Effects of paraquat (Osaquat® formulation) on survival and total cholinesterase activity in male and female adults of Cnesterodon decemmaculatus (Pisces, Poeciliidae)

Ecotoxicity assessment of the herbicide paraquat was carried out with adults of a native freshwater fish Cnesterodon decemmaculatus. The acute toxicity of paraquat was evaluated and the enzymatic activity of the total cholinesterases was measured using sublethal concentrations of the herbicide. Experiments were designed to separate the responses between sexes. In the study, paraquat was added as a commercial formulation Osaquat(R) containing 27.6% of active ingredient. The 96-h LC50 values for males and females were 67.40- and 52.48-mg of paraquat per liter, respectively. This significant, but close difference between sexes changes when we compare acute toxicity data between adults and fry of Cnesterodon decemmaculatus. The 96-h LC50 for the latter is 9.41-mg of paraquat per liter and the adult/fry ratio approaches 1 order of magnitude. Sublethal concentrations of paraquat (the higher of these was 20 mg/L) did not produce inhibition of the total cholinesterase activity for males and females compared to the controls at 96 h of exposure. On the other hand, we found a significant difference between sexes (p less than or equal to 0.05): about 50% for the enzymatic activity measured. Thus, our results indicate that total cholinesterase activity of Cnesterodon decemmaculatus is sex dependent. (C) 1998 by John Wiley & Sons, Inc.