As a precursor to creatine, guanidinoacetic acid (GAA) is widely recognized to enhance growth performance and flesh quality of animals, but the underlying molecular mechanism remains unclear. This study evaluated the effects of dietary GAA supplementation on growth performance, textural properties, and flavor constituents in gibel carp CAS V (Carassius gibelio, CAS V). A total of 300 healthy gibel carp (5.01 ± 0.13 g) at 42 d of age were assigned randomly to 12 tanks (3 replicates per group, 25 fish per replicate). Fish were fed with a basal diet supplemented with graded levels of GAA (0.00, 0.03%, 0.06%, and 0.12%) for 10 weeks. Results demonstrated that GAA supplementation significantly enhanced the specific growth rate (SGR) and crude protein content in gibel carp (P < 0.05). It also enhanced muscle physicochemical attributes by increasing water holding capacity and hardness, along with boosting glycogen content and free glutamate level (P < 0.05). Mechanistically, GAA promoted myofiber development by upregulating protein and gene expression of myogenic regulatory factors (MRFs), leading to increase myofiber density and a higher frequency of myofibers with diameters between 20 and 40 μm (P < 0.05). Furthermore, GAA facilitated collagen synthesis to improve muscle hardness by activating the transforming growth factor-beta 1 (TGF-β1)/mothers against decapentaplegic homolog (SMADs) signaling pathway, upregulating transcript levels of tgf-β1, col1α1, col1α2, and smad3 (P < 0.05). Additionally, GAA increased inosine monophosphate (IMP) content in muscle (P = 0.015), which was associated with enhanced expression of AMPD1 protein and upregulation of the adsl, pkm, and ckm genes (P < 0.05). In conclusion, dietary GAA supplementation enhanced flesh quality of gibel carp via improving growth performance, nutrient deposition, texture characteristics, and flavor components.

Diet form is increasingly recognized as a welfare-relevant factor in intensive aquaculture, yet the effects of feed cooking on fish behavioral and physiological welfare remain poorly characterized. Juvenile southern catfish (Silurus meridionalis; 6.18 ± 0.52 g) were reared for 6 weeks in an indoor recirculating aquaculture system and fed either raw grass carp (Ctenopharyngodon idella) muscle (fish fed raw muscle, FR) or cooked grass carp muscle (fish fed cooked muscle, FC; 15 min ramp to ~100 °C followed by 2–3 min at ~100 °C). Locomotor activity and anxiety-like behavior were assessed using the open-field test and an annular light–dark preference assay, respectively. Flow-through respirometry further revealed a significantly lower standard metabolic rate (SMR) in FC fish than in FR fish, decreasing from 10.30 to 6.83, which represents a 33.7% reduction. Endocrine and biochemical analyses showed that cooking significantly decreased serum total triiodothyronine (T3) by 23.8%, whereas routine serum biochemical indices remained unchanged. In brain tissue, dopamine (DA) was significantly reduced by 7.2% in the FC group, and RT-qPCR analysis of dopamine-related genes further showed a significant downregulation of the rate-limiting synthesis gene th. These results indicate that cooking primarily downshifts the activity-energy axis in southern catfish and is accompanied by coordinated thyroid and dopaminergic changes. To our knowledge, this is the first integrated study to evaluate the behavioral, metabolic, and neuroendocrine effects of cooked feed in S. meridionalis, providing a short-term phenotypic baseline for assessing welfare-relevant feeding scenarios in aquaculture.

Skin pigmentation is a critical determinant of quality and market value in farmed fish, while environmental stressors such as hypoxia can induce oxidative stress and metabolic disorders, thereby threatening fish health and aquaculture sustainability. The present study investigated the effects of dietary lutein and zeaxanthin on skin pigmentation, hepatic lipid metabolism, and oxidative stress responses in yellow catfish (Pelteobagrus fulvidraco) through a 50-day feeding trial followed by an acute hypoxia challenge. Fish (initial body weight: 25.98 ± 0.03 g) were randomly assigned to three experimental diets: a basal control diet (Con), or the basal diet supplemented with 0.2% lutein (Lut) or 0.2% zeaxanthin (Zea). Although no significant differences in growth performance were observed among dietary groups, skin yellowness and total carotenoid deposition in both skin and liver were significantly elevated in the Lut group (P < 0.05), followed by the Zea group. Lipidomic profiling revealed that both lutein and zeaxanthin supplementation modulated multiple lipid classes, including glycerophospholipids (GP), glycerolipids (GL), sphingolipids (SP), sterols (ST), and fatty acids (FA) in liver and skin tissues (P < 0.05). Skin lutein content exhibited strong positive correlations with phosphatidylcholine (PC) levels (R=0.978, P < 0.01) and the expression of lipid transport-related genes cd36 (R=0.978) and scarb1 (R=0.977, P < 0.01). Under acute hypoxic stress, fish fed Lut or Zea diets displayed significantly higher plasma SOD activity and lower levels of glucose, lactic acid, and MDA compared to the control group (P < 0.05). Moreover, lutein supplementation specifically upregulated the expression of antioxidant and anti-apoptotic genes (nrf2, sod, gpx, bcl2) while downregulating pro-apoptotic genes (p53, casp3) in the liver (P < 0.05). In conclusion, dietary lutein plays a more prominent role than zeaxanthin in enhancing skin pigmentation and antioxidant defense in yellow catfish, and its functional efficacy is closely associated with lipid metabolism and carotenoid transport mechanisms.

Temperature is a crucial environmental factor for poikilothermic aquatic species and can affect their protein utilization. This study examined the impacts of temperature (optimal 27 degrees C vs. high 33 degrees C) and protein blends (formulated at 1:1:8:2, 1:1:6:4, and 1:1:4:6 ratios using Chlorella meal, Tenebrio molitor meal, Clostridium autoethanogenum protein, and cottonseed protein concentrate as fishmeal substitutes) on growth performance, health status, and gut microbiota of gibel carp. Healthy fish (3.45 +/- 0.03 g) were randomly distributed among 24 tanks (30 fish/tank), with each temperature condition assigned four experimental diets and each treatment replicated in three tanks for an 8-week feeding trial. High temperature (33 degrees C) enhanced feed intake and final body weight, but reduced feed efficiency (FE) and the apparent digestibility coefficients of crude protein and total essential amino acid. It also decreased intestinal superoxide dismutase, glutathione, and glutathione peroxidase activities, increased malondialdehyde content and elevated heat shock protein 70 (HSP70) and HSP90 levels. Moreover, it down-regulated il10 and tgf beta transcription and reduced villus height with lymphocyte infiltration. Furthermore, there was an enrichment in phyla Proteobacteria and Actinobacteriota and genera Mycobacterium, while beneficial Cetobacterium abundance was decreased. Compared to fishmeal, the protein blend in a 1:1:6:4 ratio improved FE and protein retention efficiency at 33 degrees C. Concurrently, this blend augmented the abundance of phyla Firmicutes and genera Clostridium_sensu_stricto_12. In summary, although elevated temperature enhanced growth via hyperphagia, it substantially compromised intestinal health and nutrient utilization. This adverse effect was mitigated through nutritional intervention with the optimized 1:1:6:4 protein blend formulation.

This study investigated the effects of dietary leucine on growth, lipid metabolism, and reproductive performance in female yellow catfish (Pelteobagrus fulvidraco) broodstock. Leucine deficiency significantly compromised growth and feed utilization (P < 0.05). Plasma aspartate aminotransferase activity was lowest, whereas albumin concentration was highest, in fish fed the diet containing 3.80% leucine. Although hepatic lipid deposition increased, plasma triglycerides declined with the increasing dietary leucine levels. Notably, the mesenteric fat index exhibited a significant linear decrease with increasing dietary leucine (3.18%–4.22%), suggesting a tissue-specific lipid-lowering effect conducive to reproduction. Consequently, dietary leucine supplementation significantly enhanced fertilization rates, hatching rates, and larval viability. Mechanistically, these improvements were attributed to the upregulation of ovarian steroidogenic genes (ar, lhr, and 3β-hsd) and elevated plasma follicle stimulating hormone (FSH) and estradiol (E2) levels, implicating the FSH-E2 axis. Crucially, the optimal leucine requirement for yellow catfish exhibited a hierarchical increase: 3.60% for fertilization, 3.88% for growth, and 4.02% for larval viability. This suggests higher maternal reserves are critical for supporting late-stage embryogenesis and offspring morphogenesis. Therefore, a dietary leucine level of 4.02% is recommended to simultaneously minimize mesenteric fat deposition and ensure superior growth performance, reproductive success and offspring quality in female yellow catfish.

Viral infections remain a challenge to aquaculture, resulting in severe economic losses and threatening fish health worldwide. As a key immunomodulatory and antiviral factor, interferon (IFN) plays a crucial role in regulating immune responses. We constructed a high-level expression strain of recombinant interferon (Rec-IFN) using Synechococcus sp. PCC 7002, which also served as a delivery system, and evaluated its efficacy as a dietary immunostimulant in gibel carp (Carassius gibelio) and zebrafish (Danio rerio). Analysis of the intestinal microbiome indicated that the Rec-IFN diet promoted beneficial bacteria such as Cetobacterium while reducing opportunistic pathogens including Aeromonas and Vibrio in gibel carp. Notably, after Cyprinid herpesvirus-2 (CyHV-2) infection, the Rec-IFN diet enhanced microbial connectivity, helping to preserve gut microbiota function. In zebrafish, the Rec-IFN diet increased species richness and evenness, while reducing opportunistic pathogens such as Vibrio. Transcriptomic analysis revealed specific activation of the Toll-like receptor signaling pathway and a reduction of immune overstimulation following infection in zebrafish. Our findings demonstrate that the Rec-IFN diet significantly enhanced the host IFN response and alleviated virus-induced damage to intestinal and immune organs, reduced viral load, and decreased mortality. This research offers a protective effect by reducing the severity of infections caused by both DNA virus (CyHV-2) and RNA virus (SVCV). It provides new insights into the application of Rec-IFN microalgae as an effective oral immunotherapeutic strategy for reducing losses from viral infections in aquaculture.

Stocking density and feed protein sources are critical in aquaculture. This study investigated their effects on growth, stress response, and protein utilization in gibel carp. Fishmeal served as the control diet (diet 1), while it was replaced by a blend of Tenebrio molitor meal, Chlorella meal, Clostridium autoethanogenum protein, and cottonseed protein concentrate in various ratios: 1:1:8:2 (diet 2), 1:1:6:4 (diet 3), and 1:1:4:6 (diet 4). Fish were raised at either a low stocking density (100 fish/cage, 20 fish/m3) or a high density (400 fish/cage, 80 fish/m3), with 6000 fish in total. The interaction of stocking density and diet affected growth and protein utilization. At a stocking density of 20 fish/m3, diet 2 effectively replaced fishmeal without compromising growth performance. At 80 fish/m3, only diet 3 achieved full fishmeal replacement without negative impacts on growth. High stocking density induced chronic stress, as seen by lower plasma glucose and higher muscle heat shock protein 70 and lactate levels. It also impaired intestinal function and muscle growth at the transcript level, reducing villus height and resulting in poorer growth performance. Diet 4 decreased trypsin and chymotrypsin activities, lowered villus height and the villus height/crypt depth ratio, and reduced plasma and muscle amino acid levels. It also downregulated genes involved in muscle protein synthesis, leading to reduced protein utilization. In conclusion, the optimal protein blend ratio was 1:1:8:2 ​at lower stocking densities and 1:1:6:4 ​at higher stocking densities, both of which achieved growth performance comparable to fishmeal. This density-specific protein blending strategy offers a scalable approach to formulating fishmeal-free feeds for intensive aquaculture systems without compromising productivity.

Atractylodes macrocephala polysaccharide (AMP) exhibits antioxidant, anti-inflammatory, and intestinal protective properties. However, its effective dietary supplementation level in aquaculture remains unclear. This study aimed to define the effective range and optimal supplementation level of dietary AMP in largemouth bass (Micropterus salmoides). Fish (initial weight 3.41 +/- 0.01 g) were fed diets containing 0, 100, 200, 400, 600, and 1200 mg/kg AMP for 10 weeks. Dietary AMP improved growth performance, with 400 mg/kg producing the most consistent enhancement in weight gain rate and feed utilization. AMP supplementation at 200 mg/kg enhanced antioxidant capacity and modulated the Nrf2/Keap1 pathway, while 100-600 mg/kg reduced apoptosis-related responses and improved intestinal morphology and barrier function. Correlation analysis further revealed that antioxidant capacity was positively associated with intestinal barrier integrity and growth performance, but negatively associated with oxidative stress and apoptosis-related indices, indicating coordinated physiological responses to dietary AMP supplementation. Overall, dietary AMP exerted beneficial effects on growth and health status in largemouth bass, and 400 mg/kg is suggested as an effective and practical supplementation level based on integrated physiological responses.

Fish exhibit limited efficiency in carbohydrate utilization, necessitating research to enhance their metabolic capacity for carbohydrates. Mitochondrial fatty acid beta-oxidation (FAO) inhibition might alter carbohydrate utilization and reduce protein consumption, thereby remodeling energy homeostasis. To clarify the energy allocation in gibel carp (Carassius gibelio var. CAS V) under impeding mitochondrial FAO, diets supplemented with or without the carnitine palmitoyltransferase 1 (Cpt1) inhibitor etomoxir (ETO; 0.25 g/kg) were fed to gibel carp for 8 weeks, followed by glucose tolerance tests (GTT). The results showed that mitochondrial FAO inhibition induced ectopic lipid deposition and upregulated peroxisomal FAO. Additionally, enhanced phosphorylation level of protein kinase B (Akt) protein indicated ameliorated insulin sensitivity. Concurrently, the upregulation of gk and glut4 and the downregulation of fbp evidenced the increased glucose utilization and led to the reduced glycogen accumulation. Furthermore, significantly changed metabolites (SCMs) related to amino acids were upregulated, and differentially expressed genes (DEGs) participating in amino acid biosynthesis were identified. These molecular changes and increased protein content in muscle pointed to a protein deposition in gibel carp. In conclusion, mitochondrial FAO inhibition remodeled energy homeostasis by compensatory upregulation of peroxisomal FAO and glucose utilization, ulteriorly realizing muscle protein deposition in gibel carp.

High-fat diets have been widely used in aquaculture because of their protein-sparing effect. However, high-fat diets have some negative effects on flesh quality in farmed fishes. This study investigated the potential of exercise to ameliorate the negative effects of a high-fat diet on the flesh quality of channel catfish (Ictarulus punctatus). A total of 120 channel catfish (54.58 ± 0.32 g) were randomly allocated to four treatments with triplicate tanks (10 fish per tank). Channel catfish were fed either a control diet (crude lipid = 6 %) or high-fat (HF) diet (crude lipid = 11 %) under two conditions: voluntary swimming (water velocity = 0.84 cm/s, 0 BL/s) and exercise (water velocity = 20.84 cm/s, 1 BL/s) for 58 days. We found that long-term intake of a HF diet adversely altered muscle composition and texture regardless of exercise, while impairing nutritional value and antioxidant capacity of voluntarily swum fish. However, the adverse effects observed with the HF diet on protein synthesis signaling (s6k1), essential amino acids, and total amino acids were attenuated with exercise. The HF diet promoted fasn expression and inhibited lipid catabolism (lpl and cpt1b) in the voluntarily swum fish only. Exercise reduced lipid accumulation in the muscle by inhibiting lipid synthesis-related gene expression (acaca and srebp1). Notably, exercise also inhibited fasn expression under the HF diet. These modulations were related to the activation of the AMPK/SIRT1/PGC-1α pathway. Moreover, exercise increased the levels of ARA, EPA, DHA, and n-3 PUFAs in muscle under the HF diet, thereby enhancing its nutritional value. Additionally, exercise increased muscle collagen content and improved muscle cellularity by upregulating the expression of genes related to myofiber development (myod1 and myhc). Under the HF diet, exercise also suppressed the expression of mstna and mstnb. These modulations ultimately enhanced flesh hardness and improved overall texture. Furthermore, exercise increased taste-active free amino acids and decreased off-flavors in fillets regardless of diet, while increasing aromatic flavor substances under the HF diet, thereby improving sensory qualities. Exercise also elevated muscle catalase levels and improved muscle antioxidant capacity under the HF diet. Our study suggests that exercise effectively alleviates the adverse effects induced by a HF diet on the flesh quality of channel catfish.

This study aimed to investigate the effects of dietary protein source (DPS) and extrusion temperature (ET) on the physical qualities of extruded grass carp feed and the growth performance, tissue composition, and gut microbiota of these animals. We used a 2 × 2 factorial experimental design, with DPSs consisting of mostly plant or fishmeal proteins extruded at 120 °C (DP1 and DA1 diets) or 140 °C (DP2 and DA2 diets) for grass carp. The growth trial was performed for 9 weeks, and the gut microbiota trial lasted 4 weeks. Compared with the fishmeal-based diets, the plant protein-based diets produced higher expansion ratios (P < 0.001). A high ET also improved the expansion ratio (P < 0.001) and significantly decreased the feed pellet bulk density (P < 0.001). The DP2 diet had the highest hardness and water solubility index and the lowest water absorption index. The DP1 diet exhibited the lowest protein and phosphorus apparent digestibility coefficients (ADCs). The ET significantly affected the ADCs for the plant protein-based diets, but not for the fishmeal-based diets. Grass carp fed the DP1 diet presented the lowest weight gain and specific growth ratio. The interactions between DPS and ET affected the final body weight (P = 0.030), protein efficiency ratio (P = 0.011), and feed efficiency (P = 0.016), and these indices were significantly greater in grass carp fed the DP2 diet than in those fed the DP1 diet. However, DPS and ET did not affect the concentrations of crude protein or amino acids in the dorsal muscle. Compared with grass carp fed plant-based diets, those fed fishmeal-based diets presented greater fat contents in the muscle (P = 0.011) and liver P = 0.037), and a greater hepatosomatic index (P = 0.003). The interaction of DPS and ET influenced the viscerosomatic index (VSI, P = 0.001), with the highest VSI found after feeding the DA2 diet. DPS (P = 0.001) but not ET (P = 0.172) significantly affected the gut microbial communities, although the plant protein-based diets with increased ET resulted in more differential taxa and greater differences in the abundances of the core microbiota in grass carp compared to the fishmeal-based diets. These results indicate that improving the ET of plant protein-based diets can alter the physical qualities of the diets, further affecting the gut microbiota, and enhancing the growth performance of grass carp. These findings reveal that higher ETs are needed for plant protein-based diets than for fishmeal-based diets, which is a valuable guideline for feed production.

High-plant protein diets can present certain limitations for the growth and health of aquaculture species. By incorporating essential amino acids into grass carp feed based on amino acid balance, this study investigated their role in alleviating the previously mentioned challenges. The control diet consisted of soybean meal, rapeseed meal, and cottonseed meal as the major protein sources. In contrast, the experimental diet was fortified with 0.21 % lysine, 0.32 % methionine, and 0.23 % threonine. A total of 300 grass carp (61.3 g) were randomly allocated into six net cages and fed with either the control or experimental diet for eight weeks. The results demonstrated that dietary amino acid supplementation improved weight gain rate, specific growth rate, and feed efficiency (P < 0.05). Moreover, it downregulated the mRNA expression of the TLR/MyD88/NF kappa B signaling pathway and pro-inflammatory cytokines (P < 0.05), mitigating intestinal inflammation. Regarding the intestinal microbiota, this treatment increased ACE and Chao indices, accompanied by an elevation in the abundance of Firmicutes and a concomitant reduction in Spirochaetota and Brevinema (P < 0.05). Furthermore, the diet with amino acid supplementation increased hepatic sm transcript levels and cholesterol contents (P < 0.05). It also stimulated the mRNA expression of the cyp7a1, leading to elevated levels of hepatic cholic acid, taurocholic acid, taurochenodeoxycholic acid, and glycochenodeoxycholic acid 3 sulfate disodium salt and increased intestinal bile acid concentrations (P < 0.05). In summary, the essential amino acid supplementation reshaped the bile acid cycle of the host by promoting hepatic cholesterol and bile acid synthesis and influencing the composition of the gut microbiota, alleviated intestinal inflammation, and improved the growth of grass carp. The findings revealed that optimizing the amino acid balance in feed formulations can improve fish growth performance and health while lowering production costs, thereby supporting the sustainable advancement of the aquaculture sector.

This study evaluated the effects of dietary carbohydrate levels on glycolipid metabolism and liver health of channel catfish. Six isonitrogenous and isolipidic diets with corn starch contents of 10 % (C10), 15 % (C15), 20 % (C20), 25 % (C25), 30 % (C30) and 35 % (C35) were set up. After 8-week feeding trial, there was no significant difference in the growth performance of all groups (P > 0.05). The study showed that C30 and C35 groups significantly increased plasma glucose levels, activated the expression of glycolysis-related genes (gk, hk, pklr, pfk) and mitochondrial oxidative phosphorylation related genes (ndufa1, sdhb, sdha, cytb-c1, cox, atp5fa1, atp5f1b), and repressed the expression of gluconeogenesis-related genes (pc, fbp, pepck, g6p) in the channel catfish (P < 0.05). The upregulation of glycogen synthesis-related genes (ppp1r3g, ppp1r3c, ppp1r3b, gys, gnl, ugp2a, ugp2b) contributed to a significant increase in hepatic glycogen content. In addition, C30 and C35 groups significantly increased the expression of pentose phosphate pathway related genes (g6pd, 6gpd), while C10 to C25 groups glucose metabolism-related pathways did not exhibit significant differences. Hepatic triglyceride and cholesterol results showed that C30 and C35 groups induced excessive lipogenesis, activated the expression of lipogenesis-related genes (acc, acly, vldlr) and cholesterol synthesis-related genes (srebf2, hmgcr, sqle). In C30 and C35 groups also increased the hepatic ALT, AST and MDA levels, activated the expression of injury-related genes (a-sma, tgf-β), inflammation-related genes (tnf-α, il-1β, il-6) and apoptosis-related genes (baxb, caspase-3, caspase −10) (P < 0.05). C35 group significantly further increased the expression levels of stress genes such as hamp, hsp70 and hsp90 (P < 0.05), while there were no significant differences in the levels of lactate and cortisol in all groups (P > 0.05). In conclusion, our results suggest that dietary carbohydrate levels less than 30 % will not impair the health and growth performance of the channel catfish.

High carbohydrate diet (HCD) has been shown to disrupt hepatic glycolipid metabolism and contribute to the development of metabolic dysfunction-associated steatotic liver disease (MASLD). However, effective therapeutic strategies targeting the underlying pathological mechanisms remain limited. Here, we designed a series of feeding experiments to evaluate the effects of dietary c-SRC inhibitor (UM-164) on glycolipid metabolism and liver health in channel catfish (Ictalurus punctatus) fed HCD. The experimental design consisted of three isonitrogenous and isolipidic diets: CON (18 % corn starch), HCD (36 % corn starch), and HCS (36 % corn starch; 20 mg/kg UM-164). Juvenile channel catfish (7.63 +/- 0.02 g) were fed with these diets for 8 weeks. Our results revealed that the HCS treatment mitigated the HCD-induced increases in hyperglycemia, hyperlipidemia and glycosylated hemoglobin (GHb). HCS reduced the HCD-induced upregulation of pentose phosphate pathway (PPP)-related genes (c-src, g6pd and 6pgd), NADPH levels and glycolytic genes (hk1, gk, pfkla, pfklb and pk). HCS reduced liver glycogen content by inhibiting the expression of PPP1R3G. HCS attenuated the HCD-induced activation of mTOR, leading to reduced expression of key lipid synthesis factors (SREBPs), as confirmed in vivo and vitro experiments. HCD resulted in a significant elevation of liver health indicators (ALT and AST), and UM-164 alleviated the HCD-induced liver damage. In conclusion, UM-164 reduced HCD-induced hepatic lipid accumulation by inhibiting PPP and mTOR-SREBPs signaling, thereby improving liver health. These findings suggest that UM-164 is a promising therapeutic agent for protecting liver health and may provide a viable basis for the treatment of MASLD.

In order to investigate the effect of sodium bicarbonate(NaHCO3)on intestinal damage in largemouth bass(Micropterus salmoides)under chronic high-temperature stress,juvenile largemouth bass(20.26±0.08)g were fed diets with or without sodium bicarbonate(NaHCO3,5 g/kg)for 8 weeks.The results showed that there was no significant difference in the specific growth rate in the NaHCO3 group compared to the control group at chronic high temperatures.However,the NaHCO3 group exhibited significantly improved feed efficiency,protein deposition rate,and protein effi-ciency,along with a marked increase in intestinal amylase and trypsin activities.The addition of NaHCO3 also signifi-cantly enhanced the intestinal total antioxidant capacity(T-AOC),catalase(CAT),superoxide dismutase(SOD),and glutathione peroxidase(GPx)activities.Furthermore,NaHCO3 up-regulated the expression of cat and gpx1a genes and down-regulated the gene expression of keap1.Meanwhile,the expressions of pro-inflammatory cytokines(il-1β,tnfα,and il15)were significantly down-regulated in the group,while the expression of anti-inflammatory cytokine il10 was up-regulated.In addition,the expression of hsp90,hsp70,and hsp60 genes in the intestines of largemouth bass in the NaHCO3 group was significantly lower than that in the control group.Histologic analysis of the intestinal tract showed that high-temperature stress induced intestinal damage in largemouth bass,and the addition of NaHCO3 significantly improved the intestinal tissue morphology and up-regulated the expression of intestinal zo1,jam,occludin,and muc2.In conclusion,the addition of 5 g/kg NaHCO3 to the feed effectively alleviated chronic high-temperature stress-induced intestinal damage in largemouth bass by improving intestinal antioxidant capacity,intestinal inflammation,and intesti-nal barrier function.These findings may provide a new perspective to improve the intestinal health of fish under high-temperature stress.

This study aimed to evaluate the effects of dietary carbohydrate and protein levels on growth performance, nutrient metabolism, liver function and flesh quality of channel catfish (Ictarulus punctatus). Four experimental diets were designed containing 20 % or 32 % carbohydrate with 32 % or 36 % protein, respectively (C20P32, C20P36, C32P32 and C32P36) and fed to triplicated groups of channel catfish (initial body weight: 60.88 +/- 0.42 g) for 8 weeks. A two-way ANOVA revealed significant interactions between dietary carbohydrate and protein levels, influencing growth performance, VSI, LRE, body composition (lipid, moisture and ash), plasma metabolites (T-CHO, TG, HDL-C and LDL-C), liver T-CHO level and g6pase mRNA expression. Higher dietary carbohydrate increased FE, IPF, CF and PER, whereas higher protein level reduced PRE and PER. High carbohydrate intake promoted hepatic glucose transport (glut2), glycolysis (gk, pfkl, pkl), glycogenesis (gys2), glycogenolysis (pygl) and lipogenesis (TG content, Oil Red O area, expression of acaca, srebp1, fasn and scd). Concurrently, it suppressed lipolysis (lpl, perilipin, cpt-1a, aco and ppar alpha), resulting in increased glycogen and lipid accumulation in the liver. Moreover, high carbohydrate decreased AST activities and up-regulated the expression of protein synthesis genes (mtor, s6k1 and s6) in liver. Notably, there were no significant differences in plasma ALT, AST and AKP levels, liver ROS and MDA contents as well as the expressions levels of liver inflammatory cytokines (tgf beta, tnf alpha, il6 and il1 beta) among the groups. In terms of white muscle, dietary carbohydrate and protein levels interacted to affect lipid content, the expression levels of genes involved in lipid and glycogen metabolism, mrf4 expression level, fatty acid profiles (EPA, DHA, n-3 PUFA and PUFA) and texture properties (flexibility, adhesiveness and stringiness). Furthermore, high carbohydrate increased muscle glycogen, lactate and LDH contents, while decreased water holding capacity and myf5 expression level in muscle. Higher protein level enhanced the ratio of n-3/n-6 PUFA, myog expression level and fracturability, but reduced toughness in muscle. In conclusion, the addition of carbohydrates to the diet of channel catfish had a protein-sparing effect. Dietary carbohydrate and protein levels didn't affect liver function, while induced several modifications on flesh quality in channel catfish.

This study was carried out to search for the protein requirement of a new strain of preponderant amphitriploid Carassius clone, which integrated genomes partly from white crucian carp (C. auratus cuvieri). Seven groups of fish (body weight: 9.73 ± 0.03 g) were fed with seven isolipidic and isocarbohydrate diets containing 21.38%, 25.82%, 27.94%, 31.36%, 34.23%, 37.87%, and 40.70% crude protein (P21, P24, P27, P30, P33, P36, and P39), respectively. After 8-week feeding, weight gain rate (WGR) and specific growth rate (SGR) were lower in the P30 group than those in the P39 group, but no difference was found in final body weight (FBW), survival, condition factor (CF), or hepatosomatic index (HSI) between different groups. Increased dietary protein decreased feeding rate (FR) and viscerosomatic index (VSI) while improved feed efficiency (FE). Decreased protein retention efficiency (PRE) and improved activity of liver alanine aminotransferase (ALT) and content of plasma ammonia suggested intensified fish amino acid catabolism in high dietary protein groups. The dietary protein requirement of the new Carassius clone was as low as 21.38% for growth. The optimal dietary protein for high FE was 39.62% and should be less than 30.56% to maintain the maximum protein retention. High dietary protein might be harmful to the fish due to the increased contents of liver malondialdehyde (MDA) and plasma cortisol. Dietary protein level altered fish body and muscle flavor substance composition. Low dietary protein could obtain high muscle fatty acid, free amino acid, and lipid accumulation, including whole body and muscle crude lipid, plasma total triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-c), and low-density lipoprotein cholesterol (LDL-c). Therefore, the recommended dietary protein for this new Carassius clone juvenile should be 21.38%-30.56%.