Comparative Morphology of Fish Olfactory Epithelium—I*1Salmoniformes

Abstract

The olfactory rosettes of three species of salmon (Oncorhynchus nerka, O. Masou, and O. keta) were studied by scanning and transmission electron microscopy. The fine structure of the rosette is essentially similar in the three species. The sensory epithelium covers the depressed regions between the ridges of the secondary fold of the lamella. Besides the supporting cells, following four types of cells are distinguished there on the basis of the surface specialization: (1) those bearing many long cilia on the wide and flat surface (type 1 ciliated cell), (2) those bearing several short cilia which project radially from a round cell apex (type 2 ciliated cell), (3) those bearing no cilia but a tuft of numerous microvilli (microvillous cell) and (4) those bearing neither cilia nor microvilli but protruding a simple rod from the surface (rod cell). The four types show almost similar internal ultrastructure. They are surrounded by supporting cells whose free surface has many short microvilli. Sensory epithelium is mostly comprised of approximately same number of type 1 ciliated cells, type 2 ciliated cells and microvillous cells. The rod cells occur in clusters in limited areas of the epithelium. The indifferent epithelium is composed of mucous cells and epidermal cells whose surface is covered with a fingerprint-like pattern of microridges. The transitional region between the sensory and the indifferent epithelium consists of the type 1 ciliated cells and the microridge-bearing cells. © 1977, The Japanese Society of Fisheries Science. All rights reserved.