Supplementation with Saccharomyces cerevisiae hydrolysate in a complex plant protein, low-fishmeal diet improves intestinal morphology, immune function and Vibrio harveyi disease resistance in Epinephelus coioides

Abstract

Six iso‑nitrogenous and isolipid experimental diets were fed to orange-spotted groupers, Epinephelus coioides, and their growth performance, intestinal morphology, immune function and resistance to Vibrio harveyi infection evaluated. Positive controls (FM) were fed fishmeal as the only protein source. Negative controls (Y0) were fed a lower proportion of fishmeal in combination with plant proteins. The other groups were fed the Y0 diet supplemented with Saccharomyces cerevisiae hydrolysate at proportions of 10 g kg−1 (Y1), 20 g kg−1 (Y2), 30 g kg−1 (Y3) and 50 g kg−1 (Y5). Some 540 juvenile E. coioides (initial weight: 10.00 ± 0.05 g) were randomly divided into six groups, each with three replicates and 30 groupers per replicate. The experiment lasted 56 days. Rates of weight gain, special growth, feed coefficient and survival were not significantly influenced by diet. In the foregut and midgut, the villus length in group Y3 and muscle thickness in group Y1 were significantly higher than those in group FM. The expression levels of TLR22, INF-γ, and TNF-α were significantly higher in group Y0 than in Y1, Y2, Y3 and Y5. After V. harveyi challenge, the survival rate was significantly lower in group Y0 than in FM, while dietary supplementation with S. cerevisiae hydrolysate at 10 g kg−1 and 20 g kg−1 (Y1 and Y2) improved survival compared with group Y0 to a level comparable to that of group FM. These results indicate that a low-fishmeal diet supplemented with complex plant proteins and S. cerevisiae hydrolysate provides similar growth performance to a diet with fishmeal as the only protein source. Supplementation with S. cerevisiae hydrolysate increased the villus length and muscle thickness in the foregut and midgut, reduced the expression of intestinal inflammatory factors, and significantly improved resistance to V. harveyi infection.