GUT GLYCOCONJUGATES IN SPARUS-AURATA L. (PISCES, TELEOSTEI) - A COMPARATIVE HISTOCHEMICAL-STUDY IN LARVAL AND ADULT AGES

This study examined the gut of the euryaline fish Sparus aurata, from the pharynx to the rectum. The specimens were collected from adult ani mals, both sexes, and several larval and juvenile stages, from 4 to 13 5 days of age. Histochemical methods to distinguish neutral and acidic glycoconjugates, as well as specific techniques to identify acidic gl ycoconjugates which contained O-acylated sialic acids were used. The p resence and distribution of sugar residues in the oligosaccharide side chain of glycoconjugates were investigated with the use of biotinylat ed lectins. The pharynx and oesophagus of adult fishes showed the pres ence of abundant secretory cells which synthesized a large quantity of neutral, as well as sulphated and sialylated glycoconjugates, with di fferent cellular combinations of them in the proximal and distal tract . This may be related to the complex functions carried out by this end of the gut in a marine euryaline fish. Epithelial secretory cells wer e found in the developing oesophagus during larval life (14 days) earl ier than in the stomach and intestine (34 days). The simple columnar e pithelium that lined the gastric mucosa of adult fish synthesized a mi xture of neutral and acidic glycoconjugates, whereas during larval, li fe it was shown to contain neutral glycoconjugates only. The intestina l goblet cells were shown to secrete both neutral and acidic glycoconj ugates, especially sulphated forms. The adherent mucus gel of the gast ric and intestinal mucosa contained many sugar residues, as revealed b y lectin histochemistry. This work clearly demonstrates that the quali ty of gut mucosubstances varies in different ages and in regions of th e fish alimentary canal. This is possibly caused by changes in environ mental conditions and may in turn sustain functional alterations of th e digestive apparatus.