Industrialization and anthropological activities has degenerated the environment considerably. This effect is more prominent in developing countries like India, where unperturbed deposition of waste has resulted in the accumulation of heavy metals in the water bodies surrounding these industries. These resulted in toxicity, which causes great threat to freshwater ecosystem and to human health in the long run. The study in this book focuses on these environmental spoilage by two specific heavy metals; Lead (Pb) and Zinc (Zn); which forms the by product of several industries. The level of these metals were measured in the polluted water and also from the tissue of an Indian major carp, (Cirrhinus mrigala), which survives in these water bodies. It was observed that the heavy metal pollution has generated a unique feature in these fishes. The Esterase (isozyme) polymorphism was observed due to the pollutants. Thus enzyme polymorphism can serve as an important parameter for establishing the adaptive ability of a genome to environmental stresses and fluctuations. Thus certain markers in fishes that survive in the eutrophic conditions can help to detect the status of a contaminated niche.