Reproductive toxicity of chronic exposure to cortisone in western mosquitofish (Gambusia affinis)

Cortisone is a commonly found in a variety of aquatic environments and has potential adverse effects on aquatic organisms. This study was to assess the chronic toxic effects of cortisone at different concentrations (0.0, 5.0, 50.0 and 500.0 ng/L) for 60 days on adult female western mosquitofish (Gambusia affinis). The results revealed that cortisone significantly increased the proportion of perinuclear oocytes concomitant with reduced the prevalence of late-stage oocytes, indicating arrested oocyte maturation. Meanwhile, exposed females exhibited compromised mate attraction and diminished courtship interactions. Transcriptomic profiling of the ovaries identified significant enrichment of steroidogenic pathways (p < 0.001), with the differentially expressed gene CYP21A2 demonstrating pronounced up-regulation relative to that of the control fish. Gene expression and plasma steroid analyses further showed decreased expression of key genes in the hypothalamic-pituitary-gonadal (HPG) (lhb, fshb, gnrh2, gnrh3, and cyp19a1b in the brain; cyp19a1a and hsd20b in the ovary), whereas ovarian star, cyp17, hsd3b, and hsd17b3 were up-regulated. This transcriptional dysregulation disrupted plasma steroid homeostasis, manifested by significantly decreased levels of estradiol and 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DHP), contrasted with a pronounced increase in 11-ketotestosterone. Vitellogenin gene transcription was also suppressed in both liver and brain tissues. Collectively, cortisone exposure induced endocrine disruption in G. affinis, which may ultimately compromise population stability. These findings provided valuable information for further understanding the potential ecological risks of corticosteroids.