Influence of low concentrations of Trichlorfon on haematological parameters and brain acetylcholinesterase activity in common carp, Cyprinus carpio L.

Trichlorfon, an organophosphorus insecticide, is used in aquaculture to eliminate fish ectoparasites. The present study was aimed at evaluating the effects of low concentrations of Trichlorfon (0.25 and 0.50 mg L-1 for 1 and 24 h) on selected haematological parameters and brain acetylcholinesterase (AChE) of subadults of common carp, Cyprinus carpio. Results showed that Trichlorfon had no significant effect on the survival and haematocrit values of the exposed fish. However, all fish exposed to Trichlorfon exhibited leucopenia coupled with lymphocytopenia. Upon transfer to clean water, leucopenia did not return to normal in seven days. Brain AChE activity of the fish exposed to Trichlorfon for 24 h was reduced by 55-57% compared with the controls and inhibition was not restored fully within seven days. Hence, precautions should be taken when even low concentrations of Trichlorfon are used in carp culture, especially for long-term treatments.