Total replacement of fish meal with soybean meal in diets for bullfrog (Lithobates catesbeianus): Effects on growth performance and gut microbial composition

Abstract

A feeding experiment was carried out to examine the effects of total replacement of fish meal (FM) with soybean meal (SM) on growth performance and gut microbial composition in bullfrog (Lithobates catesbeianus). A basal diet containing 44% FM was used as a FM-based diet and a SM-based diet was produced by entire replacement of FM with SM. The two diets were fed to triplicate groups of bullfrog (40 ± 0.24 g, 14 bullfrogs per aquarium) to apparent satiation twice daily for 8 weeks. The results revealed the significant (P < .05) reduction of weight gain, specific growth rate and feed efficiency by entire substitution of FM with SM. No significant changes in bacterial community richness and diversity were found between gut content and gut mucosa in FM group, and by the shift in dietary protein source. However, a tighter clustering of microbial community was observed in the gut mucosa compared to the gut content. Proteobacteria, Fusobacteria and Firmicutes were the most abundant bacterial phyla in the FM group whereas Fusobacteria and Proteobacteria were the dominating phyla in the SM group. At the genus level, Escherichia-Shigella (58.81%) and Cetobacterium (27.05%) were the most abundant genera in the FM group while in the SM group Cetobacterium showed the highest abundance (76.31%). The FM group exhibited remarkably higher immune function, and carbohydrate metabolism rate while a higher amino acids transport and metabolism were found in SM group. To conclude, the entire replacement of FM with SM led to profound reduction of growth performance and substantial alterations in microbial composition of the gut mucosa of bullfrog.