Relative toxicity of aldrin, fenvalerate, captan and diazinon to the freshwater food-fish, Clarias batrachus.

The median lethal concentrations (LC50S) of aldrin, fenvalerate, captan and diazinon were determined for Clarias batrachus by trimmed Spearman-Karber method. The potency ratios of toxicity among them were analysed by parallel-line bioassay with quantal responses. The LC50S for 40 day of exposure of aldrin, fenvalerate, captan and diazinon were 0.00036, 0.0094, 0.5473 and 2.4186 ppm respectively. These values were lower than those obtained for an exposure of 96 hour. It shows the greater toxicity of the pesticides in a long-term exposure. The relative toxic potency of aldrin fenvalerate, captan and diazinon was in a ratio of 6807:241:4:1 respectively. Thus the chemically different groups of pesticides exhibit an order of toxicity as aldrin greater than fenvalerate greater than captan greater than diazinon for the freshwater catfish, Clarias batrachus. It infers that the catfish is most sensitive to aldrin and least sensitive to diazinon. The comparison of the sensitivity of various species tested against these pesticidal chemicals has also been done to review the available information.