary supplement for regulating metabolic homeostasis in animals.