Two assays were carried out to evaluate Oreochromis niloticus sensitivity to different herbicides. In the first experiment, atrazin concentrations (0; 2.5; 5; 10 and 20 mg L-1) were evaluated aiming to determine lethal concentration (LC50) to O. niloticus. In the second assay, the effects of the herbicide mixtures alachlor + atrazin (5.33 + 5.33 mg L-1), diuron + MSMA (5.33 + 2.13 mg L-1 ), paraquat (1.33 mg L-1 ) and 2,4-D + picloran (1.28 + 0.34 mg L-1 ), were evaluated on O. niloticus survival after 96 h of exposure. In the first assay, a sharp decrease in fingerlings survival was observed from 3 mg L-1 of atrazin with CL50 value of 5.02 mg L-1 and a high biomass decrease due to herbicide presence. In the second assay, a greater negative effect was observed on fingerlings by alachlor + atrazin. . After 72 h of incubation, intoxication rate showed a reduction in the number of individuals of 17.4% for paraquat, 2,4 D + picloram and diuron + MSMA, and of 100% for alachlor + atrazin. It was concluded that CL50 obtained for atrazin is inferior to that listed as toxic to trouts and that the alachlor + atrazin mixture can be characterized as a risk to O. niloticus, even when applied at commercially recommended rates.
alachlor; atrazin; 2,4-D; diuron; paraquat; picloram
