Glyconjugates in epidermal, branchial and digestive mucous cells and gastric glands of gilthead sea bream, Sparus aurata, Senegal sole, Solea senegalensis and Siberian sturgeon, Acipenser baeri development

Epidermal, branchial and digestive mucous cells, and the gastric glands of larvae/postlarvae (from hatching until 45 days posthatching) of three fish species (two teleostean and a chondrostean) were investigated using convent ional histochemical methods (periodic acid schiff -PAS-, diastase-PAS; alci an blue pH 0.5, 1 and 2.5) in order to distinguish neutral and acidic (carb oxylated and sulphated) glycoconjugates, as well as bromophenol blue reacti on for identification of proteins. Additionally, the presence and distribut ion of sugar residues in the oligosaccharide side chains of glycoconjugates were investigated using horseradish peroxidase (HPR)-conjugated lectins (C on A, DBA, WGA and UEA-1). Most mucous cells (digestive, epidermal and bran chial) of Siberian sturgeon, Acipenser baeri, sea bream, Sparus aurata and Senegal sole, Solea senegalensis larvae were PAS- and alcian blue- (pH 2.5 and 0.5) positive, with small variations between organs/tissues and species . Bromophenol blue reaction (general proteins) was positive in a minority o f the mucous cells, usually in those cells which were PAS-negative. Protein s rich in sulphydryl (-SH) and/or disulphide (-S-S-) groups related with th e glycoprotein nature of the glycoconjugates present in mucous cells were a lso observed. Epidermal, branchial and digestive mucous cells of all studie d larvae did not contain glycogen or lipids. Con A lectin staining was negative in all mucous cells types of sea bream a nd sole, but oesophageal mucous cell of sturgeon were reactive to different lectin reactions, suggesting the presence of mannose -Man- and/or glucose -Glc-, L-fucose -Fuc-; N-acetyl-D-galactosamine -GalNAc-, as well as N-acet yl-D-glucosamine- GlcNAc - and/or sialic acid -NANA- residues. Digestive mu cous cells of all studied larvae were positive to WGA and DBA lectins. Epid ermal and branchial mucous cells of sea bream and sole were Con A, DBA and UEA-I unreactive. However, mucous cells of sturgeon larvae were stained wit h UEA-I lectin. Gastric glands appear very early in sturgeon stomach larvae development (be tween 5-6 days posthatching) but rather late (around 40 days) during the on togeny of sole and sea bream larvae. These glands contain neutral glycoprot eins with Man and/or Glc, Fuc, GlcNAc- and/or sialic acid and rich in GalNA c- sugar residues, as well as proteins moderately rich in arginine, and oth ers particularly rich in tyrosine and tryptophan.