Hepcidin, an antimicrobial peptide produced by the liver, also controls the iron balance and regeneration in vertebrates. Two types of hepcidin (Hamp1 and Hamp2) have been found in the bodies of black rockfish (Sebastes schlegelii). The full-length cDNA of hepcidin was cloned to enable a study of the antibacterial roles of these two hepcidins (Hamp) in black rockfish. The antimicrobial function of recombinant hepcidins was tested both in vitro and in vivo by the synthesis in Escherichia coli of recombinant hepcidin (approximately 11 kDa) from black rockfish. The recombinant hepcidins inhibited the growth of two bacterial species, Streptococcus iniae FP5228 and Pseudomonas aeruginosa, at various concentrations, in vitro after 6 h post-incubation, respectively. During infection, the production of ferroportin was reduced, suggesting the preservation of iron to prevent microbial proliferation. In vivo administration of Hamp1, but not Hamp2, synthetic peptides induced a substantial reduction in the expression of ferroportin, suggesting that in black rockfish with two forms of hepcidin, ferroportin production is regulated by the iron-regulator Hamp1, and not by the dedicated antimicrobial Hamp2. The findings of this study suggest the various antimicrobial roles of these two types of hepcidin.

Our aim was to study the relationship between the sex-determining genes, sox9a and cyp19a, and water temperature in Gadus chalcogrammus. We assessed the sex ratio based on the expression levels of sox9a and cyp19a at different water temperatures (5, 8, 11, and 14 °C) and at different stages of walleye pollock development (embryos, larvae, and juveniles). Next, we used immature walleye pollock to assess sox9a expression in males and cyp19a and vitellogenin (VTG) expression in females at different water temperatures. Males expressed sox9a in the gonadal tissues, while females expressed cyp19a in the gonadal tissues and VTG in the blood plasma. In the first experiment, cyp19a expression was higher at 5 °C and 8 °C, and sox9a expression was higher at 11 and 14 °C. In the second experiment, sox9a expression remained relatively stable, but cyp19a expression decreased with increasing temperature, decreasing significantly after 14 °C. Similar patterns were also observed for VTG expression. These results indicate that lower water temperatures increase cyp19a expression, which increases the female ratio. Higher water temperatures increase sox9a expression, which increases the male ratio. Therefore, this study highlights the potential of the sex-determining genes and the influence of water temperature.

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