Sex-specific divergent responses of marine medaka (Oryzias melastigma) towards long-term benzo[a]pyrene exposure revealed stronger resilience and recoverability in female fish.

Benzo[a]pyrene (BaP), a representative five-membered polycyclic aromatic hydrocarbon, has been extensively studied as a pollutant for decades. Despite this, sex-specific responses to BaP exposure remain poorly understood. This study employed a life-cycle exposure approach to investigate the effects of prolonged BaP exposure on marine medaka (Oryzias melastigma), highlighting sex-specific responses. After a 90-day exposure period, significant variations in biometric measurements and oxidative stress markers were observed between male and female fish. BaP exposure resulted in weak detoxification defense in males, while females exhibited an opposite response. Transcriptomic analysis revealed 13 significantly enriched pathways in males and 11 in females, with varying numbers of differentially expressed genes between the sexes, highlighting distinct biological responses. Host resistance assay showed higher mortality rates among BaP-exposed males, and suppressed immune gene expressions and lysozyme activity, while females demonstrated enhanced immune genes and lysozyme activity post-challenge, indicating a more resilient defense response. Furthermore, after a one-month depuration period following BaP exposure, male medaka demonstrated slower recoverability compared to females. These findings underscore sex-specific effects of BaP exposure on fish, with females displaying stronger resilience. Understanding these distinctions are crucial for accurately assessing the impact of environmental pollutants on the aquatic population and ecosystem maintenance.