RESUMEN
Three trace heavy metals viz., nickel, copper and zinc were studied for their toxic action against Poecilia retriculata (Peters). Among these, copper was found to be most active followed by zinc and nickel. Accumulations of these metals as well as behavioural studies were carried out after exposing fish to sub-lethal concentration of LC20. It was found that the highest quantity of nickel was accumulated in the fish body followed by zinc and copper. After exposure to sub-lethal concentration of metals some behavioural changes in fish were observed due to stress, such as mucus like secretion over gills, excessive excretion, anoretic condition and increased distance between gills and operculum. In all the cases fin movement was observed. Role and use of such changes as biological indicators or as biological early warning system in water quality assessment has been discussed.