Effects of Exposure to Diazepam on the Survival, Development, Behavior, and Transcriptomic Profiles in the Offspring of Japanese Medaka

Diazepam (DZP), an emerging medicinal pollutant routinely identified in aquatic ecosystems, has been shown to accumulate significantly in the gonads of fish species. Nevertheless, the detrimental impacts stemming from parental DZP exposure on fish offspring remain insufficiently characterized. This study examined the effect of 4–week DZP exposure (0.8 μg/L) in F0 generation Japanese medaka on the survival capacity, ontogenetic development, behavioral responses, and transcriptional regulation of their offspring (F1 generation). Following over two weeks of exposure, F0 individuals exhibited a marked decline in daily egg production. Parental exposure can transmit DZP to offspring of Japanese medaka and significantly reduce the survival and hatching rates of F1 individuals. In the light/dark transition test, F1 larvae derived from DZP–exposed parents demonstrated lower average swimming velocity. Furthermore, transcriptome analysis identified 341 differentially expressed genes (DEGs, 261 up–regulated, and 80 down–regulated) in F1 larvae of DZP–exposed parents. Those DEGs are enriched within three critical KEGG pathways: Antigen processing and presentation, Endoplasmic reticulum protein processing, and Estrogen signaling pathway. Considering that residual DZP levels detected in aquatic ecosystems may exceed the experimental threshold (0.8 μg/L), the impacts of parental pharmaceutical exposure on fish offspring should be of greater concern.