Extracutaneous melanogenetic system in Dicentrarchus labrax and Sparus aurata (Linnaeus, 1758): a preliminary study.

Melanogenesis has been mainly studied in mammalian melanocytes and melanoma cells. In heterothermic vertebrates, melanin-containing cells, named melano-macrophages, occur in visceral organs (1). In Teleosts, these cells are copious and dispersed in the stroma of haemopoietic tissues in kidney and spleen. In these organs, pigment content increases in particular states such as pathological and inflammatory conditions (1). To gain a more extensive knowledge of the extracutaneous melanin-containg cell system, we investigated for the enzymes responsible of melanogenesis in two fish species: sea bass (Dicentrarchus labrax, L.) and gilthead seabream (Sparus aurata, L.). We looked for DOPA oxidase (DO) and peroxidase (POD) activity in kidney and spleen of breeding specimens caught in spring and winter. Kidney melanosomal protein fractions revealed a very high DO activity in both species. A seasonal variation of the enzymatic activity (higher in winter and lower in spring) was found. Kidney melano-macrophages also showed a POD activity with seasonal variations similar to those observed in DO activity. Assays on spleen tissue extract revealed only a POD activity in spring, whereas in winter both activities were detected. In conclusion we demonstrate, in these two fish species, that the melano-macrophages from kidney and spleen possess a melanogenetic capability that share common features with the melano-macrophages studied in other low vertebrate species. The extracutaneous melanogenetic system could be used as a biomarker for the health status of farmed fishes. Great interest is directed to human diet because of the close relationship between nutrition and health. References 1)Agius C., Roberts R. J., Journal of Fish Diseases, 200326, 499-509.