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.

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.

The aim of this study was to investigate the dietary zinc (Zn, from ZnSO₄·H₂O) requirement of subadult red swamp crayfish (Procambarus clarkii) through a feeding trial followed by the analysis of growth performance, immune status, antioxidant activity, and lipid profile. Red swamp crayfish were fed six isonitrogenous and isocaloric diets, containing different Zn content of 45.58, 50.33, 58.82, 68.29, 94.11, and 142.72 mg/kg for 9 weeks. The results showed that, compared with the control group, when dietary Zn content reached 68.29 mg/kg, red swamp crayfish exhibited a significant increase in final body weight (FBW), feeding rate (FR), weight gain rate (WGR), and specific growth rate (SGR), along with a significant reduction in feed conversion ratio (FCR) (P < 0.05). As dietary Zn levels rose, Zn content in whole crayfish and crayfish shells increased first and then reached a plateau when the dietary Zn content reached 94.11 mg/kg (P < 0.05). In contrast, the content of iron, copper, and manganese in whole crayfish and crayfish shell, as well as iron content in muscle, initially decreased and then stabilized with increasing dietary Zn levels (P < 0.05). Compared with the control group, a dietary Zn content of 68.29 mg/kg significantly enhanced serum immune capacity and hepatopancreatic antioxidant activities (P < 0.05), significantly improved hepatocyte health and reduced lipid accumulation (P < 0.05), significantly downregulated the expression of fasn, acc, acsl, and srebp in the hepatopancreas (P < 0.05), and significantly upregulated the expression of cpt2 and acox1 in the hepatopancreas (P < 0.05). Based on the broken-line analysis of SGR, FCR, and immune enzyme AKP activity, the optimal dietary Zn requirement for subadult red swamp crayfish was assessed to be 66.07, 65.60, and 66.13 mg/kg, respectively, using ZnSO₄·H₂O as the Zn source. For practical feed formulations, a Zn requirement of 66 mg/kg diet is recommended to support optimal growth and health for subadult red swamp crayfish.

To evaluate the effects of soybean meal (SBM) fermented with Lactobacillus rhamnosus GG (LGG) or Lactobacillus reuteri (LR) on the growth and intestinal health of hybrid yellow catfish, the SBM was first mixed with sterile water at a ratio of 7:3, and then combined with L. rhamnosus GG or L. reuteri at a ratio of 97:3 for 72 h of anaerobic fermentation. Subsequently, three diets were formulated: the SBM diet (containing 33.75% SBM), the LGG-FS diet (containing 33.75% LGG-fermented SBM) and the LR-FS diet (containing 33.75% LR-fermented SBM). These diets were used to feed hybrid yellow catfish (initial body weight: 5.57 +/- 0.01 g) for 42 days. The results demonstrated that the nutritional quality of SBM was markedly enhanced by L. rhamnosus GG or L. reuteri fermentation as reflected in an increase of 2- or 3- fold in lactic acid (LAC), an elevated ratio of essential amino acid (REAA), and the increases of 8.91% or 14.85% in the essential amino acid index (EAAI), respectively. Moreover, a reduction of 23.2% in pH and a reduction of 16.30% in beta-conglycinin were observed in L. rhamnosus GG-fermented SBM. Meanwhile, a reduction of 29.1% in pH, a decrease of 58.08% glycinin, and a decrease of 33.92% in beta-conglycinin were observed in L. reuteri fermented SBM. Compared with fish fed SBM diet, hybrid yellow catfish fed with LGG-FS diet or LR-FS diet exhibited improved intestinal histomorphology and barrier function, and the reduced intestinal inflammation. In LR-FS group, the final body weight (FBW), weight gain rate (WGR) and specific growth rate (SGR) were even significantly higher, and feed conversion ratio (FCR) was significantly decreased (P < 0.05). Compared with SBM group, Shannon index was significantly increased and Simpson index was significantly decreased in LGG-FS group (P < 0.05). Principal coordinates analysis (PCOA) revealed a clear separation of microbial communities between the LR-FS and the SBM groups. At the phylum level, the LR-FS group exhibited an increased abundance of Firmicutes, and a decreased abundance of Fusobacteriota and Proteobacteria (P < 0.05). At the genus level, the abundance of Candidatus_arthromitus was significantly higher and the abundance of Cetobacterium was significantly lower in LR-FS group (P < 0.05). The correlation analysis exhibited that Candidatus_arthromitus negatively associated with indices of intestinal inflammation and positively correlated with indices of antioxidant capacity and intestinal barrier functions, while Cetobacterium showed an opposite correlation with these indices. Overall, the results suggest that L. reuteri rather than L. rhamnosus GG, is a more promising probiotic for enhancing growth performance and intestinal health in hybrid yellow catfish with SBM-induced enteritis (SBMIE).

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.

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.

This experiment investigated the effects of different levels of Vitamin E addition on the growth, immunity, and ovarian development of red swamp crayfish (Procambarus clarkii). A total of 720 crayfish (8.14 +/- 0.05 g) were selected and divided into six groups, with four replicates per treatment. The experimental diets with Vitamin E addition amounts of 0 mg/kg (E0), 50 mg/kg (E1), 100 mg/kg (E2), 200 mg/kg (E3), 400 mg/kg (E4), and 1000 mg/kg (E5) were fed to crayfish for 56 days. Dietary supplementation with 100-200 mg/kg Vitamin E significantly improved weight gain rate (WGR) and specific growth rate compared with the diet without Vitamin E (0 mg/kg) (P < 0.05). Lipase and amylase activities in the hepatopancreas and intestine reached their peak in the 200 mg/kg group. Histological observations indicated more intact and better-organized hepatopancreas and intestinal structures in the 100-200 mg/kg groups. Serum lipid profiles were improved in the 200 mg/kg group, characterized by lower triglyceride and low-density lipoprotein cholesterol levels, and higher high-density lipoprotein cholesterol levels (P < 0.05). Supplementation with 200 mg/kg Vitamin E significantly increased serum acid phosphatase and lysozyme activities, and decreased alanine aminotransferase activity compared with the 0 mg/kg group (P < 0.05). In terms of lipid metabolism, the 200 mg/kg Vitamin E exhibited upregulated expression of lipid synthesis-related genes (fas, srebp1, acsbg, acc2) and lipid transport-related genes (fabp, fatp), and downregulated expression of lipid decomposition-related genes (cpt-1, atgl, aco, pla2) (P < 0.05). Dietary supplementation of 200 mg/kg Vitamin E upregulated and downregulated the expression of molting-promoting (mtor and s6k1) genes and -inhibiting (4ebp1 and mih) genes, respectively. Regarding ovarian development, adding 200 mg/kg of Vitamin E can upregulate the mRNA levels of pka, fox l2, vg, cdc2, and cyclin b. In conclusion, dietary vitamin E exerts a dose-dependent effect on the growth performance and major physiological parameters of P. clarkii. Based on the WGR and feed conversion ratio, a supplementation level of 128.3771-142.5556 mg/kg Vitamin E is recommended to meet its growth and physiological requirements.

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.

The effects of berberine (BBR) on intestinal health suffering from soybean meal (SBM)-induced enteritis (SBMIE) in hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × Pelteobagrus vachelli ♂) were investigated in this study, focusing specifically on oxidant-antioxidant capacity, intestinal morphology, microbiota homeostasis and tryptophan catabolites. A total of 270 individuals with the initial body weight (IBW) of 23.27 ± 0.60 g were randomly divided into 9 tanks at the density of 30 fish per tank. Three diets, the SBM diet (75% of fish meal substituted by SBM, SBM), BBR1 (75 mg/kg BBR was added to the SBM diet, BBR1) and BBR2 diet (150 mg/kg BBR was added to the SBM diet, BBR2), were used to feed fish for 42 d. The results indicated that the final body weight (FBW), weight gain rate (WGR) and specific growth rate (SGR) were all significantly increased in BBR2 group compared with SBM group (P < 0.05). Intestinal barrier proteins and genes (ZO-1 and occludin) expression (P < 0.05) and intestinal interleukin-10 (IL-10) content (P = 0.001) were all greatly improved with BBR administration, especially in the BBR2 group. The apoptosis related genes (caspase 3 and caspase 9) (P < 0.05) of intestinal epithelium cells were also significantly reduced by dietary BBR compared with SBM group. Comparative analysis of intestinal microbial composition and tryptophan catabolites between the SBM group and BBR2 group revealed that BBR significantly ameliorated the imbalance of intestinal microbiota and improved the intestinal tryptophan catabolites, especially reflected in the relative abundance of Romboutsia and the levels of L-5-hydroxytryptophan (L-5-HTP), indole-3-acetic acid (IAA) and kynurenine (KYN) in intestinal contents (P < 0.05). As a result, the aryl hydrocarbon receptor (AhR) signaling was then activated. Correlation analyses showed that the relative abundance of Romboutsia was positively correlated with IAA and KYN levels in the intestinal contents (P < 0.05), and negatively correlated with interleukin-1 beta (IL-1β) and interleukin-6 (IL-6) levels in hindgut (P < 0.01). The levels of L-5-HTP, IAA, and KYN in intestinal contents were positively correlated with key factors of hindgut AhR signaling pathway, tight junctions (TJs) and anti-inflammatory cytokines (P < 0.05). Kyoto Encyclopedia of Genes and Genomes (KEGG) functional prediction results showed that the intestinal microbial functions were mainly enriched in metabolic pathways, including amino acid metabolism, carbohydrate metabolism, and metabolism of cofactors and vitamins. In conclusion, BBR ameliorated SBMIE in hybrid yellow catfish by reducing oxidative stress, enhancing antioxidant and anti-inflammatory capacity, alleviating intestinal pathological damage and microbial dysbiosis. The microbiota-tryptophan catabolite-AhR axis may play an essential role in this protective process.

The relatively low edible muscle yield and inconsistent flesh texture of red swamp crayfish limit its commercial value and highlight the need for effective nutritional interventions. Although L-carnosine has shown beneficial effects on muscle growth and quality in vertebrates, its nutritional functions and underlying mechanisms in crustaceans remain unclear. This study aimed to evaluate the effects of dietary L-carnosine on growth performance and muscle quality in red swamp crayfish (Procambarus clarkii). A total of 324 red swamp crayfish, with an initial body weight of 6.19 ± 0.03 g, were randomly divided into 6 groups of three replicates and 54 crayfish per group (18 crayfish per replicate). Six experimental diets containing graded levels of L-carnosine (3.35, 59.28, 106.84, 222.20, 452.93, and 821.16 mg/kg) were fed for 8 weeks. Regression analysis revealed dose-dependent responses in multiple parameters. Weight gain rate, specific growth rate, protein efficiency ratio, protein deposition rate, muscle percentage, whole-body and muscle crude protein content, muscle textural properties (hardness and chewiness), hydroxyproline levels (alkaline-insoluble and total), myofiber density, small myofiber proportion (<50 μm), and total amino acid content exhibited quadratic trends (P < 0.05), with peak values observed in the 452.93 mg/kg group. Conversely, feed conversion ratio and large myofiber proportion (>70 μm) showed significant quadratic decreases (P < 0.05), reaching their lowest values at 452.93 mg/kg. Transcriptional analysis demonstrated that, compared with the 3.35 mg/kg L-carnosine group, the 452.93 mg/kg L-carnosine group significantly regulated genes involved in several key pathways: mTORC1 signaling (igf-1, pi3k, akt, tor, s6k1, and 4ebp1), eIF2B-eIF2 signaling (eif2a), ubiquitin-proteasome system (ub, psma2, psmc1, and murf1), autophagy-lysosomal system (atg16l1, atg5, beclin1, and atg12), TGFβ/Smads pathway (TGF-β1, smad6, smad3, smad4, and colla1), and myogenic regulators (mef2a, mef2b, and mstn) (P < 0.05). These molecular modulations were consistent with observed phenotypic improvements. Overall, the findings demonstrated that a dietary L-carnosine level of 458.06 to 500.00 mg/kg, as determined by quadratic regression analysis, significantly enhances growth performance, feed utilization, muscle hardness and chewiness, and nutritive value in red swamp crayfish.

To evaluate the impacts of dietary supplementation with creatine on growth performance and muscle quality in red swamp crayfish (Procambarus clarkii) (5.86 +/- 0.06 g). A total of 324 red swamp crayfish were randomly divided into 6 groups (54 crayfish per group), with three replicates per group (18 crayfish per replicate). The crayfish were fed all-plant-protein diets with six creatine levels (0, 2.50, 5.00, 10.00, 15.00, and 20.00 g/kg) for eight weeks. Our findings revealed that the weight gain rate (WGR), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), protein deposition ratio (PDR), crude protein content of muscle and whole body, hardness, chewability, total hydroxyproline content, proportion of myofibres < 40 mu m in diameter and density of myofibres all exhibited a remarkable quadratic polynomial pattern with the increase of dietary creatine supplementation (P < 0.05). Notably, compared to the control group, 5.00 g/kg creatine supplementation significantly reduced the FCR, while increasing all other indicators mentioned above (P < 0.05). Flesh percentage (FC), and the content of total essential amino acids and total amino acids displayed obvious linear and quadratic polynomial trends with increasing dietary creatine addition, and all these parameters were markedly higher in the 5.00 g/kg group compared to the control (P < 0.05). Furthermore, compared to the control group, 5.00 g/kg creatine significantly up-regulated the mRNA abundances of the key genes participating in protein synthesis (igf-1, pi3k, akt and tor), muscle collagen synthesis (tgf-beta 1, smad6, smad3, smad4 and col1a1) and muscle quality (mef2a and mef2b), while significantly down-regulated the mRNA expression of ubiquitin-proteasome system (ub, psma2, psmc1 and murf1) and autophagy-lysosome system (atg5, beclin1, atg12 and atg16l1) (P < 0.05). In conclusion, dietary creatine addition improved feed utilization, enhanced growth performance, promoted protein deposition and muscle growth of crayfish. Broken-line regression model analysis between WGR, SGR, FC, FCR and dietary creatine levels revealed an optimal creatine range of 4.29-5.66 g/kg.

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.

Current methods for the determination of ovarian maturation in fish have shortcomings. They are often time-consuming, inaccurate, and fish are sacrificed during the procedure. A novel noninvasive and accurate method to assess ovarian maturation can be to use magnetic resonance imaging (MRI). Long scanning time is a limitation for use in fish. A clinical MRI with a new sequence employing a shorter scanning time may be more feasible for the assessment of ovarian maturation in female fish. The aim of this study was to investigate ovarian maturation in Channa argus by clinical MRI with the three-dimensional fast spin echo Cube-flex (3D-FSE-Cube-Flex) T2WI sequence, compared with two traditional sequences. The results demonstrated that compared with two traditional sequences, the 3D-FSE-Cube-Flex T2WI sequence greatly reduced scanning time (only requiring 140 s per fish) without reducing the scanning quality. A significant correlation (R-2 = 0.985, p < 0.001, N = 112) was found between the percentage volume of the ovary measured by MRI and the gonadosomatic index (GSI). Besides, ovarian maturation MRI images at different development stages were captured. These findings suggest that clinical MRI with the 3D-FSE-Cube-Flex T2WI sequence is a rapid, accurate, and noninvasive method for assessing ovarian maturation, with great potential applications in sustainable aquaculture.

Feed nutrients are crucial in shaping the gut microbial community, especially for complex interactions. While much research focused on the impacts of dietary protein levels, exploration of protein sources remains insufficient. Accordingly, this study specifically investigated the effects of four protein sources [Clostridium autoethanolicum protein (CAP), cottonseed protein concentrate (CPC), Chlorella vulgaris meal (CVP), and Tenebrio molitor meal (TM)] replacing dietary soybean meal on microbial co-occurrence networks and key metabolic taxa. A 56-day feeding trial involved 1500 grass carp (20.00 g) fed five experimental diets, each incorporating one of the experimental protein sources. Results revealed that CPC and CVP diets improved the weight gain and specific growth rate, with the CPC group demonstrating the highest biomass gain and the CVP group exhibiting the best feed conversion ratio. Findings further indicated that SM-free diets enhanced intestinal immunity and barrier function while negatively impacting microbial diversity. Additional profiling revealed that each treatment exhibited distinct abundance profiles and unique species, with Firmicutes, Bacteroidota, and Proteobacteria as the dominant phyla and key genera such as Bacteroides, Erysipelatoclostridium, and Cetobacterium. Stochastic mechanisms drove the community assembly process, and prolonged SM-free diets led to simplified networks with increased generalists and specialists. Functional gene analysis highlighted roles in amino acid, carbohydrate, and lipid metabolism, underscoring the impact of protein sources on aquatic microbial communities and host-microbiome interactions. Overall, the study suggests the potential suitability of several protein sources as soybean meal substitutes, emphasizing the importance of further investigation into optimal inclusion levels for diverse proteins.

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 focuses on the effects of dietary vitamin A on growth performance, immunity, molting, lipid metabolism, and ovarian development of red swamp crayfish (Procambarus clarkii). Six experimental diets with vitamin A levels of 0 IU/kg (A0), 3000 IU/kg (A1), 9000 IU/kg (A2), 27000 IU/kg (A3), 81000 IU/kg (A4), and 243000 IU/kg (A5) were feed to P. clarkii (initial weight: 8.74 ± 0.05 g) for 8 weeks. The results showed that adding 27000 IU/kg of vitamin A to the feed can increase the weight gain rate (WGR) and specific growth rate of P. clarkii, reduce the feed conversion ratio (FCR), and hepatosomatic index (P < 0.05). It can enhance the digestive capacity of the hepatopancreas and intestine of P. clarkii. Supplementation with 27000 IU/kg of vitamin A activated the MIH regulatory mechanism and mTOR signaling pathway by upregulating the mRNA expression of EcR, RXR, mTOR, S6K1, E75 and Chitinase (P < 0.05), and downregulating the mRNA expression levels of MIH and 4EBP1 (P < 0.05). Compared with the A0 group, the addition of 27000 IU/kg vitamin A significantly enhanced the immunity and antioxidant capacity of P. clarkii. Dietary vitamin A (27000 IU/kg) downregulated the mRNA levels of myd88, NF-κB p105, mapk7 and tnf in the intestine (P < 0.05), and upregulated the mRNA expression of tgf-β (P < 0.05), thereby activating the MAPK/NF-κB signaling pathway in P. clarkii. In terms of lipid metabolism, the addition of 27000 IU/kg vitamin A reduced the lipid content, upregulated the mRNA expression of genes related to lipid synthesis (fas, srebp1, acsbg, acc2) and lipid transport (fabp, fatp) (P < 0.05), and downregulated the mRNA levels of genes related to lipid decomposition (cpt-1, atgl, aco, pla2) (P < 0.05). The accumulation of lipid in the hepatopancreas was decreased in the A3 group. In terms of ovarian development, 27000 IU/kg of vitamin A promoted the development of ovaries by upregulating the mRNA expression of Vg, PKA, CyclinB, cdc2 and fox L2 (P < 0.05), and activating the ECR/RXR signaling pathway to promote the production of yolk. In conclusion, based on the evaluation indicators of WGR and FCR, adding 14491.48-15990.83 IU/kg of vitamin A to the feed of P. clarkii for the growth and physiological needs was recommended.