The effect of dietary nutrients on novel farm species has always garnered wide research and economic interest. Chinese perch, an economically important carnivorous fish, accepts an artificial diet after taming, so it is essential to evaluate and optimize the nutritional and metabolic demands of this species. However, little is known about the effect of an artificial diet on the growth and metabolism of Chinese perch. Therefore, the present study evaluated the growth and metabolic responses of Chinese perch to experimental diets with different dietary protein/energy (P/E) ratios. Five isoenergetic diets (18 kJ/g) with graded levels of P/E ratios of 30.58, 33.22, 35.90, 38.6, and 41.35 mg/kJ (named A, B, C, D, and E) were formulated. A total of 225 Chinese perch (64.89 ± 0.28 g) were divided into five groups (triplicate tanks for each group), distributed into 15 (350 L) fiberglass tanks, and fed twice a day at 4% of fish wet body weight with the respective P/E ratio diets for 10 weeks. Compared with the other groups, Chinese perch in Group C showed significantly improved growth performance, weight gain (WG), specific growth rate (SGR), viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat (IPF), feed utilization, feed intake (FI), feed conversion ratio (FCR), protein efficiency ratio (PER), protein retention efficiency (PRE), energy retention efficiency (ERE), and feed efficiency (FE) as well as whole-body, muscle, and liver composition. Chinese perch in Group A, on the other hand, had the lowest growth performance, feed utilization, and body composition compared with the other groups. The activities of nitrogen metabolism-related enzymes (alanine aminotransferase (ALT), aspartate aminotransferase (AST) glutamate dehydrogenase (GDH), and adenosine 5′-monophosphate deaminase (AMPD)) as well as the mRNA expression of the GDH and AMPD genes were significantly lower than those in the other groups. Similarly, the expression of NPY and AgRp were significantly higher in Group C compared with the other groups. However, the gene expression of CART and POMC was not affected by the dietary P/E ratios. In Group A, the expression of mTOR, S6K, and 4EBP1 was significantly lower and that of AMPK, LKB1, and eEF2 was significantly higher when compared with the other groups. Biochemical analysis of blood showed that ALT, AST, total protein (TP), alkaline phosphatase (ALP), glucose (GLU), blood urea nitrogen (BUN), and triglyceride (TG) levels were also affected by the dietary P/E ratio. From our results, we concluded that Chinese perch growth performance and nutrient metabolism were significantly affected by the P/E ratio of the artificial diet. Second-order polynomial regression analysis revealed that Chinese perch growth performance was optimal at a P/E ratio of 37.98 in the artificial diet.

The growing demand for sustainable aquaculture has intensified research on probiotics as antibiotic alternatives. This study aims to evaluate the effects of three probiotic supplements—1 × 10¹⁰ CFU/g of Bacillus subtilis (BS), Clostridium butyricum (CB), or Enterococcus faecalis (EF)—on growth performance, antioxidant capacity, intestinal structure, and gut microbiota in grass carp (Ctenopharyngodon idella; initial body weight: 42.52 ± 4.17 g) for 28 d. Compared to the non-supplemented (NC) control group, all probiotic-supplemented groups significantly enhanced final body weight, weight gain rate, specific growth rate, and crude protein content, and reduced feed conversion ratio (p < 0.05). Probiotic supplementation upregulated the intestinal ctrb1 gene expression and increased villus length. Serum superoxide dismutase (SOD) and catalase activity were elevated in the BS group, whereas only SOD was increased in the CB group (p < 0.05). Gut microbiota analysis revealed reduced Proteobacteria abundance in all probiotic-supplemented groups. Compared with the NC group, the BS group enriched Bacteroidetes and Prevotella_7, while the CB group promoted the abundance of Actinobacteria, Lactobacillus, and Clostridium_sensu_stricto_1. The EF group increased the abundance of Fusobacteria, Cetobacterium, and Bacteroides (p < 0.05). These findings demonstrate that dietary supplementation with probiotics enhances growth performance by modulating antioxidant responses, intestinal morphology, and microbial community balance.

Chinese perch (Siniperca chuatsi), an economically important freshwater fish in China, faces ammonia nitrogen stress under high-density aquaculture. This study investigated chronic ammonia nitrogen exposure effects on juvenile fish (95 ± 5 g) to establish safe concentration. Acute toxicity tests revealed a 96 h-LC₅₀ of 12.91 mg/L ammonia nitrogen, with a safe concentration of 1.29 mg/L ammonia nitrogen (non-ionic ammonia: 0.097 mg/L). In 28-day chronic experiments with ammonia nitrogen levels at 0, 0.61, 1.29, and 2.58 mg/L, ammonia nitrogen induced hepatic oxidative stress, with total superoxide dismutase, catalase, and glutathione peroxidase activities and malondialdehyde content increasing proportionally to ammonia nitrogen concentration initially but declining over time. Concurrently, gill Na⁺-K⁺-ATPase activity was significantly suppressed, while the gene expression of ammonia transporters (rhag, rhbg, and rhcg) exhibited ammonia nitrogen concentration-dependent upregulation, inversely correlated with the exposure duration. Histological gill damage intensified at higher concentrations. Hepatic ammonia detoxification enzymes activities (asparagine synthase, glutamine synthetase, and glutamate dehydrogenase) and glutamine accumulation increased with ammonia nitrogen levels, aligning with gene expression trends, though enzyme activity diminished over time. Serum alanine aminotransferase and aspartate aminotransferase activities and their gene expressions rose with ammonia nitrogen levels, while total protein declined. These findings demonstrate that chronic ammonia nitrogen stress disrupts antioxidant capacity, osmoregulation, and nitrogen metabolism, compelling Chinese perch to mitigate toxicity via glutamine synthesis. To ensure sustainable aquaculture, ammonia nitrogen levels should remain below 1.29 mg/L under adequate dissolved oxygen conditions.

This study aimed to evaluate the effects of dietary supplementation with sodium butyrate (SB) in different forms on the growth performance, antioxidant capacity, immune response, and intestinal health of largemouth bass (Micropterus salmoides). Five diets were formulated: a basal diet (SB0), diets with 1000 (ESB1), 1500 (ESB2), and 2000 mg/kg encapsulated SB (ESB3), and a diet with 2000 mg/kg raw powder sodium butyrate (RSB, non-encapsulated). After 49 days of feeding trials, the ESB2 group exhibited significantly higher weight gain and specific growth rates and a lower feed coefficient than those of the SB0 group (p < 0.05). Compared with the SB0 group, proximal intestinal villus length and width were significantly increased in the ESB1, ESB2, and ESB3 groups (p < 0.05). The expressions of tight junction genes zo-1, claudin-1, and claudin-4 were up-regulated in these SB-supplemented groups and most pronounced in the ESB2 group (p < 0.05). Compared with the SB0 group, antioxidant enzyme activities (catalase and superoxide dismutase) and their gene expressions increased in the ESB1, ESB2, and RSB groups (p < 0.05). Immune-related genes il-10 and tgf-β1 were up-regulated in the ESB1 and ESB2 groups, while their il-8, il-1β, and tnf-α were down-regulated (p < 0.05). The ESB2 group had higher intestinal abundance of Firmicutes and Lactobacillus. In conclusion, dietary supplementation with 1500 mg/kg encapsulated SB (ESB2) improved growth, antioxidant capacity, immunity, and gut health in largemouth bass.