Seasonal variations of Rana esculenta L. skin tyrosinase

Administration of a polyphenol-enriched feed to farmed sea bass (Dicentrarchus labrax L.): Kidney melanomacrophages response

The reinforcement of the defense mechanism of fish, through the administration of immunostimulants, is considered as a promising alternative to vaccines. Natural immunostimulants such as polyphenols, flavanoids, pigments and essential oils can modulate the innate immune response. In lower vertebrates, melano-macrophage centres, i.e. clusters of pigment-containing cells forming the extracutaneous pigment system, are wide-spread 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. In the present study, we evaluated the effect of a polyphenol-enriched diet on the health status of European sea bass (Dicentrarchus labrax L.). Farmed sea bass were administered a feed containing a phytocomplex, rich in catechins and epigallocatechins, which was obtained from the seeds of Canosina Nero di Troia Vitis vinifera and mixed with conventional feed at two different concentrations. The effects of such a diet were investigated in juvenile and commercial size samples, i.e. undergoing a short- and long-term period of diet, respectively, focusing on their extracutaneous pigmentary system and, in more detail, on the enzymatic activities leading to melanin biosynthesis. Our results show that prolonged dietary treatments with higher concentration of polyphenols might modulate tyrosinase activity and gene expression in commercial size fishes. An increase of melano-macrophage activity is correlated to a stimulation of cytoprotective functions against antigenic stimulants and pathogens, as an expression of a robust and protective adaptive immune response.

A multidisciplinary study of the extracutaneous pigment system of European sea bass (Dicentrarchus labrax L.). A possible relationship between kidney disease and dopa oxidase activity level

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.

Melanogenesis in visceral tissues ofSalmo salar. A link between immunity and pigment production?

Melanogenesis is mostly studied in melanocytes and melanoma cells, but much less is known about other pigment cell systems. Liver, spleen, kidney, and other organs of lower vertebrates harbour a visceral pigment cell system with an embryonic origin that differs from that of melanocytes. In teleosts, melanin-containing cells occur in the reticulo-endothelial system and are mainly in the kidney and spleen. The Atlantic salmon ( Salmo salar L.) is an ichthyic breeding species of considerable economic importance. The accumulation of pigments in salmon visceral organs and musculature adversely affects the quality of fish products and is a problem for the aquaculture industry. With the aim to reveal novel functions and behaviour of the salmonid extracutaneous pigment system, we investigated aspects of the melanogenic systems in the tissues of Atlantic salmon, as well as in SHK-1 cells, which is a long-term cell line derived from macrophages of the Atlantic salmon head-kidney. We demonstrate that a melanogenic system is present in SHK-1 cells, head-kidney, and spleen tissues. As teleosts lack lymph nodes and Peyer’s patches, the head-kidney and spleen are regarded as the most important secondary lymphoid organs. The detection of tyrosinase activity in lymphoid organs indicates that a link exists between the extracutaneous pigmentary system and the immune system in salmon.