Modern aquaculture is rapidly developing. It includes food fish farming and decorative fish breeding. Like in any fast-growing livestock industry, there may be problems related to the health offish. Carp is the main object in Russian fish farming, representing the basic type of unpretentious, omnivorous and fast-growing pond polyculture. Tilapia is one of the most preferred species of global aquaculture, due to its hardiness, rapid weight gain and ability to tolerate high planting density. Discus is the most popular of the ornamental fish species; it features a large number of color variations, interesting behavior and is cost-effective in breeding. The authors carried out comparative physiological assessment of bony fish of the cyprinid and cichlid families. Hematological parameters were determined - erythrocyte and leukocyte formulas (by means of differential analysis techniques); biochemical parameters of blood serum (with the analyzer), the average cytochemical coefficient of lysosomal cationic protein content in fish blood neutrophils. The research results showed specific features in the intensity of erythro- and leukopoiesis, the proportion of granular cells of the myeloid series. It was revealed that the peculiarity of discus is the presence of blast forms of white blood cells in the blood: myeloblasts, promyelocytes, and myelocytes. In the blood of tilapia, in contrast to discus and carp, there is a high content of granulocytes: neutrophils, eosinophils and basophils of monocytes and lymphocytes in the leukogram. Differences between species were noted based on the results of the lysosomal cation test. The difference in a number of biochemical parameters can also be seen: in tilapia as compared with other species - in the content of albumins, alkaline phosphatase and ALT, in discus - in the activity of lactate and KK enzymes.