Multibiomarkers approach to assess the acute toxicity of chlorantraniliprole in <i>Cnesterodon decemmaculatus</i> (Jenyns, 1842) (Cyprinodontiformes: Poeciliidae)

Chlorantraniliprole (CHL) is the most widely used diamide worldwide, with South America being its primary market. Despite its growing application, the environmental effects of CHL on nontarget organisms, mainly native fish species, remain understudied. In this study, the sublethal effects of CHL were assessed in Cnesterodon decemmaculatus by acute exposure (96 hr) to 1/10 (1.5 mg/L) and 1/100 (0.15 mg/L) of the median lethal concentration, using a multi-biomarker approach across different levels of biological organization. Locomotor activity (distance traveled, time immobile, average, and maximum speeds), somatic index, enzymatic activities of acetyl-cholinesterase (AChE) in muscle and brain, catalase (CAT) in muscle, brain, gills, and liver, glutathione-S-transferase (GST) in gills and liver, aspartate amino-transferase (AST), alanine amino-transferase (ALT), AST to ALT ratio, and alkaline phosphatase in the liver were measured. The primary effect of exposure was the reduction in locomotor activity, which appears to be more closely related to CHL's mode of action than cholinergic effects. The muscles and brain were the organs most affected by oxidative stress, and adaptive responses involving AChE, CAT, and GST were observed, highlighting the organism's ability to manage oxidative stress. The Integrated Biomarker Response (IBR) index indicates a dose-dependent relationship, with individuals exposed to T2 exhibiting more than twice the IBR value of those exposed to T1 and nearly four times that of the control group. Our results indicate that insect-specific compounds like diamides can severely affect nontarget species, potentially affecting survival and growth rates in aquatic species, even at sublethal concentrations. For muscle-targeted insecticides, locomotor activity is one of the most effective biomarkers for assessing the impact of exposure. This study represents the first report on the toxicity of a diamide in a native South American model fish, a key bioindicator in assessing ecological health.