Abstract Transferrin (Tfa) plays an important role in iron regulation and is also known to be involved in response to infections. In this study, the full-length cDNA of the transferrin gene from Lutjanus argentiventris was cloned and characterized. The full-length cDNA of the tfa was 2482 bp encoding 690 amino acids containing an N-terminal signal peptide and the two conserved lobes. Tfa protein was highly similar to fish transferrins such as those from Larimichthys crocea (80%), Pagrus major (80%) and Dicentrarchus labrax (80%). Transferrin constitutive expression was found to be the highest in spleen and head-kidney. Moreover, the mRNA expression levels of tfa were measured by real-time PCR at 24 and 96 h in juveniles exposed to iron (Fe2x) during Aeromonas hydrophila infection. In general, the expression of tfa decreased in liver and intestine and increased in gill and skin in the iron group compared to control. The iron followed by Aeromonas hydrophila infection group caused a down-regulation in transferrin gene expression in all analyzed tissues at any point during the experiment. These findings demonstrate the evolutionary conservation of transferrin functions in vertebrates, involved in both the immune response and iron metabolism.