Ancestral osmotic stress exposure alters offspring transcriptomic responses to acute hypotonic challenge in marine medaka

Environmental salinity instability associated with climate change increasingly challenges aquatic organisms inhabiting marine and estuarine ecosystems. Although osmotic acclimation mechanisms in euryhaline fish have been extensively investigated, whether ancestral osmotic stress exposure alters offspring osmotic responsiveness remains poorly understood. In the present study, marine medaka (Oryzias melastigma) derived from osmotic stress-experienced (EXP) and non-experienced (Non-Exp) F2 lineages were subjected to acute hypotonic challenge before gill RNA-sequencing analysis. Acute hypotonic exposure induced broader transcriptomic remodeling in the Non-Exp lineage, whereas the Exp lineage exhibited a smaller but more condensed enrichment profile associated with osmosensing- and ion transport-related pathways. The Non-Exp lineage predominantly enriched pathways related to RNA transcription, membrane trafficking, epithelial remodeling, and stress-associated signaling. In contrast, the Exp lineage preferentially enriched pathways associated with TRP channels, stimuli-sensing channels, ion channel transport, and SLC-mediated transmembrane transport. Representative osmoregulatory transcripts including trpv4, aqp3, and slc12a1 were additionally altered in the Exp lineage. Collectively, these findings suggest that ancestral osmotic stress exposure may influence offspring transcriptomic responses to acute hypotonic challenge and provide evidence for transgenerational plasticity in osmotic acclimation.