Organogenesis of the digestive tract in the white seabream, Diplodus sargus. Histological and histochemical approaches

Abstract

The ontogeny of the digestive tract of the white seabream, Diplodus sargus during the larval development up to day 45 post-hatching (dph) has been studied using histological and histochemical techniques. The oesophageal goblet cells appeared around 6 dph and contained neutral and acid mucosubstances (PAS/diastase-PAS and Alcian Blue pH 2.5 positive reactions). An incipient stomach can be distinguished from 2 dph but the first sign of gastric gland development was detected around 13-15 dph, increasing in number and size by 22-23 dph. Gastric glands were concentrated in the cardiac stomach region and they had a high content of protein rich in tyrosine, arginine and tryptophan. Acidophilic supranuclear inclusions related to pynocitosis of proteins, were already observed in the intestinal cells of the posterior intestine around 4-6 dph (exogenous feeding) and they were present until 25 dph. The intestinal mucous cells appeared between 15-18 dph and contained a mixture of neutral and acid mucosubstances/glycoconjugates, carboxylated ones being more abundant than the sulphated ones. The stomach and gastric glands were fully developed by the first month of life marking the beginning of digestive features characteristic of the juvenile stage. Around 4-6 dph, glycogen, proteins and neutral lipids were observed in the granular cytoplasm of hepatocytes. Strongly acidophilic zymogen granules were also present, at this time, in the basophilic cytoplasm of the exocrine pancreatic acinar cells and contained abundant proteins, especially rich in arginine, tyrosine and tryptophan.