Short-term parental exposure to diazepam disrupts development, behavior, and transcriptional profiles in zebrafish offspring.

Diazepam (DZP) is a pervasive emerging contaminant known to induce significant sublethal adverse effects in aquatic species. However, the intergenerational impacts of parental DZP exposure on fish offspring remain poorly understood. In this study, we exposed zebrafish (F0) to DZP at 8 μg/L for 7 days and investigated variation in the development, behavior, and transcriptional profiles of their offspring (F1) reared in DZP-free medium. The results suggest that DZP accumulates in F0 ovaries and is vertically transmitted to F1 embryos, resulting in-ovo exposure. The parental DZP exposure significantly increased F1 embryo mortality and accelerated their hatching. Moreover, parentally DZP-exposed F1 larvae exhibited reduced locomotor activity and increased exploratory behavior. Transcriptomic analysis identified 404 differentially expressed genes, which were significantly enriched in KEGG pathways related to metabolism and organismal systems. In parentally DZP-exposed F1 larvae, transcriptional responses in the pathways of xenobiotic biodegradation and metabolism were driven primarily by key genes encoding detoxification enzymes, and the activation of lipid metabolism pathways was underpinned by the up-regulated expression of vital apolipoprotein-encoding genes. Conversely, circadian rhythm suppression was characterized by coordinated downregulation of clock and cryptochrome genes. Overall, these findings provide preliminary insights into the intergenerational toxicity induced by parental DZP exposure, offering potential molecular clues for future studies on its ecotoxicological effects on the fish population.