The effect of liquid petroleum refinery effluent on fingerlings of Sarotherodon melanotheron (Ruppel 1852) and Oreochromis niloticus (Linnaeus 1757)
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The toxicity of petroleum refinery effluent from Alesa-Eleme (Port Harcourt) Refinery, to two tilapia species, Oreochromis niloticus and Sarotherodon melanotheron, fresh and brackish water species respectively were investigated at an average temperature of 27°C ± 2.5°C under laboratory conditions. LT50 values increased from 29' minutes at 100% effluent concentration to 645 minutes at 10% effluent concentration (Vol/Vol) for O. niloticus and from 48 minutes at 100% to 1,917 minutes at 10% for S. melanotheron. Toxicity of effluent to fish decreased as the effluent aged. LT50 for 2-day and 6-day old effluent for O. niloticus at 63.1% effluent concentration were 30 and 70 minutes respectively. Median lethal concentrations (LC50) obtained from regressions of effluent concentrations and median lethal times (LT50) for 6-day old effluent at 24, 48 and 96 hours were 5.6, 3.29 and 1.93 percent respectively for O. niloticus, while the corresponding values for S. melanotheron were 9.48, 5.83 and 3.6% respectively. The safe concentrations of 6 and 15-day old effluents were estimated as 0.19 and 0.29% respectively for O. niloticus, while the corresponding values were 0.36 and 0.35 for S. melanotheron. The 24 and 48 hours LC50 values show that S. melanotheron is more resistant to oil refinery effluent than O. niloticus.