Effect of salinization and higher water temperature on fish blood in boreal water bodies: experimental study on perch Perca fluviatilis juveniles in Kama river basin (Perm Krai, Russia)

As a result of secondary salinization of freshwater ecosystems the biota significantly changes, which results in declining the abundance and species diversity of aquatic organisms. This study aims experimental assessment of the hematological parameters of the juvenile perch Perca fluviatilis (Linnaeus, 1758), held at normal (background), as well as elevated mineralization and temperature. The experiment was carried out in August 2021 on perch YOY (young-of-the-year) collected by a fry seine in the lower reaches of the river Gaiva (Perm Kray). We presented the results of studying the peripheral blood of perch juveniles under natural temperature (8.7 ± 0.12 oC) and mineralization (0.26 ± 0.01 g/l) – a control group, as well as the species put into the aquariums 1) with natural temperature and high mineralization (5.3 ± 0.03 g/l), and 2) with higher temperature (19.7 ± 0.12 oC) and higher mineralization. At the end of the experiment (on 35th day) the peripheral blood samples (general analysis) were analyzed. The various destructive disorders of red blood cells were separately identified. The fish held in the highly mineralized water have lower hemoglobin levels, lower hematocrit and deformed blood elements, higher average volume of red blood cells, which indicates the suppression of hematopoiesis. The following disorders of erythrocytes were revealed in the studied fish: poikilocytosis, centric arrangement of the nucleus, scalloped contour, vacuolization of cytoplasm, agglutination, hypochromasia, chromatinolysis, anisocytosis (increase in size), hemolysis, nuclear shadows, formation of schistocytes. In fish contained in the aquariums with increased mineralization the number of aberrant erythrocytes was found higher than in fish from the control group. Combination of increased mineralization with increased temperature leads to the onset of the fourth stage of toxicosis resulting in a mass death of fish.