Dimorphism in olfactory neuroepithelium of fish, anabas testudineus (bloch, 1792): an ultrastructural interpretation

Anabas testudineus is an air-breathing teleost (IUCN Red List- ‘Least Concern’ Ver 3.1).The olfactory system of fish is a highly specialized chemosensory organ comprised of nostrils, nasal cavities, olfactory lamellae, olfactory nerves and olfactory bulbs above the brain. We conducted a study on olfactory neuroepithelium of A. testudineus to explore the surface topography and its dimorphism between different sexes (male and female). The olfactory rosettes of A. testudineus were dissected and examined under a scanning electron microscope (SEM) after fixation in 2.5% glutaraldehyde and CPD respectively. The olfactory rosette contained 8-11 numbers of lamellae and connected with an anterior raphe. The lamellae are distinguished into prominent inner sensory area bounded by outer non-sensory epithelium with different cellular components. The sensory epithelium possessed ciliated olfactory sensory neurons (CiOSNs) which remain distributed within the dense aggregations of ciliated non-sensory cells. The dispersion of non-sensory epithelium is found to vary between male and female A. testudineus. The non-sensory epithelium is branched and typically characterized by ciliated-microvillous cells that were more predominant in male A. testudineus. Hence, the olfactory neuroepithelium of A. testudineus possesses distinct sexual dimorphism. The uniqueness of ciliated sensory epithelium and ciliated-microvillous cells located in the non-sensory area reflects the specific adaptive nature of the species concerned.