Pollution is one of the major problem which deteriorates the all the levels of life. The present study was planned to investigate Mercury toxicity to a freshwater fish, Channa punctatus. The study is supported by behavioural, morphological and histopathological investigations. The major objective is to assess the feasibility of use of fish scales and gillls as heavy - metal pollution indicators. Mercury one of the heavy metal it has deleterious effects at the behavioural and morphological levels in Channa punctatus and its indiscriminate use should be halted immediately. This shall help in reducing its ill effects to various other non-target species. The feature like fish scale structure; its elemental composition and architectural patterns on gill surface can be successfully used as bioindicators in heavy metal pollution studies.