For the first time, the activity and pH dependence of digestive enzymes were studied in fish living in the Mekong Delta: glass perch Parambassis wolffii, small-scale croaker Boesemania microlepis, Pangasius Pangasius macronema and fish of the family. Cyprinidae. Significant interspecific differences in the level of activity of peptidases and glycosidases providing hydrolysis of protein and carbohydrate components of food were revealed. The greatest interspecific differences are characteristic of glycosidases: the level of enzymatic activity in fish of the family. Cyprinidae exceeds those of the glass perch P. wolffii by 13.6 times. The differences in the level of peptidase activity in fish of different species are lower: in the case of the activity of stomach enzymes in the glass perch P. wolffii, it is 1.8 times higher than that of the pangasius P. macronema, in the case of the total activity of stomach and intestinal enzymes in the same species – 1.5 times. The obtained data confirm the ideas about the dependence of the activity of digestive hydrolases on the spectrum of fish nutrition. The activity of intestinal enzymes decreases significantly in the acidic ph zone than in the alkaline one. Consequently, acidification of the enteric environment will negatively affect the digestive processes in these fish species.