author(s)
Muneesh kumar, Mansa Ram

abstract
The environment is impacted by ongoing pollution, caused by both natural factors and human activities such as industrialization and mining. Heavy metals are a major problem because they are toxic and tend to accumulate in living organisms. This study was carried out on juvenile Clarias batrachus (L.) to investigate the effects of sub-lethal concentrations of copper and zinc (0.3, 0.4, 0.5 ppm) on the survival rate, oxygen consumption and histopathological changes in the gills of exposed fish. The results showed a decrease in survival rate with increasing concentration of each metal. Copper has the most toxic effect compared with zinc the survival rate has decreased from 50% to 10% for copper and from 70% to 20% for zinc with increasing concentration for 15 days. Oxygen consumption rate decreased with increasing concentration and there was a negative correlation between oxygen consumption and metal concentration. The exposure to each metal caused histopathological changes in the gill and resulted in separation of epithelial secondary gill lamellae, hyperplasia, fusion of secondary lamellae and necrosis.