This study was planned to study the impact of effluent discharged from one International Paper Industry, located at the outskirt of Rajmundry (A.P.) on the bank of river Godavari on the toxicity and behaviour of a fresh water fish, Oreochromis mossambicus, Peters (Tilapia) under laboratory controlled conditions. Fishes were exposed to graded series of concentrations of the effluent for acute toxicity studies. The MAC value deduced was 3.45% of effluent in 50 liters of water for 30th days. A safety concentration of 3.4% of effluent l-50 was selected for this study. Significant amount of mercury and cadmium was available in the effluent of the paper mill. Exposed fishes appeared lethargic after 7th days of exposure, when compared to the control fish. Significant decrease in body weight was marked in the effluent exposed fish when compared to control fish. The body weight of the effluent exposed significantly declined with the increase in exposure period. No recovery in body weight was noticed when the exposed fishes were transferred to toxicant free medium. The BSI and LSI was significantly affected in the effluent exposed fish when compared to control fish. The impact was not severe in case of BSI at initial period of exposure. However, with the increase in exposure period the BSI was significantly damaged. The liver was affected from the very beginning of the exposure. Maximum depletion in LSI was noted on 28d of exposure. No recovery was marked in case of LSI during recovery studies.