Progesterone affects the transcription of genes in the circadian rhythm signaling and hypothalamic-pituitary-gonadal axes and changes the sex ratio in crucian carp (Carassius auratus).

Progesterone (P4) is an extensively applied progestin in human and veterinary medicine that has been widely detected in ambient aquatic environments, which can be detrimental to the health of aquatic organisms. Here we investigate the long-term effects of P4 on the transcription of genes related to the circadian rhythm signaling pathway and hypothalamic-pituitary-gonadal (HPG) axes in the crucian carp, which may have a potentially negative on endocrine-disrupting and sex differentiation impacts. Our results suggest that the expression of genes associated with the circadian rhythm signaling pathway are altered following exposure for 10, 20, 30, 40, 50 and 60 d, leading to disorders in the endocrine system disorders and the regulation of HPG axes-related gene expression. These maladies may affect gonadal development and the reproductive systems of crucian carp and provide a plausible mechanism for the observed change in sex ratio toward females after 180 d.