Acute toxicity and behavioural responses in Clarias batrachus (Linnaeus) exposed to herbicide pretilachlor

Pretilachlor is a systemic herbicide belonging to chloroacetamide group which is being used in rice fields for the control of annual weeds. The acute toxicity bioassay of pretilachlor was carried out by probit analysis method and the safe level was estimated by multiplying the 96 h LC(50) with different application factors. The 12, 24, 48, 72 and 96 h LC(50) values were obtained as 11.12, 9.55, 8.57, 7.11 and 5.84 mg L(–1) respectively while the safe values found ranges 0.05 to 0.58 mg L(–1). Buccal movements as well as the number of burst swimming movements in fishes exposed to pretilachlor were found to be increased significantly in response to all concentrations of the herbicides tested. Number of feeding attempts reduced significantly while irregular responses in fishes were observed regarding their attempt to form group after exposure to herbicide. As a whole, exposure of fishes to pretilachlor showed significant effects on all studied behaviours. So it can be concluded that the herbicide pretilachlor is toxic to fishes and its excess use should be avoided.