In aquarium experiment, the effect of nickel on the activity of lysosomal glycosidases in the soft tissues of one of the most common mollusks in the littoral was studied. Mussels collected from collectors for their cultivation were acclimated for two weeks to laboratory conditions at different salinities (25‰ and 15 ‰). Then the shellfish were kept for 1, 3 and 10 days in water with different concentrations of nickel cations (10, 100 and 500 μg/l). The activity of four lysosomal glycosidases (ɑ-glucosidase, β-glucosidase, β-galactosidase and β-glucuronidase) was determined in the hepatopancreas and gills of mussels. It was shown that both factors (desalination and ecotoxicant), individually and in combination caused a significant change in the activity of the studied enzymes. An increase in the activity of almost all glycosidases in the organs of mussels at a salinity reduced to 15 ‰ indicates the use of glycogen as the main energy source in adaptive reactions, as well as their possible participation in the biosynthesis of substances necessary at this time, that regulate metabolism. At normal salinity (25 ‰), the effect of nickel was manifested by both a decrease and an increase in the activity of ɑ- and β-glucosidases, depending on the concentration and time of exposure to the metal. The activity of glucuronidase in most cases increased under the influence of nickel, which indicates the participation of this enzyme in detoxification and elimination of toxicants from the body. A multidirectional reaction of the lysosomal apparatus of the hepatopancreas and gills to the presence of this metal in the environment was revealed. The phase nature of adaptive metabolic changes in mussels under environmental stress conditions is discussed.