In this study, we evaluated the effects of fermented soybean meal (FSBM) or/and unfermented SBM replacing a portion of fish meal (FM) on the growth performance, antioxidant capacity, immunity, and mechanistic target of rapamycin (mTOR) signaling pathway of juvenile coho salmon (Oncorhynchus kisutch). Four groups of juvenile coho salmon (initial weight 152.23 ± 3.21 g) in triplicate were fed for 12 weeks on four different iso-nitrogen and iso-lipid experimental diets: G0 diet (28% FM protein, control group), G1 diet (18% FM protein and 10% SBM protein), G2 diet (18% FM protein, 5% SBM protein, and 5% FSBM protein), and G3 diet (18% FM protein and 10% FSBM protein). The main results were compared with the G0 diet; the weight gain rate, specific growth rate, and condition factor of juveniles in G3 were increased significantly ( ). The content of muscle crude protein, the total protein, glucose, albumin, total cholesterol in serum, and the total antioxidant capacity in the liver of juveniles in G3 was increased significantly ( ). The activities of pepsin, trypsin, α-amylase, and lipase in the intestine, the superoxide dismutase, catalase, and alkaline phosphatase in the liver of juveniles in G3 were increased significantly ( ). The expression levels of phosphatidylinositide 3-kinases, serine/threonine kinase, mTOR, and ribosomal protein S6 kinase 1 genes in the liver of juveniles in G3 were upregulated significantly ( ). The feed coefficient ratio, viscerosomatic index, the contents of muscle moisture, and malondialdehyde in the liver of juveniles in G3 were decreased significantly ( ). The expression levels of tumor necrosis factor α, interleukin 1β, and interleukin 6 genes in the liver of juveniles in G3 were downregulated significantly ( ). However, there was no significant effect ( ) on the survival rate, food intake, and muscle crude lipid and ash of juveniles among the experimental groups. In conclusion, FSBM to replace a portion FM had a positive effect on the growth performance, protein deposition, antioxidant enzyme activity, digestive enzyme activity, protein synthesis, and immune-related genes of juvenile coho salmon.

This study evaluated the impact of Bacillus subtilis supplementation on growth, antioxidant status, digestive enzyme activities, hematological parameters, blood biochemistry, and immune responses in Nile tilapia (Oreochromis niloticus) fingerlings. A total of 180 fingerlings (mean weight: 5 ± 0.5 g) were randomly assigned to four groups: a control group and three probiotic-supplemented groups with 10⁶ (S-1), 10⁸ (S-2), and 10¹⁰ (S-3) CFU g⁻¹ of B. subtilis, following a completely randomized design. Fish were fed twice daily for eight weeks. Results showed that the 10¹⁰ CFU g⁻¹ group exhibited significantly higher weight gain (43 g), specific growth rate (2.5%/day), and better feed conversion ratio (0.7) compared to the control (30 g, 2.2%/day, and 1.4, respectively). Hematological parameters (WBC, RBC, hemoglobin) and immune responses (phagocytic activity, lysozyme) were significantly improved. Blood biochemistry showed decreased ALT/AST levels and increased ALP activity. Digestive enzymes (protease, lipase, amylase) and antioxidant activity (GPx, CAT, SOD) were enhanced, with reduced MDA levels. No significant differences were observed in survival rates or stress responses. These findings suggest that B. subtilis supplementation at 10¹⁰ CFU g⁻¹ improves growth, immune function, and antioxidant status, making it a promising probiotic for Nile tilapia.

This study aims to investigate the effects of partial dietary replacement of fish meal with unfermented and/or fermented soybean meal (fermented by Bacillus cereus) supplemented on the growth performance, whole-body composition, antioxidant and immunity capacity, and their related gene expression of juvenile coho salmon (Oncorhynchus kisutch). Four groups of juveniles (initial weight 159.63 ± 9.54 g) at 6 months of age in triplicate were fed for 12 weeks on four different iso-nitrogen (about 41% dietary protein) and iso-lipid (about 15% dietary lipid) experimental diets. The main results were: Compared with the control diet, the diet with replaced 10% fish meal protein with fermented soybean meal protein supplementation can significantly (p < 0.05) influence the expression of superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, nuclear factor erythroid 2-related factor 2, tumor necrosis factor α and interleukin-6 genes, the growth performance, the serum biochemical indices, and the activity of antioxidant and immunity enzymes. However, there was no significant effect (p > 0.05) on the survival rate (SR) and whole-body composition in the juveniles among the experimental groups. In conclusion, the diet with replaced 10% fish meal protein with fermented soybean meal protein supplementation could significantly increase the growth performance, antioxidant and immunity capacity, and their related gene expression of juveniles.

Vitamin C (VC) plays an essential role in fish physiological function and normal growth. However, its effects and requirement of coho salmon Oncorhynchus kisutch (Walbaum, 1792) are still unknown. Based on the influences on growth, serum biochemical parameters, and antioxidative ability, an assessment of dietary VC requirement for coho salmon postsmolts ( g) was conducted with a ten-week feeding trial. Seven isonitrogenous (45.66% protein) and isolipidic (10.76% lipid) diets were formulated to include graded VC concentrations of 1.8, 10.9, 50.8, 100.5, 197.3, 293.8, and 586.7 mg/kg, respectively. Results showed that VC markedly improved the growth performance indexes and liver VC concentration, enhanced the hepatic and serum antioxidant activities, and increased the contents of serum alkaline phosphatase (AKP) activity, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and total cholesterol (TC) whereas decreased the serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) activities, and triglyceride (TG) level. Polynomial analysis showed that the optimal VC levels in the diet of coho salmon postsmolts were 188.10, 190.68, 224.68, 132.83, 156.57, 170.12, 171.00, 185.50, 142.77, and 93.08 mg/kg on the basis of specific growth rate (SGR), feed conversion ratio (FCR), liver VC concentration, catalase (CAT), hepatic superoxide dismutase (SOD) activities, malondialdehyde (MDA) content, and serum total antioxidative capacity (T-AOC), AKP, AST, and ALT activities, respectively. The dietary VC requirement was in the range of 93.08–224.68 mg/kg for optimum growth performance, serum enzyme activities, and antioxidant capacity of coho salmon postsmolts.