COMPARATIVE MORPHOLOGICAL AND HISTOLOGICAL STUDIES ON THE OLFACTORY ORGAN IN TWO MODELS OF BONY FISHES (MUGIL CEPHALUS AND MALAPTERURUS ELECTRICUS): LIGHT AND ELECTRON MICROSCOPIC STUDIES

Abstract

The olfactory organs of Mugil cephalus and Malapterurus electricus were investigated by light and electron microscopy. The olfactory rosettes of the Mugilcephalus are elongated as compared to the oval rosettes of Malapterurus electricus. Each olfactory rosette is situated in a closed olfactory chamber between the anterior tubular inlet nares and the posterior outlet openings. Each olfactory lamella is lined by typical neuron-sensory olfactory epithelium. Bipolar olfactory receptor neurons, supporting cells and basal cells are the prominent cellular components of this epithelium. Three types of receptor cells were distinguished as ciliated, microvillous and rod cells. Another type of sensory cells called crypt cells were only observed in Mugil cephalus.  Ciliated non sensory cells were also observed in the two studied species, but they are abundant in Malapterurus electricusand they have often been described as a respiratory type. They are structurally similar to the respiratory epithelial cells in the nasal cavities of tetrapods, indicating their role in mediating fluid flow over the olfactory epithelium. The non-sensory cilia have the general 9+2 pattern. The sensory and non-sensory epithelia are covered by a mucous layer, which was provided with the secretion of goblet cells that were situated mostly in the peripheral regions of each lamella. The non-sensory epithelium is composed of goblet cells and epidermal cells whose surface is covered with a fingerprint- like pattern of microridges.