Abstract
Fish and other organisms are affected by pesticides which pollute the natural water through agricultural runoff. Fishes are common bio-indicators of water pollution. In the present study bioassay of organophosphate pesticide, Phorate was done on Oncorhynchus mykiss. Data obtained from the toxicity tests were evaluated using the Probit Analysis Statistical Method. The 96h LC50 of phorate was found to be 19.81ppm respectively. The fish exhibited erratic swimming, copious mucus secretion, loss of equilibrium and hitting to the walls of test tank prior to mortality. Keywords: Phorate, Oncorhynchus mykiss, Toxicity and 96h LC50