Histochemistry of complex glycoproteins in the digestive tract mucosa of Atlantic bluefin tuna (Thunnus thynnus L.)

The histological structure, as well as content and distribution of glycoproteins (GPs) in the digestive tract mucosa, of the Atlantic bluefin tuna were studied. The digestive tract is short in accordance with their predatory nature and consists of the oesophagus, stomach and intestine. The short oesophagus has deep longitudinal folds and contains an abundance of secretory cells which synthesize a large quantity of neutral as well as sulphated and silylated GPs. The stomach is an elongated sac-like structure with simple tubular glands surrounded by connective tissue. The neck cells of gastric glands synthesize a mixture of neutral and acidic GPs. The intestine is short with many intestinal villi. Many goblet cells are situated between superficial epithelial cells. The intestinal goblet cells were shown to secrete both neutral and acidic GPs.