The acute toxicity of heavy metal salts onDaphnia similis Claus is studied in terms of LC50. Copper is found to be the most toxic and zinc the least. Toxicity of the heavy metals is studied by observing changes in the longevity, body length, fecundity and moulting frequency of the animal. The decreasing order of toxicity of heavy metals on the longevity, body length and fecundity is indicated by Zn>Pb>Cu>Hg, Cu>Zn>Hg>Pb and Pb>Cu>Zn>Hg respectively. The average number of instars increased with the increase of the concentration of metals in the medium. The order of accumulation pattern is Zn>Pb>Cu for 24 h and Zn>Cu>Pb for 48 h. On doubling the concentration of metal to whichDaphnia similis is exposed and fed to the fishSaratherodon mossambicus, the biomagnification increases for copper and zinc while it decreases for lead.