PNA ‐lectin histochemistry shows putative epidermal cells secreting antifreeze glycoproteins ( AFGPs ) in the Antarctic fish Trematomus bernacchii (Boulenger, 1902)

The epidermis of fish species which inhabit the frigid waters of the Antarctic realm can be expected to form a protective thermal barrier around them, involving their epidermis. The present study, mainly using lectin-histochemistry, identifies in the epidermis of the Antarctic fish Trematomus bernacchii the presence of numerous cells that secrete likely antifreeze glycoproteins (AFGPs) for thermic protection from extremely cold water. The PNA-FITC conjugated lectin recognizes the known galactosyl-N-acetylgalactosamine disaccharide that forms the long repetitive glycidic units of the AFGPs. The mucus-secreting cells represent 3.1% average of total epidermal cells, are evenly distributed in the epidermis and their secretion is mainly discharged on the epidermal surface, contributing to the formation of the secreted mucus cuticle. Furthermore, the AFGPs are positive for glycoprotein/glycolipid production in the epidermis, as indicated by general histochemical and ultrastructural methods, namely Blue Nile Sulphate and silver-methenamine reactions. Lipid material likely derives from the differentiating keratinocytes during their movement toward the epidermal surface where they are eventually desquamated. Some AFGPs are present with a diffuse distribution also in the dermis. The study indicates that not only AFGPs but also some lipids likely effectively protect the epidermis that is the first tissue in contact with the cold marine waters of Antarctica.