Abstract
The topological characteristics of the entire gut surface of the rainbow trout were investigated utilizing the scanning electron microscope. The mucosa exhibited longitudinal ridges in the oesophagus and stomach, villi in the intestine, fine longitudinal ridges in the caeca and annular folds in the rectum, arranged as a stack of caudally‐directed funnels starting from the intestino‐rectal valve to the vent. Detailed study revealed taste pores in the anterior oesophagus and the sculpting of the luminal plasmalemma of the surface cells into micro‐ridges with complicated patterns. The surfaces of the posterior oesophagus and stomach were demarcated into polygons by rows of stubby microvilli—each polygon representing the luminal surface of an epithelial cell. Each rectal fold consisted of a smooth, caudally‐directed apex and a base which was supported by perpendicular buttress‐like secondary folds. The functional significance of these features which emphasize the vast difference in the physical length of the gut and the effective surface area is discussed.
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