Sublethal adverse effects may result from exposure of aquatic organisms to insecticides at environmentally relevant concentrations. Fingerlings of the common carp (Cyprinus carpio, Linnaeus, 1758), grass carp (Ctenopharyngodon idella, Valenciennes, 1844), and bighead carp (Aristichthys nobilis, Richardson, 1845) were exposed to diafuran, an insecticide widely used during rice cultivation in Southern Brazil. The aim of this study was to verify the relationship between the lethal concentration (LC50) of diafuran and the acetylcholinesterase (AChE) activity in brain and muscle tissues of these species as a possible early biomarker of exposure to this insecticide. LC50 was determined for fish exposed to diafuran concentrations during 96 h (short term): common carp: control, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mg L-1; grass carp: control, 1.0, 2.0, 3.0 and 3.5 mg L-1 and, bighead carp: control, 0.5, 1.0, 1.5, 2.0, 3.0 and 4.0 mg L-1, as well as the determination of AChE at concentrations near LC50 for these species. LC50 values (nominal concentrations) were 1.81 mg L-1 for the common carp, 2.71 mg L-1 for the grass carp and, 2.37 mg L-1 for the bighead carp. All carps exposed to diafuran were lethargic (lower concentrations) or immobile. Diafuran inhibited the acetylcholinesterase activity in brain (~38%) and muscle (~50%) of all species. Muscle of bighead carp under control treatment showed higher specific AChE activity than brain (14.44 against 5.94 µmol min-1 g protein-1, respectively). Concentrations of diafuran used for rice cropping may affect Cyprinus carpio, Ctenopharyngodon idella and Aristichthys nobilis behaviors and the AChE activities in brain and muscle of these species may be an early biomarker of toxicity of this insecticide.
Cyprinus carpio; Ctenopharyngodon idella; Aristichthys nobilis; pesticide; lethal concentration
