Dietary replacement of fish meal with peanut meal in juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂): Growth performance, immune response and intestinal microbiota

Abstract

The objective of the present study was to assess the effects of substituting fishmeal (FM) with peanut meal (PNM) on growth performance, immunity, and intestinal microbiota in juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). Hybrid grouper (initial weight 16.85 ± 0.02 g) were fed diets (isonitrogenous and isolipidic) with PNM replacement rates of 0% (FM), 10 % (PNM10), 20 % (PNM20), 30 % (PNM30), 40 % (PNM40) and 50 % (PNM50) FM protein, respectively. The growth trial lasted for a 10-week period. The results showed that FM replaced by PNM had no significant effect on the growth performance, feed utilisation, somatic indices, and whole-body composition of hybrid grouper (P > 0.05). Acid phosphatase first became more active and then less active with the increased replacement level (P > 0.05), while the activities of lysozyme and the contents of immunoglobulin M in the intestine were significantly enhanced (P < 0.05). The distal intestinal mRNA expression of major histocompatibility complex class II β and toll-like receptors 22 were significantly up-regulated with the increased replacement rate (P < 0.05), but with replacement rates of up to 50 %, there was no significant difference from the FM group (P > 0.05). The mRNA expression of epinecidin and hepcidin in the PNM40 and PNM50 groups was significantly lower than in the FM group (P < 0.05). The gut bacterial community of the distal intestine was analysed by Next-Generation Sequencing. At the phylum level, the relative abundance of Bacteroidetes increased first and then reduced with the increasing rate of replacement, reaching the maximum in the PNM20 group. At the family level, the relative abundance of Bacteroidales S24-7 group had the same trend. The relative abundance of Vibrionaceae grew with the increased replacement level, reaching the maximum in the PNM50 group. Functional predictions of the distal intestinal microbiota indicated that the folding, sorting, and degradation pathway was significantly diminished with the increased replacement level (P < 0.05). The glycan biosynthesis and metabolism, and the immune system pathway of the PNM50 group were significantly lower than those of the FM group, while the metabolism of terpenoids and polyketides showed an opposite trend (P < 0.05). In conclusion, replacing FM with PNM of up to 50 % had no significant negative influence on growth performance, but obviously changed the immunity and intestinal microbiota of juvenile hybrid grouper (E. fuscoguttatus ♀ × E. lanceolatus ♂).