Developmental and systemic toxicity of the triazole fungicide tetraconazole in zebrafish: Integrated evidence from ER stress, apoptosis, and metabolomic disruption.

Tetraconazole is a chiral triazole fungicide widely used in modern agriculture to control fungal diseases in cereal crops and horticultural products. Due to its extensive application and environmental persistence, tetraconazole can enter aquatic ecosystems via agricultural runoff, raising concerns about its potential effects on non-target aquatic organisms. In this study, the developmental, physiological, molecular, and metabolomic toxicity of tetraconazole was evaluated using zebrafish (Danio rerio) embryos, larvae, and adults as a vertebrate model. Zebrafish embryos were exposed to tetraconazole for 96 h to assess embryonic mortality, hatching success, heart rate, morphometric parameters, and developmental malformations. In parallel, adult zebrafish were subjected to a 14-day sub-chronic exposure to evaluate physiological condition indices, including body mass index (BMI), condition factor (CF), and hepatosomatic index (HSI). To elucidate underlying toxicity mechanisms, the expressions of endoplasmic reticulum (ER) stress-related genes (PERK, IRE1, and ATF6) and apoptosis-associated genes (Caspase-3, Caspase-9, Bax, and Bcl-2) were analysed in larvae as well as in adult brain and liver tissues. Untargeted metabolomic profiling using Q-TOF MS/MS and multivariate chemometric analyses was performed to identify tissue-specific metabolic alterations. Tetraconazole exposure induced concentration-dependent embryonic mortality, delayed hatching, reduced heart rate, growth inhibition, and severe morphological abnormalities, including spinal deformities and pericardial edema. In adult zebrafish, significant changes in BMI and HSI indicated disrupted energy balance and hepatic stress. Molecular analyses revealed activation of ER stress signaling and apoptosis, particularly in liver and brain tissues, while metabolomic results demonstrated pronounced disturbances in amino acid, lipid, and energy metabolism. Overall, these findings indicate that tetraconazole poses a significant toxicological risk to aquatic vertebrates by disrupting early development, inducing ER stress-mediated apoptosis, and altering metabolic homeostasis, highlighting the need for improved ecological risk assessment strategies.