Effects of vitamin D3 on embryonic development, transcripts of genes encoding reproductive hormones, and its active metabolism in common carp (Cyprinus carpio L.).

Vitamin D3 (VD3) is a pleiotropic hormone with diverse physiological functions, but its role during early embryonic development in fish remains poorly understood. This study investigated the effects of aqueous VD3 exposure on embryonic survival, hatching, and the expression of the kiss1, kiss2, gnrh3, foxr1, and hsp70 genes in common carp (Cyprinus carpio L.). We also examined the hypothesis that common carp embryo is a site of VD3 non-genomic action and its metabolism, evaluated by measuring 25-hydroxyvitamin D3 (25OHD3) levels and confirmed by immunolocalization of VDR, PDIA3 as well as CYP24A1 and CYP27B1. The eggs (obtained from 6 females) were fertilized and incubated in water containing VD3 at concentrations: 0, 1, 10, 50, and 100 ng/mL. During early embryonic development (24, 48, 72 h post-fertilization - hpf), VD3 did not reveal developmental abnormalities and mortality in common carp but increased larvae hatching rate at the highest tested concentration. Furthermore, early life exposure to VD3 has shown no alteration in kiss1, kiss2, gnrh3, foxr1, hsp70 gene expression in newly hatched larvae. Crucially, VD3 exposure altered embryonic 25OHD3 concentrations. This finding, alongside the immunohistochemical localization of VDR, PDIA3, CYP27B1 and CYP24A1 in the tissue of common carp embryo, indicates the possible genomic and non-genomic action of VD3 as well as its active metabolism (synthesis and inactivation) at early life stages of this species. These findings encourage further studies to better understand the role of VD3 in reproduction and early life stages in cyprinids.