Acute toxicity of some heavy metals to fish food organisms

Acute toxicity of four heavy metals (Hg, Cd, Zn and Pb) to the fish food organisms, viz. Daphnia sp. and Cypris sp., has been determined by static bioassay experiments. Even though both Daphnia sp and Cypris sp. have been found to be sensitive to heavy metals (Hg, Cd, Zn and Pb), the experiments led to an observation that Cypris sp. is comparatively more sensitive than Daphnia sp. However, when the individual toxicity of heavy metal is considered, it seems that the toxicity of metals is in the order viz. Hg > Cd > Zn > Pb. The investigation reveals variation in the sensitivity of different organisms to the same toxicant and variation in the sensitivity of different metals.