Inhibition, recovery and field responses of Astyanax fasciatus (Cuvier, 1819) brain cholinesterases upon exposure to azinphos-methyl

Pesticides used in agriculture are among the most important environmental pollutants. Organophosphate and carbamate insecticides, intensely used in deciduous fruit-trees, may be  transported to aquatic ecosystems by runoff. Northwest rural Montevideo possesses zones of fruit-tree farms, where azinphos-methyl is currently the most used pesticide. Despite the well-known neurotoxic properties of this agrochemical, studies of its effects on aquatic organisms are scarce in Uruguay. The main goal of this study was to evaluate effects on brain cholinesterases and erythrocyte micronuclei in Astyanax fasciatus exposed to azynphos-methyl in laboratory and field conditions. Dose-response curves showed concentration-dependent brain cholinesterase inhibitions and a LC50 (48-hour) of 2.31 mg L -1 for azinphos-methyl.  Fishes exposed for 48 hours to toxicant and then transferred to clear water recovered 80% of brain cholinesterase activity in 10 days. Field study indicated that A. fasciatus from a watershed with low contamination showed a brain cholinesterase specific activity of 62.2±5.1 Units.mg -1 protein (22oC) 97.7 % of which was acetylcholinesterase. Specimens from a basin with intense fruticulture exhibited a spatial gradient: specimens collected downstream to the farms showed brain acetylcholinesterase activities 32% lower than fishes captured upstream. In conclusion, our data suggest that A. fasciatus is a suitable species for exotoxicological biomonitoring. Keywords : Acetylcholinesterase; Astyanax fasciatus; Aquatic Biomonitoring; A zinphos-methyl; Bioindicator; Brain cholinesterases; Fish; Organophosphate pesticide.