Physiological and Biochemical Parameters of Fingerlings of Native Carassius auratus gibelio (Bloch, 1792) and Invasive Perccottus glenii (Dybowski, 1877) Species of Fish in the Floodplain Lake Krugloye (Saratov Reservoir)

Using the example of Lake Krugloye (Mordovinskaya floodplain in the Saratov Reservoir), the changes in the physiological and biochemical parameters in two abundant fish species inhabiting the same biotopes have been comparatively analyzed. The fish under study are the aboriginal crucian carp ( Carassius auratus gibelio ) (Bloch, 1792) and the invasive Amur sleeper ( Perccottus glenii ) (Dybowski, 1877). The study reveals differences between the species in the patterns of the dynamics of body weight and contents of protein, fat, water, and caloric contents upon an increase in body length during various months of the active feeding period. Potential reasons for the differences and their consequences are discussed.