Sub-lethal concentrations of monocrotophos affect aggressive behavior of the fishes Astyanax altiparanae Garutti & Britski (Teleostei, Characidae) and Oreochromis niloticus (Linnaeus) (Teleostei, Cichlidae)

This study investigated the effects of sublethal concentrations of the pesticide monocrotophos (organophosphate) on the agonistic behavior of two fishes species, Astyanax altiparanae Garutti & Britski, 2000 (lambari) and Oreochromis niloticus (Linnaeus, 1758) (Nile tilapia). Sublethal concentrations of the pesticide for the two species were determined and lambari was more resistant than Nile tilapia. The sublethal concentrations were smaller than 400 mgl super(-1) for lambari and 20 mgl super(-1) for Nile tilapia. The two species were tested in grouping conditions (triads) and isolation, under monocrotophos concentrations of 200 mgl super(-1) for lambari and 5 mgl super(-1) for Nile tilapia. The concentration decreased the aggressiveness in lambari, but in Nile tilapia an opposite effect was detected. The results show a species-specific effect of the monocrotophos on aggression.