Orange nodules in the skin of cultured turbot Scophthalmus maximus containing lipofuscin-like pigments

Orange nodules of different sizes (1 to 4 cm in diameter) were observed on the skin and fins of cultured turbot Scophthalmus maximus (L.). These nodules were located mainly in the dermis and hypodermis and were composed of numerous aggregates of pigment-laden macrophages surrounded by a mixture of epithelioid cells and spindle-shaped cells. The epithelioid cells were very large, had eosinophilic cytoplasm and contained a large nucleus formed by 1 or more lobules and prominent nucleoli. Occasional multinucleate cells were also observed. Affected turbot also displayed melanophore hyperplasia in some patches of the skin. Histochemical studies suggested that the orange pigments were lipofuscin-like substances. Affected turbot showed glomerulonephritis and dilated renal tubules. The presence of pigments in the epithelial cells of the intestinal mucosa and in the hepatocytes suggests that these substances or their precursors were included in the food and that affected turbot were unable to metabolize them.