Author(s): Akin-Obasola BJ

Abstract: Range finding, Acute and sub-lethal toxicity test of a 3:2 mixture of petrol and engine oil on the African catfish, Clarias gariepinus fingerlings (0.83±1.23g) using 96-hour bioassay was carried out. Range finding test using ten (10) concentrations of 0.50, 0.67, 0.83, 1.00, 1.67, 1.83, 2.00, 217 and 3.33 ppt; was carried out to determine the definitive concentration. The acute test determined graphically revealed lethal median concentration (LC₅₀) of 2.06 ppt and the safe concentration of 2.0 ppt. Mortality was higher within the first 24hrs and increased with increase in concentration of the toxicant. Significant differences (p<0.05) in mortality occurred between the various concentrates (2.00, 2.07, 2.14, 2.21, 2.28 ppt) used in the acute test. Clarias gariepinus fingerlings exposed to sub-lethal test with concentrations 0.83, 0.90, 0.97, 1.04 and 1.11 ppt had 0, 40, 50 and 100% mortality within 14 days of experiment. Fish also showed abnormal behaviour, examples are; restlessness, sudden quick movement, erratic swimming pattern, loss of reflex and discolouration. Histopathological changes in gills and skin of the catfish showed alteration of the gill and separation of the epithelial layer from the supportive tissue respectively. Water quality was poor in treatments with higher concentrations as 96-hour bioassay days progresses, specifically, dissolved oxygen greatly reduced in value within the 96 hours bioassay.

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