Distribution and ultrastructure of pigment cells in the skins of normal and albino adult turbot, Scophthalmus Maximus

The distribution and ultrastructure of pigment cells in skins of normal and albino adult turbots were examined with transmission electron microscopy (TEM). Three types of pigment cells of melanophore, iridophore and xanthophore have been recognized in adult turbot skins. The skin color depends mainly on the amount and distribution of melanophore and iridophore, as xanthophore is quite rare. No pigment cells can be found in the epidermis of the skins. In the pigmented ocular skin of the turbot, melanophore and iridophore are usually co-localized in the dermis. This is quite different from the distribution in larvae skin. In albino and white blind skins of adult turbots, however, only iridophore monolayer still exists, while the melanophore monolayer disappears. This cytological evidence explains why the albino adult turbot, unlike its larvae, could never resume its body color no matter what environmental and nutritional conditions were provided. Endocytosis is quite active in the cellular membrane of the iridophore. This might be related to the formation of reflective platelet and stability of the iridophore.