author(s)
Sameena Khan, Imtiyaz Qayoom and Masood H Balkhi

abstract
Toxicity of dichlorvos on common carps was studied through short term static bioassay tests. The doses for the definitive tests were selected on the basis of predetermined range finding tests run in triplicates. the definitive test was also repeated thrice for accuracy in the results. The 96-h LC₅₀ value of dichlorvos for Cyprinus carpio var. communis was found 2.56 ppm by probit analysis. The mean values of water quality in aquarium didn’t indicate marked variation confirming mortality of fishes due to pesticide toxicity and not hypoxia. Fishes exhibited behavioural responses like erratic movements, convulsions, imbalanced swimming which ended in a collapse to the bottom of the aquarium and increase in respiratory motions during the entire period of the bioassay. Before death, the clinical signs like fainting of body color, gulping onto air-water interface in aquaria and in extreme cases, the hemorrhagic patches on selected sites of skin were noticed with the termination of the experiments. The results suggested that dichlorvos is potentially toxic to fishes and its entry into natural waterbodies must be checked or otherwise it can prove harmful to fishes and human beings as well through the food chain.