Histological Studies on Yolk Utilization and Digestive Function in Laｒvae and Juvenile of Red Sea Bream and Black Sea Bream

Histological and Histochemical studies were carried out on the yolk utilization and digestive function of larval and juvenile red sea bream,Pagrus major,(from 0 to 40 or 46 days old) and black sea bream, Acanthopagrus schlegeli,(from 0 to 40 days old) reared with rotifers, Artemia nauplii and commercial diets in hatcheries. Yolk―sac larvae of red sea bream and black sea bream absorbed glycogen from the yolk through the vitelline membrane by the age of 3 days and treated the lipoprotein of yolk altered to hyaline droplets and the oil globule througth the action of vitelline membranous cells by the age of 7 days. Postlarval red sea bream started feeding at 5 days old,and fat absorption by epithelia in the mid- and posterior intestinal regions and ingestion of water-soluble materials and albuminous granules by rectal cells were apparent in 6 or 7-day-old individuals.The ingestion of protein by rectal cells became more active with age. Fine albuminous granules were ingested in the apical edges and albuminous droplets were contained,digested within supranuclear vacuoles by 34 or 35 days old. Postlarvae at 28 days showed gastric gland differentiation and 35-day juvenile had formed pyloric ceca. Subsequently 46 days old. Fat absorption in mid‐and posterior intestinal epithelia lasted until 33 days old. The Fat absorption in posterior intestinal epithelium was marked in individuals from 26 to 33 days old that had been fed on Artemia nauplli. Rectal cells also carried out fat (lipoprotein) absorption from 11 to 28 days old. On the other hand, larval black sea bream started feeding at 5 days old and ingested water-soluble materials and protein into rectal cells. Active protein ingestion by rectal cells was observed in the form of fine granules at the apical edges and droplets in the supranuclear vacuoles from 9 to 17 daysold. Then,fine granules at the apical edges and colloidal materials in the supranuclear vacuoles appeared from 18 to 33 days old,and fine granules were evident at the apical edges by 37 days old. 29-day juvenile had formed gastric glands and pyloric ceca. Fat absorption was carried out by rectal cells in individuals from 9 to 17 days old and in the epithelium of the posterior intestinal region in individuals from 24 to 33 days old that had been fed on Artemia nauplii