Morphological abnormalities in african catfish (Clarias Garieupinus) larvae exposed to malathion

Newly hatched larvae of Clarias gariepinus were exposed to malathion concentrations ranging from 0.3 mg/I to 5.0 mg/I. Their development was observed through five days posthatch, i.e. the stage in which the vertebral elements are not yet present and the notochord is the only functional body axis. A significant higher proportion of C. gariepinus larvae with deformed notochord and pericardial edema was detected at 2.5 mg/l malathion and higher. The results suggested that (1) deformed notochord was the result of the uncontrolled contractions of the body musculature due to malathion toxicity and (2) the vertebral deformities observed in the fish which have been exposed to malathion from the notochord-stage onwards were the result of a deformed notochord instead of the deformation of the vertebral elements themselves.