MORPHOLOGICAL ABNORMALITIES IN AFRICAN CATFISH (CLARIAS-GARIEPINUS) LARVAE EXPOSED TO MALATHION

Newly hatched larvae of Clarias gariepinus were exposed to malathion c oncentrations ranging from 0.3 mg/l to 5.0 mg/l. Their development was observed through five days posthatch, i.e. the stage in which the ver tebral elements are not yet present and the notochord is the only func tional body axis. A significant higher proportion of C. gariepinus lar vae with deformed notochord and pericardial edema was detected at 2.5 mg/l malathion and higher. The results suggested that (1) deformed not ochord was the result of the uncontrolled contractions of the body mus culature due to malathion toxicity and (2) the vertebral deformities o bserved in the fish which have been exposed to malathion from the noto chord-stage onwards were the result of a deformed notochord instead of the deformation of the vertebral elements themselves. (C) 1997 Elsevi er Science Ltd.