Effects of steroid hormones and their mixtures on western mosquitofish (Gambusia affinis)

Steroid hormones, including estrone (E1), androstadienedione (ADD), and androstenedione (AED), are prevalent in aquatic ecosystems and pose ecological risks due to their disruptive influence on fish populations. However, little consideration has been given to the endocrine disrupting effects of fish exposed to complex mixtures of hormones in the real world. In this study, adult female western mosquitofish (Gambusia affinis) were exposed to two concentrations of E1 (100 ng/L for E1L and 5,000 ng/L for E1H), ADD (100 ng/L for ADDL and 10,000 ng/L for ADDH), and AED (100 ng/L for AEDL and 10,000 ng/L for AEDH) as well as four binary mixture treatments (ADDL+E1L, ADDH+E1H, AEDL+E1L, and AEDH+E1H). After 42 d, their basic physiological parameters, secondary sex characteristics, gonadal health, embryo numbers, and HPG axis-related gene expression were evaluated. Results showed that the P/D ratio of hemal spines in AEDH+E1H exhibited a pronounced reduction, approximately half that of E1H. Moreover, the number of embryos in ADDH+E1H and AEDH+E1H was reduced by approximately 3-fold compared to E1H. Correspondingly, G. affinis exposure to ADDH+E1H and AEDH+E1H increased the proportion of degenerated oocytes. Exposure to combined treatments led to significant changes in the transcription of HPG axis-related genes in fish and displayed a certain degree of interaction. Furthermore, cluster heatmap analysis of target genes demonstrated that ADD+E1 and AED+E1 (both high and low concentrations) were far apart from ADD, AED and E1. Collectively, these observations imply the presence of antagonistic interactions in combined treatments, and the negative impact on the growth, maturation, and endocrine system of G. affinis varies accordingly.