POST-HATCHING AGE CHANGES OF THE OESOPHAGUS OF TILAPIA FISH (OREOCHROMIS NILOTICUS) LIGHT AND TEM STUDIES

Document Type : Original Article

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Department of Cytology and Histology, Faculty of Veterinary Medicine Cairo University.

Abstract

The development of the oesophagus of 40 ore- ochromis niloticus fish at different post hatching ages was described using light and TEM. In newly-hatched larvae, the oesophagus appeared as a short tube lying dorsal to the yolk sac. It was initially lined by 3-5 cell layers thick. Three days post hatching, the superficial epithelial layers were expanded in several sheets toward the lumen. At the age of 8 days, the uppermost layer of the epithelium became formed of cu- boidal cells with convex free surface. The lumi- nal margin of superficial cells carried prominent microridges. Gradual flattening of these cells oc- curred till became stratified squamous at 14 days old larvae when the mucosal folds were firstly developed. At the time of hatching, the mucus cells began to develop in-between the oesophageal epithelial cells. By the 3rd day, they became filled with vacuolated cytoplasm. At 8 days, the mucus cells began to take the goblet-shape. The mucus drop- lets were more electron dense in the anterior esophagus than that of the caudal part. Primordial taste buds appeared as localized groups of undifferentiated cells at 6 days post hatching. Later on, at 8 days, their constituent cells became differentiatedintc spindle-shaped cells and basal ones. Generally, there was a tendency for taste buds to occur in the anterior part of the oesophagus toward the pharynx. They were gradually de- creased caudally till completely disappeared near the stomach whereas the mucus cells were more numerous in the posterior part of the oesophageal epithelium. From 14 days post hatching onwards, the oesophagus attained the four tissue layers arrangement characteristic of the adult 

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