Acute toxicity of refined oil on the catfish, Clarias gariepinus (Teugels, 1984) (Pisces: Clariidae)

Laboratory static bioassays were conducted to determine the 24-, 48-, and 96 -hour LC50 and the lethal levels of concentrations of oil-in-water dispersions (OWD) of used and fresh fuel oil for embryo, fry and fingerlings of the catfish Clarias gariepinus(Teugels, 1984). The most sensitive was the embryonic stage while the fingerlings were most resilient. The LC50 values obtained for treatment with fresh fuel oil were as follows: Embryos (24- and 48 -hour LC50) 0.034 ml/l and 0.042 ml/l respectively. For the fry (24-, 48-, 72- and 96-hour) the LC50 values were 1.22ml/l, 0.85ml/l, 0.83ml/l and 0.70ml/l respectively. The fingerlings had 48-, 72 and 96-hour LC50 values of 5.00 ml/l, 2.30 ml/l and l.78ml/l respectively. The LC50 values for treatment with used fuel oil were as follows: Embryos (24 - and 48 -hour LC50) 0.032 ml/l and 0.04 ml/l respectively. For the fry (24-, 48-, 72-and 96-hour LC50) values were 1.59 ml/l, 1.14 ml/l, and 1.12 ml/1 while the fingerlings had 0.82 ml/l, 1 .37 ml/l and 1.02 ml/l as their 48-, 72- and 96-hour LC50 values respectively. Loss of skin pigmentation was observed in fish exposed to fresh fuel oil and darker pigmentation in fish exposed to used oil. Activity generally decreased with increased concentration of toxicant and longer duration of exposure. A similar trend was observed for hatchability of the embryos. Increased mouth and opercular breathing were also observed. Tropical Freshwater Biology VOL. 8 1999, pp. 17-26 KEY WORDS: Petroleum-Refined Oil-Toxicity-Behaviour-Clarias gariepinus, Nigeria