Effects of dietary Saccharomyces cerevisiae fermentation product (DVAQUA®) on growth performance, intestinal autochthonous bacterial community and non-specific immunity of hybrid tilapia (Oreochromis niloticus ♀×O. aureus ♂) cultured in cages

In the present study, hybrid tilapias (Oreochromis niloticus ♀ × O. aureus ♂) were fed six isonitrogenous and isoenergetic experimental diets in cages. The diets contained six levels of Saccharomyces cerevisiae fermentation product (DVAQUA®): 0 (CK), 0.125 (G1), 0.25 (G2), 0.5 (G3), 1.0 (G4) and 2.0 (G5) g kg− 1 diet. The purpose of this study was to evaluate the effects of dietary DVAQUA on growth performance, intestinal autochthonous bacterial community by using 16S rDNA and denaturing gradient gel electrophoresis (DGGE), and non-specific immunity of hybrid tilapia. Supplementation of dietary DVAQUA showed no effects on growth performance, diet conversion and survival rate of the hybrid tilapia. However, supplementation of DVAQUA affected the autochthonous gut bacteria community. Various potentially beneficial bacteria were stimulated by dietary DVAQUA at different feeding period, while potential harmful species such as Escherichia coli serotype O20: H42-like, uncultured Bacilli bacterium clone MS030A1_F02-like, and Pseudomonas fluorescens strain YC0357-like were depressed by dietary DVAQUA. Non-specific immunity of hybrid tilapia such as serum lysozyme activity, serum alternative complement pathway (C3 and C4) activities, head kidney macrophage phagocytic activity, and head kidney macrophage respiratory burst activity were improved by dietary DVAQUA. The optimum dose of dietary DVAQUA for hybrid tilapia determined based on a broken-line approach varies depending on the variables used: 0.226, 0.467, 0.492 or 0.50 g kg− 1 diet for lysozyme, C3, C4, or phagocytic activity, respectively.