Impacts of diet on hindgut microbiota and short-chain fatty acids in grass carp ( Ctenopharyngodon idellus).

Diet is known to influence intestinal microbiota in fish, but the specifics of these impacts are still poorly understood. Different protein/fibre ratio diets may result in differing structures and activities of gut microbiota. We examined the hindgut microbiome of grass carp ( Ctenopharyngodon idellus) fed three different diets: fish meal ( FM, high protein - low fibre), Sudan grass ( SG, high fibre - low protein) and compound feed ( CF, intermediate). Microbial profiles of fish fed on FM were significantly different from profiles of fish fed CF and SG ( F = 18.85, p < .01). Cetobacterium, known to be positively associated with protein digestion, was the dominant microbial group in FM samples (approximately 75.7%), while Lachnospiraceae and Erysipelotrichaceae, thought to be involved in fermentation of plant polysaccharides, were dominant in CF and SG samples (46.8% and 42.9% respectively). Network analyses indicated that the abundance of Lachnospiraceae and Erysipelotrichaceae was in a significantly positive correlation ( r = .895, p = .001). Short-chain fatty acid ( SCFA) levels may indicate that the digestibility of diet by microbiota in the grass carp gut decreased from FM to SG ( FM> CF> SG). Overall low SCFA levels indicate that hindgut fermentation probably provides a low proportion of energy requirements in grass carp. [ABSTRACT FROM AUTHOR]