Morphological, histological and multi-omics analysis revealed the molecular response of female western mosquitofish (Gambusia affinis) to levonorgestrel exposure.

In recent years, the use of synthetic progestogens in medicine has increased, and their presence is frequently detected in rivers. Therefore, an increasing number of researchers are beginning to focus on the impact they have on the reproduction and development of aquatic organisms. Levonorgestrel (LNG) is a synthetic progestin widely used in oral contraceptives and is also frequently detected in rivers. To assess the impact of LNG on mosquitofish (Gambusia affinis), in this study, adult female mosquitofish were exposed to LNG at concentrations of 0, 5, 50, and 500 ng/L for 36 consecutive days, followed by morphological, histological, hepatic transcriptomic and metabolomic analyses. The results indicated that exposure to LNG reduced the weight-to-length ratio of mosquitofish and simultaneously elongated their anal fins. Furthermore, at a concentration of 500 ng/L, the gonadal index and the proportion of late-stage oocytes in mosquitofish were significantly reduced, and the transcriptional expression of the genes Cyp19a1a, Cyp11a1a, Ara, and Foxl2 was markedly inhibited. Additionally, exposure to LNG led to hepatocyte degeneration and vacuolation. Transcriptomic and metabolomic analyses of the liver identified a large number of differentially expressed genes and metabolites, which were enriched in many metabolism-related pathways, such as the Insulin signaling pathway, Biosynthesis of amino acids, and Fatty acid metabolism. In summary, these results indicated that exposure to LNG could suppress ovarian development in female mosquitofish, leading to masculinization, and caused abnormalities in liver transcription and metabolism.