Abstract:
Different concentration of pyrethroid pesticide Cypermethrin (0, 50, 75, 100, 125 and 150 ppb) was exposed to 35-40 gm sized tilapia (Oreochromis niloticus). After a 96 hr static bath exposure, a median lethal concentration (LC50) was determined by an application of Probit test. Degree of cypermethrin toxicity depended on the exposure concentration, with a median lethal concentration of 59.41 ppb. Fish exposed to 50 ppb of cypermethrin showed stress sign with dark coloration, but possessed normal movement. Fish exposed to higher concentration showed abnormal movement, indicating cholinergic overload, or death, depending on the dose. Subacute toxicity study, approached by an exposure to 7.5, 15 and 30 ppb of cypermethrin for 30 days, revealed no death or abnormality of the exposed fish. Histological lesions of gill, spleen and blood morphology did not correlate with the exposed concentration. Serial measurements of cholinesterase activity in serum sampled on 15 and 30 days post exposure presented a significant reduction (p< 0.05). From the results, tilapia appears to be more tolerant to pyrethroid pesticide than many other aquatic animals have been reported. The result supports the application of cholinesterase activity assay for detection of pesticide exposure, particularly when a field population exposed to low concentration of pyrethroid pesticide, as low as 7.5 ppb. The experiment also indicates that nondestructive, serial measurements of cholinesterase activity are valuable biomarkers of pesticide contamination in living inhabitants.