Experimental exposure of African catfish Clarias Gariepinus (Burchell, 1822) to phenol: Clinical evaluation, tissue alterations and residue assessment

There is lack of information regarding; the toxicological and pathological consequences of phenol stressed Clarias gariepinus; as well as; the susceptibility of the stressed fish to disease occurrence. Static renewal bioassay was experimentally conducted to evaluate the toxic effects of phenol on the African catfish C. gariepinus. Ninety-six-hour acute toxicity tests revealed that the median lethal concentration of phenol (LC50) is 35 mg/L by immersion. Four experimental fish groups were assigned for 3 weeks exposure test; three were exposed 20%, 50% and 70% LC50, the fourth control fish group received a vehicle of dechlorinated water. Abnormal signs including cessation of feeding, nervous manifestations; skin expressed perfuses mucous, black patches with skin erosion and ulcerations in the later stages. All observations were correlated to the time and dose of exposure. Post mortem examination revealed adhesion of the internal organs. For tissue alterations; Skin, gills, brain, liver and kidney showed variable degrees of degenerative changes and necrosis. Muscle residues shown in mean ± SE were 4.3 ± 0.05 and 6.65 ± 0.05 ppm in groups that received 20 and 50% LD50, respectively. Infection with Aeromonas hydrophila resulted in high percent of mortalities with a non significant difference between the challenged fish groups. The study cleared that phenol is toxic to C. gariepinus under experimental conditions.