Histogenesis of the oropharyngeal and oesophageal mucosa as related to early feeding in rainbow trout, Salmo gairdneri Richardson

Abstract

The histogenesis of the oropharyngeal and oesophageal mucosa of rainbow trout, Salmo gairdneri, eleutheroembryos was studied from hatching to day 40 in relation to early feeding. Numbers of epithelial layers of the mucosa increased appreciably until day 20 but little thereafter. Differentiation of mucous cells was evident by day 10 and increased rapidly in number until about day 20. The first structurally distinct taste buds were observed in the oropharyngeal mucosa at day 8 and appeared by day 20 to be fully differentiated. An epithelial cell plug that occluded the upper alimentary canal and would have prevented passage of food into the stomach disappeared at about day 17. Teeth, although developing under the mucosa by day 3, had not yet erupted at day 22, the time of first feeding.It is suggested that the onset of first feeding in rainbow trout is in synchrony with the histogenesis of the oropharyngeal mucosa, notably the mucous cells and taste buds. The oropharyngeal mucosa of the fish that failed to feed by day 37 appeared to have undergone extensive hyperplasia while mucous cells were atypical, and taste buds seemingly deformed.