Abstract: The continuous discharge of petroleum hydrocarbons, oil spills and gas flaring have led to extensive degradation of aquatic ecosystems, destruction of mangrove swamps and loss of biodiversity. The acute toxicity of light and heavy crude oils to fingerlings of the catfish, C. gariepinus (mean total length, 15.40+0.57 cm, mean weight, 22.08+2.51 g) were studied in static toxicity bioassay over a 96-hr period after acclimation of test organisms in the laboratory. There were initial range finding tests to determine the concentrations of the toxicants to be administered on the test organisms in the definitive tests. The test organisms were exposed to five concentrations (1.0, 1.5, 2.0, 2.5 and 3.0%) of both toxicants and a control (0.0%) in static renewal bioassay. The median lethal time (LT50) at concentrations of 2.0, 2.5 and 3.0% were 2.75 hrs, 1.67 hrs and 1.17 hrs respectively for the light crude oil while that of heavy crude oil at concentrations of 2.5 and 3.0% were 45.00 hrs and 36.00 hrs respectively. Mortalities increased with increase in both crude oils concentrations. The 96-hr median lethal concentrations (LC50) for light and heavy crude oils were 1.4% (14 ml/l) and 2.2% (22 ml/l) respectively. The dissolved oxygen levels, pH and temperature values of the control were higher than those of the treated group. Results showed that light crude oil was more toxic than heavy crude oil.
Key Words: Toxicity, bioassay, light crude oil, heavy crude oil, median lethal time (LT50), median lethal concentration (LC50).jaerem NEW Sado O. M 2A
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