Biometric and histopathological parameters of rainbow trout with a decrease in animal protein content in the diet

Comparative studies of the effect of replacing animal protein with vegetable protein in the diet structure on biometric indices and histopathologic indices of rainbow trout liver were carried out on biological models of rainbow trout. Inclusion of white lupine with a shell in the composition of mixed fodder led to an increase in the weight of the intestine. In the 1st experimental group in relation to the control the mass of intestine increased by 26,3 %, in the 2nd experimental group it decreased by 22 %. The main place of absorption is the anterior intestine and the area adjacent to the pyloric appendages, where at optimal feeding can be resorbed up to 90% of proteins, fats and carbohydrates from the total amount that is available to fish from food. The stomach of rainbow trout also takes an active part in the absorption of nutrients (29 % of proteins, 44 % of lipids and 26 % of carbohydrates). In our experiment, stomach weight increased in the 1st experimental group by 2.61 % and in the 2nd experimental group by 7.3 %. The analysis of the studied literature data allows us to assert that the decrease in intestinal weight in the 2nd experimental group, where 25 % lupine without shell was used in the diet structure, resulted in more intensive digestion of nutrients in its cranial part. The increase in intestinal weight in the 1st experimental group is associated with the use of lupin with a shell, which led to adaptation of trout, expressed in morphological changes in the intestine under the influence of fiber. Examination of liver tissue in the 2nd experimental group revealed some degenerative changes. Vacuolization of liver cells in the 2nd experimental group, in which the diet with increased content of vegetable protein in its structure was applied, was significantly lower, and accordingly, this group had the smallest hepatocytes. Defects of cell contacts in the liver, destruction, and proliferation of cells of the lymphohistiocytic series into sinusoids were observed. Thus, reduction in the structure of diets of predatory fish of animal origin feeds to the level of 25 % leads to liver degeneration. This reactive adaptation of the liver to a new plant protein ingredient is short-term.