EVALUATION OF ACUTE TOXICITY OF DICHLORVOS (NUVAN) TO FRESHWATER FISH, OREOCHROMIS MOSSAMBICUS (W. K. H. PETERS, 1852) AND THEIR ETHOLOGICAL CHANGES

The present study was done to evaluate the acute toxicity of Dichlorvos (Nuvan) to freshwater fish, Oreochromis mossambicus. The 24, 48, 72 and 96 h LC50 values of Dichlorvos to Oreochromis mossambicus were 3.84, 3.50, 3.12 and 2.90 mg/l respectively. The mortality rate of the fish varied significantly (p<0.05) over the control at all the treatments of Dichlorvos irrespective of exposure times. The mortality rate of the fish also varied significantly (p<0.05) at all the exposure times (24, 48 and 72 and 96h) at 2.6 mg/l of toxicant and above. The fish showed excess mucous secretion and frequent vertical hanging posture at higher concentrations during 72 and 96h of exposure. The hyper-excitability of fish was also recorded at higher concentrations during 24h of exposure. The opercular movement of treated fish was increased significantly (p<0.05) over the control with the increasing concentrations of toxicant.