A formulated diet improved digestive capacity, immune function and intestinal microbiota structure of juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) when compared with chilled trash fish

Abstract

The effects of two diets on the growth, intestinal microbiota, digestive enzymes, immunity-related enzymes and gene expression were assessed in the juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). Hybrid grouper were fed either a formulated diet (FM group) or chilled trash fish (CTF group). Following a 10-week feeding study, the results showed that the final weight, weight gain rate, specific growth rate and survival rate of fish were not significantly different between the groups. However, bio-economic analysis of the feeds showed that the profit from fish in the FM group was significantly higher than from the CTF group. In addition, digestive enzyme (trypsin and pepsin) activities in fish were significantly higher in the FM group, while lysozyme activity was significantly higher in the CTF group. Levels of complement component 4 (C4) and immunoglobulin M (IgM) in fish serum were significantly lower in FM group fish, while complement component 3 (C3) levels were higher in FM group fish. In the fish intestine, IgM levels were significantly higher in the FM group, while lysozyme activity and C3 and C4 levels were higher in the CTF group. The expression of innate immune genes (MHC II β and TLR22) and inflammatory cytokines (IL-1β, IL-6, IL-10, TNF α1 and IFN γ) were significantly lower in the FM group. The bacterial community of the distal intestine was analyzed by Next-Generation Sequencing. At the phylum level, the relative abundance of Acidobacteria was significantly lower in the FM group, while the abundance of Bacteroidetes was lower in the CTF group. At the family level, the relative abundance of Flavobacterium was significantly lower in the FM group, while the abundance of Bacteroidales_S24-7_group and Lachnospiraceae was lower in the CTF group. The most significantly changed pathways between the two groups were metabolism and genetic information processing. The overall results showed that feed bio-economics, digestive capacity, and immunity of hybrid grouper were superior in the FM group compared to the CTF group.