Saccharomyces cerevisiae extracts improved the effects of a low fishmeal, complex plant protein diet in the orange-spotted grouper, Epinephelus coioides

Abstract

Six iso-nitrogenous and iso-lipidic experimental diets were formulated to evaluate the effects of Saccharomyces cerevisiae extracts, as part of a low fishmeal diet with a complex plant protein source, on the orange-spotted grouper (Epinephelus coioides). In positive control group, fishmeal was the only protein source (FM). The negative control group (Y0) was fed low amounts of fishmeal, and plant protein was used as the protein source. The other diets were supplemented with Saccharomyces cerevisiae extract: 1 g/kg (Y1), 2 g/kg (Y2), 5 g/kg (Y5), and 10 g/kg (Y10). The Epinephelus coioides were divided into six groups, with three replicates per group and 30 groupers per replicate. The experiment lasted for 56 days. The results showed that there was no significant difference in weight gain rate and specific growth rate of FM, Y0 and Y2 groups (P > 0.05). In foregut, mucosal folds length in Y2 group was significantly greater than that in Y0, Y1 and Y10 groups (P < 0.05). The muscle thicknesses of foregut in Y2 and Y5 groups were significantly higher than those in other groups (P < 0.05). The muscle thicknesses of midgut and hindgut in Y2 group were significantly higher than those in Y0 group (P < 0.05). IL-1β and TNF-α in Y1 group were significantly downregulated compared with Y0 group (P < 0.05). After Vibrio harveyi challenge, survival rate in Y1 and Y10 groups was significantly greater than that in Y0 group (P < 0.05). These results indicated that compared with the negative control group, the addition of 2 g/kg S. cerevisiae extract could increase the mucosal folds length of the foregut, and the muscle thickness of the entire intestine, and maintain the growth similar to that of the positive control group. Adding S. cerevisiae extract to feed may improve the immune capacity of E. coioides, but the improvement was not obvious under the challenge of V. harveyi.