The acute toxicity of Phenol to the Nile Tilapia Oreochromis niloticus fingerlings were assessed in a semi static bioassay for 96 hours. Six gradual concentrations of Phenol were prepared as follows: 5, 15, and 25, 35, 45, 55 mg/L and a control experiment (0 mg/L). At various concentration of phenol, fish showed uncoordinated behavior such as gulping of air, attempts to escape from the pollutant, collapse of fish on their sides cease of opercular movement (death). The 24,48,72and 96 hours LC50 (the concentration that kills half of the population ) computed were 26.3 ,24.9 ,23.8 and 22.3 mg/L respectively. The median LT50(time taken to kill half of the population ) calculated were 434, 46, 6 and 2 hours for concentrations 15, 25, 35 and 45 mg/L, respectively. No mortality was observed at concentration 5 mg/L. Other concentrations showed increasing mortalities with increase in exposure time. The Predicted threshold concentration of phenol was found to be 1.12 mg/L. Results obtained revealed that Phenol is highly toxic to the Tilapia Oreochromis niloticus fingerlings.
Key words: Phenol, acute toxicity, Oreochromis niloticus ,LC50 ,LT50 .