Water pollution plays a primary role in the destruction of aquatic ecosystems. Anthropogenic activities involve the increased release of various toxic chemicals which ultimately reach the aquatic environments and become responsible for their degradation. Toxicity in fish is the culmination of a series of events involving various physical, chemical, and biological processes. The present investigation was planned to have a deeper insight into various toxicological changes with the impact of heavy metals copper and zinc on different freshwater fishes Channa punctatus and Heteropneustes fossilis. The main objectives were to investigate its toxicity on histological alteration of the gill of these experimental fishes. The percentage of mortality was significantly increased with the increase in concentrations of the copper and zinc toxicant at 96 hr duration of the experiment (F=848.13: C. punctatus; F=1122.78: H. fossilis; p<0.05: for copper, and . F=1393.42: C. punctatus; F=1649.67: H. fossilis; p<0.05: for zinc). On the basis of mortality of C. punctatus and H. fossilis under the exposure of copper and zinc heavy metals, LC10, LC25 and LC50 values were calculated by probit analysis. The histopathological observations resulted that the severity and frequency of organ lesions were found to be more pronounced in fish treated with higher concentrations and even low concentrations at long-term exposure of heavy metals. The heavy metals induced marked histopathological changes in the gills the changes induced the bulging of the tip of the primary gill filament with distortion of the shape of the secondary filament gill lamellae. There was the tendency of fusion of disorganised secondary gill filament, epithelial proliferation, necrosis and haemorrhage in the central venous sinus of primary gill lamellae, congestion of blood vessels, hypertrophy of epithelial cells, clumping of chloride cells, pillar cells and blood channels, lamellar aneurysm and oedema in blood vessels and secondary lamellae.
Kumar et al. (Wed,) studied this question.