Infectious diseases and breeding conditions can influence fish health status. Furthermore it is well known that human and animal health are strongly correlated. In lower vertebrates melano-macrophage centres, clusters of pigment-containing cells forming the extracutaneous pigment system, are widespread in the stroma of the haemopoietic tissue, mainly in kidney and spleen. In fishes, melano-macrophage centres play an important role in the immune response against antigenic stimulants and pathogens. Hence, they are employed as biomarker of fish health status. We have investigated this cell system in the European sea bass (Dicentrarchus labrax L.) following the enzyme activities involved in melanin biosynthesis. We have found a possible relationship between kidney disease of farmed fishes and dopa oxidase activity level, suggesting it as an indicator of kidney disease. Moreover variations of dopa oxidase activity in extracutaneous pigment system have been observed with respect to environmental temperature. At last, for the first time, using femtosecond transient absorption spectroscopy (Femto-TA), we pointed out that pigment-containing cells of fish kidney tissue present melanin pigments.Graphical abstract
It was found a relationship between kidney disease of farmed European sea bass (Dicentrarchus labrax L.) and dopa oxidase activity level, demonstrating the DO activity as a possible indicator for fish kidney nephrocalcinosis whose diagnosis can be, simply, highlighted by a gross examination of the farmed fishes during the autopsy. Moreover variations of dopa oxidase activity in extracutaneous pigment system have been observed with respect to environmental temperature. The comparative Femto-TA analysis of pigments isolated from sea bass kidney tissue, fish skin melanin, natural melanin from Sepia officinalis and synthetic melanin, by pointing out that fish melano-macrophages centres do contain melanins.