Low-gossypol cottonseed protein concentrate used as a replacement of fish meal for juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂): Effects on growth performance, immune responses and intestinal microbiota

Abstract

The use of low-gossypol cottonseed protein concentrate (CPC) as a replacement for fishmeal (FM) in the juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) was investigated concerning differences in growth performance, immune response, and intestinal microbiota among the dietary treatments. Hybrid grouper were fed a diet (isonitrogenous and isolipidic) with FM or FM replaced with either 20% (CPC20), 40% (CPC40) or 60% CPC (CPC60) for 10 weeks. At the end of the study, there were no significant differences in the weight gain rate, specific growth rate, survival rate, and feed intake of fish among the groups. However, the feed conversion ratio of fish in the CPC-containing groups was higher than that in the FM group and was significantly higher in the CPC40 and CPC60 group. The levels of immunity-related enzyme activities and gene expression in the fish intestine were also investigated. In the CPC-containing groups, the lysozyme activity and immunoglobulin M levels were significantly increased, while the superoxide dismutase and catalase activities were significantly reduced compared to the FM group. The mRNA expression of innate immune genes (MHC-II-β, TLR22, TNF-α1, IL-6, IFN-γ, and IL-10) of the distal intestine (DI) was significantly increased in CPC-fed fish; however, there was no significant change in the TGF-β1 expression. The bacterial community in the DI was analyzed by Next-Generation Sequencing, which showed no significant difference in alpha diversity among the four diet groups. At the family level, the relative abundance of Burkholderiaceae was significantly higher in the CPC20 group compared to the FM group, while the relative abundance of Bacteroidales S24–7 group and Lachnospiraceae was significantly higher in the FM group. The functional prediction of the microbiota indicated that the pathways of amino acid metabolism, xenobiotics biodegradation and metabolism were significantly more abundant in the CPC-containing groups than the FM group. In contrast, the pathways associated with genetic information processing (translation, replication and repair) were more prevalent in the FM group. These results demonstrated that although dietary CPC replacement of levels up to 60% did not significantly alter the growth performance in hybrid grouper, the immune responses were adversely influenced. Replacing FM with CPC had an important impact on microbial profiles but not on diversity.