Fermentation of dietary carbohydrates to short-chain fatty acids by gut microbes and its influence on intestinal morphology of a detritivorous teleost tilapia (Oreochromis niloticus)

Fermentability of dietary cellulose, sodium alginate, chitin, α-starch and kaolin (non-fermentable control) by gut microbes was compared in a tilapia, Oreochromis niloticus, fed a diet containing one of the above supplements (150 g · kg⁻¹) for 14 days. The thickness of the tunica muscularis was also compared among fish fed these diets. The concentration of short-chain fatty acids (SCFA) in gut contents was higher in fish fed the α-starch than in fish fed the sodium alginate, chitin, or kaolin diets. Intestinal contents from fish fed the kaolin (control) diet were incubated in batch culture with each of the other supplements. The volume of released gas and production of SCFA for 24 hr was greater with a α-starch as a substrate than in those with the other substrates. The thickness of the tunica muscularis differed among dietary groups but villus height did not. Fish fed chitin or α-starch had a thicker tunica muscularis than those fed cellulose or sodium alginate. These results suggest that this detritivorous fish digests α-starch to produce SCFA in the intestine by microbial fermentation.