Histochemistry of the development of the digestive system of Siberian sturgeon during early ontogeny
Abstract
At hatching, the yolk-sac matrix of Siberian sturgeon Acipenser baeri contained neutral glycoconjugates, glycogen, proteins rich in arginine, lysine, tyrosine, cysteine and cystine, glycoproteins containing mannose (Man) and/or glucose (GLC), N-acetyl-D-galactosamine (GalNAc) residues, as well as neutral and acidic lipids. Buccopharyngeal and anterior oesophageal goblet cells produced a combination of neutral and acid sialoglycoproteins, while those from the posterior oesophagus secretd only neutral glycoproteins ; both types of secretions contained tryptophan and -S-S- groups and were unreactive to lectin techniques. Most intestinal goblet cells secreted mainly carboxylated and sulphated sialoglycoproteins with some rests of neutral glycoconjugates, while few of them produced only aid or neutral glycoproteins. Intestinal glycoproteins were rich in GalNAc and sialic acid residues. Close relationships between digestive enzymes and morphological development of digestive organs were observed. Histochemistry of enzymes revealed that just after hatching, alkaline and acid phosphatase, ATP-ase and non-specific esterase activities were detected in the yolk sac. From the onset of exogenous feeding to the juvenile stage (30 days post-hatch), an enhancement of enymatic activities was observed, as alkaline and acid phosphatase, ATP-ase, aminopeptidase M and nonspecific esterase sharply increased. However, lipase activity decreased int he liver and brush border of enterocytes by 13-14 days post-hatch. Two types of lipase were detected in the alimentary canal, a non-pancreatic lipase that was secreted in the cardiac stomach by gastric glands, and a pancreatic lipase, which activity was mainly detected in the brush border of the intestinal epithelium.