Histology and histochemistry of the development of the digestive system of larval gilthead seabream, Sparus aurata L.

Abstract

Resorption of the yolksac and development of the digestive tract and associated organs, including the swim bladder, were studied in Sparus aurata larvae from hatching until day 30 using histological and histochemical procedures. At the onset of exogenous feeding three regions could be easily distinguished in the gut: the foregut including the oesophagus and a primordial stomach, the midgut and lastly the hindgut. At this time, the digestive tract was functional even though the stomach was not yet completely developed; gastric glands, for instance, were not present in the period studied. Glycogen and zymogen grains were stored in the liver and pancreas, respectively between days 4 and 6 after hatching. Proteins were observed in the pancreas, hepatic vascular system and to a lesser extent the hepatocytes. Once feeding had commenced, the anterior intestinal epithelium developed the capacity for the absorption of lipids, most of which were included in large lipid droplets. Simultaneously, acidophilic supranuclear inclusions containing proteins were observed in the posterior intestinal epithelium. All oesophageal mucous cells, intestinal goblet cells, epithelial columnar cells in the stomach, and enterocytes of the digestive epithelium were rich in carboxylated, sulphated and/or neutral mucosubstances. Proteins were not present in digestive goblet cells.