Light and electron microscopic studies on the oesophageal epithelium of the rainbow trout, Salmo gairdneri.

The oesophageal epithelium of the rainbow trout, Salmo gairdneri, showed a gradual transition from stratified cuboidal type containing mainly filament-containing cells and globular Type I mucous cells anteriorly to a simple columnar type composed entirely of Type II mucous cells distally. Taste buds were present in the anterior portion; mucous glands were located in the lamina propria in the middle portion and these were replaced with gastric-type glands in the terminal portion. Type I mucous cells severally produced neutral, carboxylated and sulphated mucosubstances while each Type II cell produced all the three types of mucosubstance. In the higher layers of the anterior multilaminar epithelium, the cytoplasm of the filament-containing cells contained numerous small vesicles with cores of flocculent material and the luminal aspects of the surface cells bore microridges. The vesicles contained in Types I and II mucous cells differed in size, arrangement and mode of release. These findings suggest that there is maximal development of protective features, both structural and lubricatory , which aid the oesophagus in the conduction of food materials. Additional sensory and digestive functions are also indicated.