Influence of heavy metals on physiological and biochemical parameters of Pseudorasbora parva (Cypriniformes, Cyprinidae)

Abstract

Anthropogenic load on aquatic ecosystems leads to increased inputs of heavy metals, which can have a toxic effect on aquatic organisms. Some of the most appropriate objects for research are short-cycle fish species. This article considers the results of studies on the adaptive reactions of the stone moroko Pseudorasbora parva (Temminck et Schlegel, 1846) to Mn, Pb, Ni heavy metal ions, which exceeded the reference values in the reservoir by 1.7, 1.5 and 2.0 times, respectively. Changes in morphological parameters of the blood and histocytological pattern of the hepatopancreas of the experimental species under the influence of toxicants, as well as changes in biochemical parameters, were determined. It was noted that the influence of Mn caused pathological changes in the form of poikilocytosis. The morphometric parameters of erythrocytes (the cell area and the nuclear area) reached 67.48 ± 0.67 and 13.97 ± 0.22 µm2 respectively (4.0% and 13.8% less compared to the control). The influence of Ni resulted in an increased number of leukocytes and immature forms of erythrocytes. The area of erythrocytes was 0.9% smaller than that of the control group, and the area of the nucleus was 4.5% smaller than in the control. The effect of Pb as well as Mn consisted in poikilocytosis. The area of red blood cells and nuclei was smaller by 6.5% and 8.3%, respectively, compared to the control. The percentage of white blood cells in fish exposed to Ni and Pb tended to increase. In the experiment with nickel, the percentage of white blood cells was 10.2% of the number of formed elements; in the experiment with lead – 11.3%; with manganese – 6.1%, while in the control, the number of white blood cells compared to the total number of formed elements of fish was only 1.2%. Cytometric studies have revealed that there are significant differences in the shape, size, and location of hepatocytes in different experimental fish. The structural components of the liver for histological specimens were stained differentially with different intensities and different colours. The hepatocytes on histological specimens of the liver of the stone moroko exposed to Ni and Mn ions did not have clearly defined boundaries, there was a large number of destroyed cells, which indicates the toxic effect of these heavy metals. The hepatocytes exposed to Pb had the largest area of cells and nuclei and the highest nuclear-cytoplasmic ratio is typical for hepatocytes under the influence of Mn. The nuclei had the largest size and occupied 12.7% of the internal contents of the cells. It is shown that under the impact of the studied concentrations of Mn, Ni and Pb, lactate dehydrogenase activity increased by 1.22, 1.14 and 1.48 times compared to the control, respectively. In contrast, there was a 3.27-fold decrease in succinate dehydrogenase activity under the impact of Mn. Besides that, the activity of the enzyme decreased by 1.48 and 1.68 times under the action of Ni and Pb. Subsequently, we found an increase in the activity of alkaline phosphatase in muscle tissue by 3.25–3.94 times under the influence of the studied toxicants. Muscle protein levels under the impact of Mn were 1.14 times lower than in the control, the most distinct decrease in protein was found under the impact of Ni (1.53 times). The obtained data of physiological and biochemical reactions of the stone moroko to the influence of heavy metals provide an opportunity to predict changes in the species composition of fish fauna under conditions of excessive toxic pollution of ecosystems.