The seasonal dynamics of lysosomal enzyme activity in the organs of trout Parasalmo mikiss irideus during commercial cultivation in cages was studied. Fish for analysis were obtained from a trout farm located in Kondopoga Bay of Lake Onega. In the liver, kidneys, gills, skeletal muscles, spleen and gonads of fish, the activity of 5 lysosomal enzymes was determined: acid phosphatase, DNase, RNase, β-glucosidase and β-galactosidase. Differences were revealed in comparison with similar indicators for trout from the natural environment. In rainbow trout, like other fish, in nature in autumn-winter period, as the temperature drops, food activity decreases and a transition to endogenous nutrition occurs. The maintenance of physiological processes and the provision of energy occurs due to internal reserves, which are mobilized with the participation of lysosomal enzymes. In winter, the liver exhibits maximum activity of acid phosphatase, which gradually decreases by summer. For trout reared in cages, such a clear relationship is not observed. Perhaps the transition to endogenous nutrition does not occur in them to the same extent as in wild fish, since they are fed during the season, although less often. In male cage trout, acid phosphatase and DNase in the liver showed a decrease in activity in March and two peaks of activity in February and May. This can be attributed to the fact that in May, males of the V stage of gonad maturity, in which a large number of lysosomes involved in fertilization are concentrated, were taken for analysis. The dependence of the activity of lysosomal hydrolases on the functional specificity of organs is shown. High activity of the studied enzymes was detected in the kidneys, spleen and liver – organs that produce cells and protein of the immune system, which protects the body from negative abiotic and biotic factors. Various individual variability of enzymes was revealed. Glycosidases turned out to be the most variable in the processes of adaptation to a complex of endogenous factors affecting farmed trout. The participation of lysosomes in catabolic and anabolic processes, exocytosis of harmful metabolic products and xenobiotics is discussed.