Fipronil-based insecticide induces developmental toxicity and skeletal deformities in zebrafish (Danio rerio)

The Fipronil (FIP), a member of the phenylpyrazole family, is a second-generation insecticide that is highly active, broad-spectrum, and has multiple applications in agriculture and veterinary applications for pest and vector control. However, the mechanism of action and the hazardous effects of FIP-based commercial formulations on the early developmental stages of fish, particularly in the skeletal system, remain poorly understood. Therefore, the present study aimed to investigate the ecotoxicological effects of a FIP-based commercial formulation on the development of the zebrafish (Danio rerio), using a multi-biomarker approach with a primary focus on skeletal developmental toxicity. Zebrafish embryos were exposed to environmentally relevant concentrations of FIP (5, 10, 25, 50, and 100 µg L⁻¹) for 168 hours, along with negative, solvent, and positive control groups, in semi-static exposure. Endpoints evaluated included mortality, hatching rate, neurotoxicity, cardiotoxicity, morphological alterations, biometric parameters and cartilaginous, and bone alterations. The results demonstrated that FIP-based commercial formulation induced high mortality, reduced hatching success, promoted neurotoxicity, cardiotoxicity, and significant morphological, biometric, and skeletal abnormalities, including reduced size, morphological abnormalities, and the absence of skeletal structure formation even at low concentrations in zebrafish embryos and larvae. Overall, the current study demonstrated the effects of FIP-based commercial formulation on skeletal development in fish, indicating their potential ecotoxicological impact on aquatic vertebrates.