Influence of fish protein hydrolysate on intestinal health and microbial communities in turbot Scophthalmus maximus

Abstract

This study aimed to investigate the effect of fish protein hydrolysate (FPH) on intestinal microbiota and health of turbot Scophthalmus maximus (average initial body weight 25.5 g). Two control diets were formulated to contain 360 g kg −1 (high fish meal, HFM) and 240 g kg−1 (low fish meal, LFM) of fish meal. Two experimental diets were derived from the HFM diet by replacing fish meal with FPH at levels of 100 g kg−1 (appropriate level, FPH10) or 300 g kg−1 (excessive level, FPH30). The supplementation of FPH at an appropriate level showed a positive effect on growth performance. According to chyme amino acid concentrations, moderate FPH in diets can alleviate the rate of amino acid absorption in middle intestine than excessive one (FPH30), and more thoroughly absorbed in distal intestine than fish meal (HFM) and plant protein (LFM). Histology of distal intestine showed that an appropriate level of FPH in diets could serve to alleviate the symptoms of structural damage (villi height and wall thickness) to the intestine caused by plant protein. The expressions of tight junction proteins and mucin 2 in the FPH10 and FPH30 diets was up-regulated in middle intestine compared to the LFM diet. FPH at a moderate level reduced the levels of pro-inflammatory factors (IL-1β and TNF-α) but didn't increased anti-inflammatory factors (IL-10 and TGF-β) in middle intestine compared with the LFM diet. To turbot, mucosa and chyme-associated microbiota from middle and distal intestine mainly belonged to Proteobacteria and Firmicutes. The bacterial richness, diversity and/or evenness decreased in middle intestine chyme, distal intestine mucosa and/or chyme when fish were fed diets containing FPH. Fish fed an appropriate level of FPH showed an increase of genera Bacillus in middle intestine mucosa and a decrease of genera Vibrio in distal intestine mucosa, while there was an inverse trend in fish fed an excessive level of FPH. Overall, FPH at an appropriate level showed a positive effect on intestinal health by improving middle or distal intestinal structure integrity and barrier function, as well as regulating immune-related inflammatory factors. Meanwhile, moderate FPH in diets may modulate the abundance of potentially probiotic (Bacillus) and pathogenic (Vibrio) in the intestine.