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Although β-glucan has diverse benefits for fish health, the potential adverse impacts of excessive supplementation are poorly understood. This study investigated the optimal dosage of β-glucan for coral trout and explored the adverse effects of excessive supplementation. The results revealed that moderate β-glucan supplementation (1) significantly enhanced the weight gain rate and specific growth rate (SGR); (2) significantly improved the intestinal villus length (0.10%), muscle thickness (0.05–0.15%), and α-amylase and chymotrypsin activities (0.05–0.15%); (3) significantly increased liver catalase (CAT), glutathione reductase (GR), alkaline phosphatase, complement 3, immunoglobulin M (IgM), lysozyme, serum superoxide dismutase, CAT, glutathione peroxidase, GR, total antioxidant capacity, acid phosphatase, complement 4, and IgM activities and significantly reduced malondialdehyde contents; (4) upregulated genes in the liver associated with copper-zinc superoxide dismutase (SOD-1), manganese superoxide dismutase (SOD-2), CAT, GSH-Px1a, ACP6, AKP, LZ-c, IgM, C3, and C4-b. However, 0.20% β-glucan significantly inhibited the growth performance of coral trout compared with 0.10% β-glucan. Thus, 0.10% β-glucan represents the optimal dosage for promoting growth, antioxidant activity, and immune responses in coral trout, while higher β-glucan levels weakened these beneficial effects. With an SGR established by a cubic regression analysis, the optimal level of β-glucan for maximal growth of coral trout is 0.082%. This study provides new insights into the health impacts of β-glucan on fish. [ABSTRACT FROM AUTHOR]

The effects of three feed additives in a low fish meal diet on growth, antioxidant capacity and intestinal microbiota of Penaeus monodon were studied to enhance the understanding of these effects and to provide basic data and a reference for the formulation and optimization of feed for P. monodon. A total of 630 healthy, homogenous shrimp (4.58 ± 0.05 g) were randomly divided into seven groups with three replicates per group and 30 shrimp per replicate in a breeding barrel (500 L). The additive names and amounts were 0 (CT); vitamin B6, 100 mg/kg (V1); vitamin B6, 200 mg/kg (V2); phytase, 1000 U/kg (P1); phytase, 2000 U/kg (P2); 0.2% yucca extract (Y1); and 0.4% yucca extract (Y2). The experiment lasted 8 weeks. The results showed that compared to CT, V1 and Y1 had a significant increasing tendency toward weight gain (WG) (p < 0.05) and had a significant decreasing tendency in the food conversion ratio (FCR) (p < 0.05). P2 had a significant increasing tendency in α-amylase activity (p < 0.05), and P1 had a significant increasing tendency in total superoxide dismutase (T-SOD) (p < 0.05). The next-generation sequencing of intestinal microbiota showed that Proteobacteria was the most abundant phylum in the seven groups, accounting for 29.33%, 56.67%, 55%, 45.33%, 73%, 39.33% and 64.33% of the total. Compared to CT, the Proteobacteria was significantly high (p < 0.05) in P2 and Y2, and the Bacteroidota in all other groups decreased significantly (p < 0.05). The functional prediction of FAPROTAX indicated that there was no significant difference (p > 0.05) in functional components among all groups. According to growth performance, antioxidant capacity and effects on intestinal microbiota, vitamin B6 (100 mg/kg), phytase (2000 U/kg) and yucca extract (0.2%) can be recommended as additives for the diet of P. monodon. [ABSTRACT FROM AUTHOR]

The aim of this experiment was to investigate the effects of the partial substitution of fish meal with soybean products and chicken meal on the growth performance, antioxidant capacity and intestinal microbiota of Penaeus monodon. A total of 450 healthy, consistent shrimp were randomly divided into five groups, with three replicates per group and 30 shrimp per replicate. The proportion of fish meal substituted with soybean products and chicken meal in the five feed groups was 0% (FM), 40% (40SC), 60% (60SC), 80% (80SC) and 100% (100SC). The experiment lasted for 8 weeks. The results showed that, compared to the FM group, the 40SC and 60SC groups had a decrease in WG and SR, but there was no significant difference (p > 0.05). In contrast, compared to the FM group, the FCR in the 100SC group was significantly increased (p < 0.05), while there was no significant difference among the FM and 40SC, 60SC and 80SC groups (p > 0.05). Compared to the FM group, the ACP in the 80SC and 100SC groups significantly increased (p < 0.05), while the 40SC and 60SC groups had no significant difference (p > 0.05). The AKP in the 100SC group was significantly higher than that in the FM group (p < 0.05), while there were no significant differences among the other four groups (p > 0.05). There were no significant differences in T-AOC and T-SOD among all the treatment groups (p > 0.05). The next-generation sequencing of the intestinal microbiota showed that Proteobacteria was the most abundant phylum in the five groups, accounting for 37.67%, 66%, 40%, 40% and 43.33%, respectively. Compared to the FM group, the Fusobacteriota in the other four groups decreased significantly (p < 0.05). The functional prediction of FAPROTAX indicated that no functional components were observed which are harmful to the body. Considering the effects on growth performance, antioxidant capacity and intestinal microbiota, it is feasible to use soybean products and chicken meal to replace 60% of fish meal in the feed of P. monodon. [ABSTRACT FROM AUTHOR]

The effects of dietary chitosan (0, 2, 4, 6, 8 and 10 g/kg) on the growth, health condition and disease resistance of golden pompano Trachinotus ovatus were evaluated. Dietary chitosan significantly enhanced weight gain, with the highest observed in fish fed the 6 g/kg chitosan diet. This chitosan level significantly promoted gut health by increasing villus length, lipase and protease activities and intestinal barrier-related genes expression. Meanwhile, dietary 6 g/kg chitosan improved the inflammatory response and anti-oxidative capacity of fish by regulating the expression of genes involved in NF-κB pathway and Nrf2 pathway, respectively. Furthermore, after challenge with Vibrio harveyi for 2 weeks, the survival rate increased significantly when dietary chitosan level was 6 g/kg. Overall, our results indicate that 6 g/kg chitosan is the optimal dose for enhancing growth, health and disease resistance of fish, but excessive chitosan (10 g/kg) weakens its beneficial effects. [Display omitted] [ABSTRACT FROM AUTHOR]