To improve the growth efficiency and biomass accumulation rate of fish grown in aquaculture, it is necessary to have information on the activity of digestive enzymes and the composition of the intestinal microbiota involved in the digestion of the main components of the feed. In our work, we studied for the first time the activity of glycosidases and proteinases in the intestinal mucosa and chyme, as well as the composition of the intestinal microbiome of two size groups of African catfish Clarias gariepinus grown in tanks with a closed water supply system. Total amylolytic and total proteolytic activities were significantly higher in small fish compared to large ones, the activity of disaccharidases (sucrase and maltase) in the intestinal mucosa did not depend on the fish size. In both size-age groups of African catfish, five bacterial phyla dominated: Pseudomonadota, Bacillota, Actinomycetota, Fusobacteriota and Bacteroidota. In the group of small fish, Pseudomonadota accounted for almost half of the number of intestinal bacteria; in large catfish, the distribution of these bacterial phyla was more uniform. For the first time, a relationship was found between the activity of digestive enzymes and the relative abundance of bacteria of different taxa. The highest positive correlation in the chyme of small catfish was found for the total proteolytic activity with bacteria of the order Lactobacillales of the class Bacilli; in large catfish, with bacteria of the orders Actinomycetales and Bacillales, and the total amylolytic activity with bacteria of the order Fusobacteriales and Clostridiales (Eubacteriales). The data obtained can be used to adjust the composition of the microbiome and digestive enzymes in order to obtain greater biomass of catfish in aquaculture.
E. G. Skvortsova (Wed,) studied this question.