The marine medaka Oryzias melastigma – A potential marine fish model for innate immune study

► Two hepcidin genes (OM-hep1 and OM-hep2) were identified in Oryzias melastigma. ► The expression level of both OM-hepcidins increased with embryo development. ► Both OM-hepcidin transcripts greatly demonstrated in liver of O. melastigma. ► Both OM-hepcidins were significantly expressed in tissues with bacterial challenge. The objective of this study is to develop the marine medaka Oryzias melastigma as a potential marine fish model for innate immune and immunotoxicological studies. Hepcidin plays an important role in innate immune system. Two hepcidin genes (OM-hep1 and OM-hep2) were identified and characterized in the O. melastigma, which were highly conserved with other reported hepcidins. During embryogenesis, significant elevation of OM-hep1 and OM-hep2 transcripts were coincided with liver development in the embryos. In adult medaka, differential tissue expressions of both hepcidin transcripts were evident: high in liver, moderate in spleen and low in non-immune tissues. After bacterial challenge, the two hepcidin mRNAs were rapidly and remarkably induced in liver and spleen, suggesting the two OM-hepcidins in O. melastigma play a complementary role in innate defense. Gender difference in time of induction and extent of the two hepcidin mRNAs elevation in infected O. melastigma should be considered in immunotoxicological studies.