The objectives of this work was to examine the toxicological effect and molecular changes caused by a heavy metal pollutant mercuric chloride (HgCl2), in fresh water snakehead Channa punctatus, locally known as Taki fish in Bangladesh. When fishes were exposed to HgCl2, it induced death of the fishes in a concentration-dependent manner. 1 mM, the highest concentration tested in this study, was found to be the deadliest and it induced death of the fishes within 35 to 40 minutes. As the concentration lowered (0.5 mM â€“ 0.1 mM) the survival time increased dosedependently to near about five hours. HgCl2 dissolved in different types of water (such as distilled water, tap water and pond water) was found to have no effects in changing the required time of fish death. We later investigated the effect of HgCl2 on fish liver cells as liver cells are known to be mostly affected by toxic metals. HgCl2 found to decrease liver cell viability to 32% by the higher concentration (1 mM) tested. Liver cell viability increased up to 82% with decreasing concentration of HgCl2 from 0.5 mM to 0.1 mM. To characterize the mechanism of cell death induced by HgCl2, the changes in molecular level was then examined. It was found that the heavy metal induced chromosomal DNA fragmentation and expression of certain proteins.