International Journal of Forest, Animal and Fisheries Research (IJFAF) ISSN: 2456-8791 [Vol-6, Issue-4, Jul-Aug, 2022] Issue DOI: https://dx.doi.org/10.22161/ijfaf.6.4 Article DOI: https://dx.doi.org/10.22161/ijfaf.6.4.3 Int. J. Forest Animal Fish. Res. www.aipublications.com/ijfaf Page | 14 A Transmission Electron Microscopic Study of the Olfactory Epithelium in Hill Stream Cyprinidiae, Garra mullya (Sykes) R S Bagade, DVNS Suresh Department of Zoology, Dr Ambedkar College, Deekshabhoomi, Nagpur 440010, India Email: sureshdvns@gmail.com Received: 28 Jul 2022; Received in revised form: 11 Aug 2022; Accepted: 18 Aug 2022; Available online: 24 Aug 2022 ©2022 The Author(s). Published by AI Publications. This is an open access article under the CC BY license (https://creativecommons.org/licenses/by/4.0/) Abstract— Olfaction is primarily produced by the stimulation of receptor cells on the olfactory organ's neuroepithelial surface, surrounded by olfactory nerve fibres. Numerous fish life processes, including migration, communication, feeding, schooling, defence, and reproduction, depend heavily on olfactory signals and cues. The olfactory and reproductory systems are interconnected structurally and functionally, and puberty-related alterations in the olfactory epithelium are documented. The olfactory epithelium, which covers a large portion of the surface of the olfactory rosette, a structure found within the olfactory chambers on the fish rostrum, is where the olfactory receptor cells are situated. Although ultra structural transmission electron microscopic studies of the olfactory organ and bulb are carried out by some investigators but very sparse information is available on hillstream fishes and that is why this work has been undertaken to detail the structure of olfactory system in G. mullya by electron microscopy. Microvillous olfactory receptor cells are placed compactly adjacent to the supporting cell showing a junction complex : the zonula-ocludens. Polygonal white cells are present in between the basal cells and supporting cells. Small polyhedral basal cells lie just above the basal lamina of olfactory epithelium. Basal cells may be working as stem cells for regeneration of lost or damaged non sensory and goblet cells Keywords— olfactory epithelium, TEM, hill stream fish, Garra mullya. I. INTRODUCTION Hill streams are distinct aquatic habitats characterised by shallow, narrow channels, cold water, high altitude, various substrata, and strong water current. In order for hill stream fish to successfully adapt to this particular habitat, nature has given them a special anchorage mechanism to deal with rapid, shooting, and turbulent water flow (Ojha and Singh, 1992). The fauna is greatly influenced by current strength. Despite seasonal variations in water flow, it is always substantially higher than in plains' rivers and streams. Fish have therefore evolved sticky organs to survive the swift water flow. It is simple to categorise the fish that live in hill streams into two types. One group's members live temporarily in the highland streams and only particular times in their lives do they migrate up specifically to reproduce. These species climb simply using their muscles and do not display any unique changes. The other group has members who dwell permanently in hills' rivers and streams, and many of them have some adaptive traits. These alterations are primarily seen as sticky structures, which are typically found at the anterior end and on the fins (Arunkumar et al., 1990). These fish are all bottom-dwelling organisms by necessity. Bornean sucker, Balitora, Glyptosternum, Glyptothorax, and Pseudoecheneis are highly specialised species that have body structures that resemble leaves. Garra is a single genus, and its members exhibit every variation in body shape. Those who live in ponds and tanks have bodies that are roughly cylindrical, whereas those that live in swift- moving streams have bodies that are clearly flattened. Due to the lack of scales, the dorsal surface in front of the dorsal fin is smooth in species like Garra abhoyai and G.