To investigate the impact of tea polyphenols on the health of Pelteobagrus fulvidraco under ammonia stress, a total of 480 juvenile P. fulvidraco were divided into four groups receiving tea polyphenols supplemented diets at 0 mg kg-1 (C group), 200 mg kg-1 (L group), 400 mg kg-1 (M group) and 600 mg kg-1 (H group) for 56 days. Ammonia stress was applied from days 28 to 56. The results showed that intestinal histological damage was alleviated in the L and M groups under ammonia stress. In the M group, the levels of total antioxidant capacity and Nrf2, HO-1 and Occludin were the highest. Regarding ferroptosis-related genes, DMT1, FTM and FPN1 exhibited their highest expression in the L group, while TF, TFR1, FTL, SLC7A11 and GPX4 showed their highest expression in the M group. FTH demonstrated its highest expression in the H group. Furthermore, the expression of ACSL4 in the L and M groups was significantly lower than that in the C group. Intestinal microbiome analysis revealed enhanced microbial diversity in the tea polyphenol-added groups, accompanied by reduced relative abundance of dominant phylum Fusobacteriota and genus Cetobacterium compared to the C group. These results suggested that dietary supplementation of 200-400 mg kg-1 tea polyphenols could alleviate ammonia-induced intestinal ferroptosis and histological damage, as well as protect intestinal health by regulating the compositional structure and diversity of the intestinal microflora. Specifically, the 400 mg kg-1 dose exerted the most comprehensive protective effects. This study provides mechanistic insights into the development of tea polyphenol-based anti-ammonia feed additives for P. fulvidraco aquaculture.

The purpose of this research was to evaluate the effect of dietary lipid levels on ovarian development for Pacific white shrimp(Litopenaeus vannamei). Five levels of lipid were prepared to contain 8.87 %, 10.14 %, 11.01 %, 12.88 % and 14.65 %, respectively. The feeding expreiment lasted for fourteen weeks. The results evidenced that 11.01 % lipid diet group showed the maximum n-3 LC-PUFA in ovary among all treatments. The highest proportion of ovarian maturation to stage IV and stage V occurred at the treatment with 11.01 % lipid. The treatment with 11.01 % lipid showed the highest TG, TCHO, E2, 5-HT, VTG in hemolymph, and VTG in ovary among all treatments. Dietary 11.01 % lipid notably up-regulated the expression of genes relevant to ovary development such as pcna, sesn, vg1, vgr and vtg in ovary, dietary excessive 10.14 % lipid can notably up-regulated the expression of protein related to ovary development such as Vtg / alpha-Tubulin and Hsd3b1 / alpha-Tubulin. The highest expression of brain and ovarian genes related to molting such as sad, rxr, e75, hr3 and hr4 existed at the treatment with 11.01 % lipid. Dietary lipid significantly affected lipid metabolism-related gene expression. In conclusion, dietary 11.01 % lipid contributed to the synthesis of hepatopancreatic exogenous vitellinogen, and transportation to the ovary via the vitellogenin receptor, further promoting the production of ovarian endogenous vitellinogen.

The replacement of fishmeal with plant protein is a key strategy for sustainable aquaculture, but reduced feed intake and digestive efficiency remain major constraints. This study evaluated the effects of dietary dimethyl-β-propiothetin (DMPT) supplementation on feed intake, digestive function, antioxidant capacity, and intestinal microbiota in narrow-clawed crayfish (Pontastacus leptodactylus) fed an all-plant protein diet. Three isonitrogenous and isolipidic diets were formulated: a plant protein diet (PPD), an animal protein diet (APD), and a PPD supplemented with 0.5% DMPT. After a 4-week feeding trial, results showed that PPD significantly reduced feed intake and digestive enzyme activities compared to APD, whereas DMPT supplementation restored feed intake to a level comparable to APD, maintained growth-related parameters at intermediate levels, and significantly enhanced α-amylase (AMS), lipase (LPS), and trypsin (TPS) activities. Additionally, DMPT markedly improved hepatopancreatic antioxidant capacity, as indicated by increased total antioxidant capacity (T-AOC), glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD) levels, without affecting muscle composition or intestinal morphology. Microbiota analysis revealed that DMPT altered community structure, increased Bacillota abundance, and promoted microbial network stability. Overall, DMPT supplementation effectively mitigates the limitations of plant protein diets and supports the replacement of animal protein in crayfish aquafeeds.

Ammonia is more problematic in intensive aquaculture because it can be toxic to aquatic animals. The intestine is critical for nutrient assimilation and growth, but it is highly susceptible to contaminants due to direct, prolonged aquatic contact. However, the mechanism by which chronic ammonia exposure affects nutrient assimilation in juvenile yellow catfish (Pelteobagrus fulvidraco) remains unclear. This study explored the impact of chronic ammonia exposure on growth and intestinal nutrient assimilation in juvenile yellow catfish. Juvenile yellow catfish were exposed to 0, 2.5, 5.0, 7.5, and 10.0 mg/L total ammonia nitrogen for 56 days. The study revealed that chronic ammonia stress (CAS) significantly inhibited the growth of juvenile fish (P < 0.05), elevated plasma ammonia, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and cortisol levels, and impaired intestinal structure and enzyme activity (digestive and brush border enzymes). Furthermore, CAS significantly suppressed the GH/IGF-1/Akt/mTOR signaling pathway (P < 0.05) and downregulated the expression of amino acid transporters. It also significantly increased PKC beta II protein expression and hindered the accumulation of oligopeptide transporters in the plasma membrane (P < 0.05). In addition, significant inhibition of the glucagon b (GCGB)/proprotein convertase subtilisin/kexin type 1 (PCSK1)/glucagon-like peptide-2 (GLP-2) pathway (P < 0.05) may contribute to a significant reduction in intestinal microvilli growth (P < 0.05). In summary, these results highlight the detrimental effects of CAS on the growth and intestinal nutrient assimilation capacity of yellow catfish, providing valuable insights into the importance of maintaining water quality for aquaculture management.

This study aimed to analyze the beneficial impacts of dietary sodium lactate (SLA) on growth, metabolism, and ammonia resistance in juvenile yellow catfish (Pelteobagrus fulvidraco) under chronic ammonia stress. In an 8-week experiment, 360 healthy juveniles (1.64 ± 0.03 g) were assigned to 4 groups (3 replicates, 30 fish/replicate), fed either a basal diet or a 1.00% SLA-supplemented diet with or without 2.5 mg/L total ammonia nitrogen (T-AN) exposure. The results showed that dietary SLA supplementation effectively ameliorated growth inhibition and impaired feed efficiency caused by chronic ammonia stress. At the digestive level, SLA supplementation significantly enhanced the activities of intestinal lipase and pepsin, with no significant change in amylase activity. In addition, dietary SLA positively regulated serum biochemical profiles, improved hepatic antioxidant capacity, and alleviated oxidative damage induced by long-term ammonia exposure. At the molecular level, SLA modulated the expression of hepatic glucose metabolism-related genes, reversed the inhibitory effect of chronic ammonia stress on muscle growth-related gene expression, and downregulated the growth-suppressive gene mstn. Collectively, dietary SLA can effectively mitigate the adverse effects of chronic ammonia stress on juvenile yellow catfish by improving digestive function, regulating metabolic homeostasis, and alleviating hepatic oxidative damage and ammonia toxicity. This study supports the application of SLA as a functional feed additive in aquaculture.

Naringenin (NGN), a flavonoid compound abundantly found in citrus fruits, exhibits anti-inflammatory, antioxidative activities, and hypolipidemic properties. However, nowadays, NGN is mainly used to inhibit the occurrence of viral diseases in aquatic animals by injection as an immunosuppressant, and its safety and other physiological effects as a feed additive have not been sufficiently investigated. This study elucidates how naringenin (NGN) mitigates the negative impacts exerted by a high-fat diet (HFD) on Largemouth bass (Micropterus salmoides) from hepatic and intestinal perspectives. After an 8-week feeding trial, the NGN groups had a significant effect on growth performance compared to the HFD group, and significantly decreased the lipid content of the whole body. Secondly, NGN significantly decreased the levels of triglycerides and total cholesterol in serum compared with the HFD group, down-regulated the lipogenesis-related genes, and significantly upregulated the lipolysis-related genes. Furthermore, hepatic injury markers alanine transaminase and aspartate transaminase were also significantly decreased. Additionally, NGN significantly enhanced the antioxidant capacity of the liver, down-regulated the gene expression of pro-inflammatory factors, and up-regulated the antiinflammatory factors. There were remarkable changes in the structure of the gut microbiota, where the biomarker of the Na1 group was Dyella, and the main ones in the Na2 group were Asinibacterium, Methylovirgula, Mesorhizobium, and Meiothermus. The function of the gut microbiota in the NGN was more enriched in the fatty acid biosynthesis pathway compared to the high-fat diet. To conclude, the supplementation of NGN to HFD can significantly reduce hepatic lipid deposition and alleviate liver damage, as well as improve gut health status. Among them, the addition of 0.007 % naringenin exhibited a better effect. The results of this study will be used to help reduce the negative effects of an HFD within the aquaculture sector and hold the potential to be regarded as a promising eco-friendly feed additive for aquaculture.

The study aimed to analyze the beneficial effects of dietary sodium lactate (SLA) on growth, metabolism, and ammonia tolerance in juvenile yellow catfish (Pelteobagrus fulvidraco) under chronic ammonia stress. Over an 8-week experiment, 360 healthy juvenile yellow catfish (1.64 ± 0.03 g) were assigned to 4 groups (3 replicates, 30 fish/replicate) fed either a basal diet or 1.00% SLA-supplemented diet with or without 2.5 mg/L total ammonia nitrogen (T-AN) exposure. The results showed that dietary supplementation of SLA can improve growth performance and feed utilization under chronic ammonia stress: weight gain rate increased from 335.85% to 413.55%; specific growth rate increased from 2.63%/d to 2.92%/d; feed conversion rate decreased from 1.59 to 1.44. It can also increase intestinal digestive enzyme activity: lipase increased from 25.10 to 32.84 U/gprot; pepsin increased from 6.32 to 9.23 U/mgprot (amylase activity showed no significant difference). Serum biochemical parameters were modulated by SLA: lactate increased from 1.24 to 2.17 mmol/L; pyruvate increased from 0.18 to 0.32 mmol/L; lactate dehydrogenase activity increased from 185.36 to 268.45 U/L; total protein increased from 15.58 to 18.83 mg/mL; albumin increased from 4.92 to 6.93 g/L; serum ammonia content decreased from 0.87 to 0.53 mmol/L; alanine aminotransferase decreased from 8.08 to 4.68 U/L; aspartate aminotransferase decreased from 17.32 to 8.40 U/L. Liver antioxidant capacity was enhanced: superoxide dismutase increased from 53.69 to 84.53 U/mgprot; catalase increased from 56.07 to 76.27 U/mgprot; malondialdehyde decreased from 66.57 to 52.13 nmol/gprot. Acute ammonia stress survival rate increased from 94.44% to 96.67%. Furthermore, In addition, SLA supplementation significantly up-regulated the mRNA expression levels of glycometabolism-related genes (pepck, pcxa, pcxb, hk1, gk, pkm and pfkp) in the liver of yellow catfish. Meanwhile, SLA supplementation reversed the ammonia stress-induced inhibition of the expression of muscle growth-promoting genes (myod, myog, erk, mek and myf5), and down-regulated the expression of the growth-inhibiting gene mstn. Under non-stressed conditions, SLA supplementation also up-regulated the expression of multiple growth-related genes (myod, myog, erk, mek, myf5 and igf-1). In conclusion, dietary sodium lactate supplementation can effectively improve the growth performance and ammonia nitrogen tolerance of juvenile yellow catfish under chronic ammonia nitrogen stress by regulating metabolism, enhancing digestive function, and alleviating oxidative damage and ammonia nitrogen toxicity. This study provides a theoretical basis for the application of sodium lactate as a functional feed additive in aquaculture.

This study aimed to explore whether Lactobacillus amylovorus (LA) mitigates acute ammonia-induced intestinal damage in yellow catfish (Pelteobagrus fulvidraco). A 14-day experiment used 360 healthy fish (initial body weight: 6.26 ± 0.05 g), randomly assigned to 4 groups (3 replicates, 30 fish/replicate): control (CON, 0 mg/L T-AN), ammonia exposure (AM, 125 mg/L T-AN), LA supplementation (LA, 0 mg/L T-AN + LA), and LA + AM (125 mg/L T-AN + LA). LA was sprayed onto commercial feed at 1 × 108 CFU/g. The results showed that the LA + AM had a significantly higher survival rate (78.33 ± 12.58% vs. 40.00 ± 5.00% in AM, P < 0.05), reduced serum/intestinal ammonia levels, alleviated intestinal villi breakage/shedding, and mitigated oxidative stress (lower ROS, MDA; higher SOD, CAT, GSH, T-AOC, P < 0.05). LA regulated inflammation (downregulated il-1β/il-6/il-8/tnf-α/nf-κb mRNA and IL-1/IL-6/p-NF-κB p65 protein; upregulated IL-10 protein, P < 0.05), enhanced intestinal barrier function by upregulating tight/adherens junction (zo-1, claudin-1, occludin) gene/protein (ZO-1, E-cadherin) expression (P < 0.05), and modulated gut microbiota (increased Lactobacillus/Cetobacterium abundance, decreased Plesiomonas/Proteobacteria, elevated α-diversity, P < 0.05). In conclusion, LA protects yellow catfish from ammonia-induced intestinal damage via antioxidant, anti-inflammatory, barrier-enhancing and microbiota-modulating effects, promising as a nutritional strategy to alleviate ammonia stress in intensive aquaculture.

Ammonia, a ubiquitous and highly toxic aquatic contaminant threatening aquatic organisms, can readily cause intestinal damage. Yet, the underlying mechanism by which ammonia triggers intestinal ferroptosis in fish remains elusive and requires systematic investigation. The objective of this study was to investigate the sub-chronic toxic effects of ammonia on the intestine of juvenile yellow catfish (Pelteobagrus fulvidraco) and to elucidate the regulatory mechanism underlying ammonia-induced intestinal injury via the NADPH oxidase/reactive oxygen species (ROS)/ferroptosis axis. Healthy juvenile yellow catfish (initial weight: 3.47 +/- 0.01 g) were randomly assigned to five total ammonia nitrogen (TAN) treatments (0, 2.5, 5.0, 7.5, and 10.0 mg/l), with three replicates of 30 fish per group, and exposed for 56 days. Vas2870 (a NADPH oxidase inhibitor) and Ferrostatin-1 (Fer-1, a ferroptosis inhibitor) were applied for mechanistic intervention. Ammonia exposure significantly decreased survival rate (P < 0.05), elevated ammonia concentrations in serum and intestinal tissue (P < 0.05), increased intestinal permeability, and induced oxidative stress through NADPH oxidase-mediated ROS overproduction (P < 0.05). It also triggered intestinal ferroptosis, as evidenced by iron accumulation, mitochondrial dysfunction, glutathione depletion, and enhanced expression of lipid peroxidation-related indicators (P < 0.05). Inhibition of NADPH oxidase or ferroptosis markedly mitigated the intestinal damage caused by ammonia (P < 0.05). These results demonstrate that the NADPH oxidase/ROS/ferroptosis axis mediates sub-chronic ammonia-induced intestinal toxicity in juvenile yellow catfish. This study provides novel insights into the toxicological mechanisms of ammonia in teleosts and offers theoretical support for aquatic environmental risk assessment and pollution control.

This study investigated the effects of selenium-enriched Bacillus subtilis on the growth performance, antioxidant capacity, intestinal health, and metabolism of mandarin fish (Siniperca chuatsi) juveniles. The experiment included a control group (Y), a Bacillus subtilis group (BS), an inorganic selenium group (Se), and three groups with low, medium, and high concentrations of selenium-enriched B. subtilis (S1, S2, S3) in a 30-day feeding trial. The results showed that selenium-enriched B. subtilis had no significant effect on the final average body weight or specific growth rate of the fish, but significantly reduced the viscerosomatic index. In terms of antioxidant capacity, the total antioxidant capacity, superoxide dismutase, and glutathione peroxidase activities were significantly increased in the S2 and S3 groups, while catalase activity in the S3 group was significantly higher than that in the Se group. Intestinal morphology analysis revealed that the high-concentration selenium-enriched probiotic (S3) caused villi damage and intestinal wall hyperplasia. Gut microbiota analysis indicated that selenium-enriched B. subtilis increased the abundance of Bacteroidetes and Firmicutes, and decreased the abundance of potential pathogens such as Proteobacteria; however, microbial diversity and richness were significantly reduced in the S3 group. Metabolomic analysis revealed upregulation of various anti-inflammatory and antioxidant metabolites and downregulation of cholesterol-related metabolism in the S3 group. In conclusion, an appropriate concentration of selenium-enriched Bacillus subtilis (recommended dosage: 5.31 & times;109 CFU/kg) can effectively enhance antioxidant capacity and improve intestinal microbiota structure in mandarin fish, whereas excessively high concentrations may cause intestinal damage.

Itaconate (ITA), a tricarboxylic acid (TCA) cycle metabolite known to modulate lipid metabolism in mammals, poultry, and certain aquatic species, has not been documented in largemouth bass (Micropterus salmoides). This study formulated six diets with graded ITA levels (0%, 0.05%, 0.1%, 0.2%, 0.4%, 0.8%) and fed them to largemouth bass for 8 weeks, to evaluate effects on growth, liver lipid accumulation, and lipid metabolism mechanisms. Results showed 0.05% ITA enhances growth performance, while ITA > 0.2% significantly reduces hepatosomatic index and abdominal fat weight. Diets with 0.4% and 0.8% ITA significantly increased high density lipoprotein and decreased total cholesterol and triglycerides, though ITA supplementation reduced weight gain rate. No adverse effects were observed on liver injury markers or antioxidant parameters, indicating ITA as a feed additive has a favorable safety profile and effectively supports lipid reduction and liver protection. Metabolomic analysis revealed 0.8% ITA significantly reduced 48 liver metabolites related to fatty acid catabolism, attributed to accelerated beta-oxidation pathway flux and rapid substrate consumption, enhancing liver lipid catabolism. Transcriptomic analysis showed 0.8% ITA downregulated glycolysis-related genes (pgk1, eno1a, etc.) and upregulated glycogen synthesis genes (pgm1, gys1), TCA cycle-oxidative phosphorylation (OXPHOS) genes (idh3b, sdhdb, etc.), and PPAR signaling pathway genes (insra, pik3r3b, etc.), suggesting altered liver energy metabolism via inhibited glycolysis, enhanced glycogen synthesis, and initiated fatty acid oxidation. q-PCR confirmed 0.8% ITA upregulated fatty acid degradation genes (acsl1a, cpt1ab, etc.) and TCA cycle-OXPHOS genes (idh3b, aco1, etc.) by activating PPAR signaling pathway genes (pparg, rxrgb). These findings indicate ITA enhances fatty acid beta-oxidation through the PPAR signaling pathway, providing a potential metabolic approach for fish fatty liver disease prevention.

The narrow-clawed crayfish (Pontastacus leptodactylus), a non-native species accidentally introduced into China's Irtysh River Basin, has formed a wild population with aquaculture potential, but its natural diet and protein utilization remain poorly understood. This study investigated its feeding ecology and digestive responses to protein sources to support ecological assessment and feed formulation. Intestinal contents and muscle samples from wild crayfish were analyzed using eDNA metabarcoding and fatty acid signature analysis. In vitro digestibility of 10 protein ingredients was evaluated with crude digestive enzyme extracts, and a 4-week trial compared an all-plant-protein diet (PPD) with an all-animal-protein diet (APD). eDNA indicated an omnivorous diet dominated by planktonic taxa, especially Rotifera, and fatty acid biomarkers suggested contributions from diatoms, dinoflagellates, phytoplankton, zooplankton, and benthic organisms. Soybean meal and soy protein concentrate showed high dry matter digestibility, whereas fishmeal and krill meal had high crude protein digestibility and amino acid release. Compared with PPD, APD increased feed intake, apparent nutrient digestibility, hemolymph nutritional indicators, villus height, and intestinal trypsin and lipase activities; however, intestinal integrity was preserved in both groups, and most intestinal antioxidant indices did not differ significantly. These findings indicate that animal proteins enhance nutrient utilization in P. leptodactylus, while selected plant proteins may serve as partial alternatives.

Ammonia stress (AS) constitutes a significant environmental challenge that impedes aquaculture development. In this investigation, histomorphology assessments, physiological, and biochemical parameter analyses, and multiomics approaches were employed to elucidate the impact of acute AS on yellow catfish (Pelteobagrus fulvidraco). Findings indicated that serum ammonia concentrations exhibited a dose-dependent increase, correlating with the intensity and duration of stress. As the primary detoxification organ, the liver facilitates ammonia clearance by upregulating genes involved in glutamine and ureagenesis (glutamine synthase [gs], carbamoyl-phosphate synthase [cps], ornithine transcarbamylase [otc], argininosuccinate lyase [asl], argininosuccinate synthase [ass], arginase [arg]), thereby promoting glutamine and ureagenesis while consuming glutamate, argininosuccinic acid, aspartic acid, arginine, and adenosine triphosphate (ATP). Physiological and biochemical data revealed that AS significantly elevated serum glucose, liver triglyceride (TG), and total cholesterol (TC) levels. Histological examination demonstrated a marked reduction in liver glycogen stores alongside a progressive accumulation of lipid droplets proportional to stress severity, suggesting activation of liver glycogenolysis coupled with suppression of lipolysis. Integrative transcriptomic and metabolomic analyses indicated a reprograming of liver energy metabolism characterized by enhanced glycogenolysis and suppressed lipogenesis: liver glycogen content decreased, key glycolytic gene expression (hk1, pdhx) was downregulated, and tricarboxylic acid (TCA) cycle flux was diminished due to decreased cs expression. Concurrently, transcription of fatty acid β-oxidation enzymes (acsbg1, cpt1) was suppressed, leading to palmitic acid accumulation and impaired lipid-derived energy production. Nonetheless, reorganization of carbon flux through upregulation of mdh2 and idh1 facilitated pyruvate utilization in the TCA cycle, promoting NADH generation and sustaining oxidative phosphorylation, as evidenced by increased ATP turnover and content. This study elucidates the metabolic response to AS via increased glycogenolysis. Optimizing liver glycogen reserves serves as a nutritional strategy to enhance ammonia tolerance. Targeted regulation of key genes (pygl, pk, mdh2, idh1) to promote glycogen–pyruvate metabolism may mitigate ammonia toxicity effects and improving aquaculture productivity.

High-fat (HF) diets are widely used in aquaculture to reduce feed costs, but they often lead to hepatic steatosis, oxidative stress, and reduced environmental tolerance in carnivorous fish. This study evaluated whether dietary rosiglitazone (RO; 10 mg·kg−1) alleviates HF (18% fat) diet-induced metabolic dysfunctions in juvenile largemouth bass (Micropterus salmoides). Fish were fed a control diet (10% fat), an HF diet (18% fat), or an HF + RO diet for 8 weeks. RO supplementation reversed HF-induced dyslipidemia by lowering plasma triglyceride (TG) and total cholesterol (T-CHO) while elevating high-density lipoprotein cholesterol (HDL-c), and it reduced intraperitoneal fat and whole-body lipid (p < 0.05). RO also mitigated hepatic vacuolization and decreased plasma alanine aminotransferase (ALT) (p < 0.05) and aspartate aminotransferase (AST) (p > 0.05) activities. Antioxidant capacity was enhanced by RO, as indicated by increased glutathione (GSH), catalase (CAT), and total antioxidant capacity (T-AOC), together with reduced malondialdehyde (MDA), and accompanied by upregulation of nrf2, downstream antioxidant genes, and downregulation of keap1 (p < 0.05). Moreover, RO suppressed HF-induced endoplasmic reticulum (ER) stress (grp78, eif2α, chop) and pro-inflammatory genes (tnfα, il-1β, nf-κb), while upregulating il-10 (p < 0.05). Gut microbiota analysis showed RO-mediated enrichment of Firmicutes and short-chain fatty acid-producing genera (Faecalibaculum, Dubosiella). Importantly, RO significantly reduced mortality during a 96 h acute ammonia challenge (p < 0.05). Collectively, these results demonstrate that dietary rosiglitazone mitigates HF diet-induced hepatic oxidative stress and metabolic dysregulation through Nrf2 activation, anti-inflammatory effects, and microbiota modulation, providing a potential strategy to enhance HF feed utilization and environmental stress resilience in carnivorous fish. Further studies on dose optimization and residue safety are warranted.

This study investigated the interventional effects of dietary itaconic acid (ITA) on high-fat diet (HFD)-induced lipid deposition in largemouth bass (Micropterus salmoides) and the underlying mechanisms. Results showed that ITA supplementation significantly alleviated HFD-induced growth performance inhibition, as indicated by increased weight gain rate, increased specific growth rate, and reduced feed conversion ratio. ITA supplementation effectively reversed the HFD-induced increase in the hepatosomatic index, intraperitoneal fat ratio, serum triglycerides, total cholesterol, low-density lipoprotein/high-density lipoprotein ratio, hepatic lipid droplet accumulation, and hepatocyte vacuolation. Importantly, ITA ameliorated HFD-induced impairment of antioxidant capacity and reduced liver alanine aminotransferase and aspartate aminotransferase activities. Liver metabolomics revealed that ITA reduced levels of 20 fatty acids, 14 acylcarnitines, and 13 glycerides, suggesting enhanced fatty acid oxidation and reduced lipid esterification. Transcriptome sequencing and q-PCR validation demonstrated that ITA activated the AMPK/mTOR pathway, upregulating autophagy-related genes (prkaa1, ulk2, map1lc3a, sqstm1) and lysosomal biogenesis-related genes (ap3s2, igf2r, lgmn, ctso), thereby enhancing autophagic-lysosomal flux and promoting lipid degradation. In conclusion, ITA reduces hepatic lipid accumulation by synergistically activating autophagy and lysosomal biogenesis, thereby facilitating the oxidative degradation of fatty acids within lysosomes. This study provides a theoretical basis for the application of ITA as a functional feed additive in aquaculture.

Nonionic ammonia (NH3) in water is toxic, ammonia intoxication increases susceptibility to pathogens, and threaten the survival and development of fish. The study endeavors to propose a novel mechanism for ammonia detoxification by observing alterations in biomolecules and metabolites in liver of yellow catfish exposed to ammonia stress (AS) for 96 h. This study conducted an in-depth analysis of the serum and liver of fish subjected to 0.72 mg/L NH3 for 96 h. Results revealed elevated serum ammonia levels, compromised serum antioxidant system, disrupted biochemical indexes, and severe liver damage. Liver transcriptomic analysis revealed 156 down-regulated and 55 genes up-regulated differentially expressed genes (DEGs) after AS. KEGG and GO enrichment analysis found that DEGs mainly concentrated in autophagy and mTOR signaling pathways. We examined the autophagy under AS at the molecular, protein and cellular levels by qRT-PCR, Western blot, and ultrastructural observations, respectively. The results showed that the autophagy mediated by mTOR under AS can be divided into two stages: the inhibition stage from 0 to 72 h and the autophagy activation stage from 72 to 96 h. Additionally, we demonstrate that activating autophagy through rapamycin enhances the survival rate when exposed to 3.6 mg/L NH3. Liver metabolomics revealed 278 significantly down-regulated and 31 significantly up-regulated differential metabolites (DEMs) after 96 h AS. Enrichment analysis showed that these DEMs were mainly concentrated in "arginine biosynthesis" and "valine leucine isoleucine biosynthesis". We also found that the expression of genes related to urea and glutamine synthesis (UGS) in the liver increased significantly after AS, indicating that the detoxification of ammonia necessitates the utilization of substrates and intermediate metabolites essential for UGS.

Ammonia generated from amino acid metabolism is a cytotoxin that can adversely affect cell function and overall health and potentially lead to cellular toxicity and death due to its accumulation. Previous studies have shown that acute ammonia intoxication (AI) can increase the intestinal C. somerae abundance, hinting at a possible involvement of C. somerae in the host's reaction to AI. Nonetheless, the precise mechanism through which C. somerae mitigates the effects of AI is uncertain. This research elucidated the metabolic mechanism of transplanting Cetobacterium somerae ceto (CSC) to assist the host in managing AI. Our results suggest that (I) AI resulted in impaired ureagenesis pathway. This was manifested by elevated levels of ammonia in the blood, liver, and intestines, along with decreased urea levels. (II) Supplementing orally with live CSC facilitated its colonization in the intestines, mitigating AI by reversing depletion of intestinal argininosuccinic acid (ARA) and promoting ureagenesis. (III) CSC synthesized ARA from aspartate and asparagine through the asnA-ansA/B-argG gene cluster. Additionally, CSC assimilated fumaric acid and malic acid from the environment, dampening the degradation of ARA by CSC’s fumA-fumB-argH gene cluster. (IV) Live CSC provided ARA support for ureagenesis in the intestine and liver, reducing endogenous ammonia levels of pseudo-sterile yellow catfish. (V) Supplementation of ARA decreased systemic ammonia levels by promoting ureagenesis. Inhibiting the expression of argininosuccinate lyase in the liver through RNA interference can impede arginine synthesis, thereby eliminating the ammonia-lowering effect of ARA. In summary, this study found that the role of probiotics in enhancing the host's resistance to AI depends on the function of ARA generated by CSC. AI can lead to depletion of ARA and interrupting ureagenesis, while CSC-produced ARA supplements ureagenesis in the liver and intestines, facilitating ammonia detoxification into urea.

The study explores how activating autophagy in yellow catfish under chronic ammonia stress (CAS) can boost growth and improve ammonia detoxification, addressing the serious threat of ammonia stress on fish survival and disease susceptibility in aquatic settings. Yellow catfish (Pelteobagrus fulvidraco) weighing 2.35 +/- 0.13 g were divided into three groups over an 8-week period: CON group without ammonia exposure, AM group exposed to 50 mg/L total ammonia nitrogen (T-AN), and AM+RAPA group fed diets with 3 mg/100 g rapamycin under 50 mg/L T-AN. Dietary rapamycin (DR) can alleviate growth retardation, liver structural damage, inflammation, apoptosis, decreased detoxification capacity, and reduced survival rate caused by CAS. Additionally, DR can mitigate autophagy inhibition induced by CAS. Metabolomics analysis revealed that activation of autophagy by DR significantly alleviated the glutamate, aspartate n-acetyl-l-glutamate, ornithine, argininosuccinate, and citrulline levels in the liver induced by CAS. This suggests that autophagy activation can supplement these metabolites involved in urea and glutamine synthesis, thereby promoting ammonia detoxification. In conclusion, liver autophagy is a vital mechanism for ammonia detoxification as it facilitates the synthesis of urea and glutamine. Moreover, it offers a theoretical foundation for addressing the negative effects of chronic ammonia exposure in aquaculture.

Ammonia causes stress, inhibits fish growth, and damages tissues and organs. The muscle proliferation contributes to more than 50 % of the growth of fish. This study aimed to investigate the effects of acute ammonia stress on muscle damage, reactive oxygen species (ROS) production and scavenging, and endoplasmic reticulum stress (ERS) in yellow catfish (Pelteobagrus fulvidraco). In this study, yellow catfish were exposed to three concentrations of ammonia (0, 25, and 125 mg/L) for 96 h. The results showed that acute ammonia stress resulted in the deterioration of plasma biochemical parameters, histopathological injury, and oxidative damage in the muscle. In addition, ammonia stress led to the overproduction of muscle ROS, which may be partially related to the activation of the muscle NADPH oxidase (NOX) family. Ammonia stress reduces the ability to scavenge ROS, which may be partly related to the inhibition of the muscle antioxidant system. Ammonia stress leads to ERS, which may be related in part to the activation of muscle-activating transcription factor 6 (ATF6), inositolrequiring enzyme 1 (IRE1)/X-box binding protein 1 (XBP1), and protein kinase RNA-activating-like ER kinase (PERK)/eukaryotic translation initiation factor 2 alpha (eIF2 alpha)/transcription factor 4 (ATF4) pathways. In conclusion, the present study provides evidence for the study of muscle toxicity induced by ammonia stress in freshwater fish and provides a reference for the healthy culture of yellow catfish.

It is very important to evaluate the growth tolerance threshold of fish under long-term low ammonia exposure for water quality management in aquaculture. This study employed a sequential method to evaluate the tolerance of hybrid carp to both acute and chronic ammonia exposure. In stage 1, we estimated the effects of acute high ammonia stress on hybrid carp and based on linear interpolation (y = 0.0047x - 0.4659, where R2 = 0.9448, with y representing cumulative mortality and x representing ammonia concentration), the 96-h LC50 was determined to be 206.38 mg/L of total ammonia (TA). In stage 2, the long-term low ammonia exposure ranges (< 0.001 (control), 1.03 (LC50/200), 2.05 (LC50/100), 4.11 (LC50/50), and 8.21 (LC50/25) mg/L TA) were determined based on 96-h LC50 value, and then a 6-week experiment was performed. The results showed that elevated ammonia concentration (> 1.03 mg/L TA) significantly reduced food intake. The growth performance was inhibited at ammonia concentrations above 1.03 mg/L TA, while survival rate decreased at ammonia concentrations above 4.11 mg/L TA. The lack of free amino acids (arginine, leucine, aspartic acid, and glutamine) not only affect the fish growth, but also inhibits the key enzymes (arginase and argininosuccinic acid lyase) activity in urea cycle, resulting in a decrease in ammonia detoxification ability. Even exposure to low concentration of ammonia (2.05 mg/L TA) can reduce the activity of antioxidant enzymes (superoxide dismutase and catalase), causing liver damage and inflammation. Long-term low ammonia exposure reduces intestinal microbiota richness and diversity while increasing relative abundance of harmful bacteria, such as Leifsonia, Aeromonas, Erysipelothrix, and Acinetobacter. And the increase in relative abundance of beneficial bacteria such as Cetobacterium may be a coping strategy against ammonia toxicity. We recommend against exposing hybrid carp to ammonia concentrations exceeding 1.03 mg/L TA for prolonged periods of time.