Organization of the olfactory system of the Indian major carp Labeo rohita (Ham.): A scanning and transmission electron microscopy study

Catla catla, Labeo rohita, and Cirrhinus mrigala represent important alimentary fish in India. Their reproduction/breeding depends on seasons. Fish perceive external factors-stimuli and chemical signals through the olfactory system that plays the key role in central regulation of reproduction. However, no electron microscopy data are available on organization of olfactory components of these fish. We studied organization of the olfactory organ in male L. rohita using scanning (SEM) and transmission electron microscopy (TEM). This organ consists of olfactory epithelium, a short nerve, and olfactory bulb. The olfactory organ is ovoid in shape and consists of about 47–52 lamellae in adults and about 14–20 lamellae in fingerlings. These lamellae originate from the midline raphe. By SEM, microvillar sensory and ciliated non-sensory cells were observed in the lamellae. TEM revealed microvillar receptor cell with rough endoplasmic reticulum and Golgi apparatus towards apical end. Basal cells were present at the base of receptor cell, supporting cells were located adjacent to the olfactory receptor neurons, while epithelial cells—in the nonsensory part of olfactory epithelium. Mast, blastema, and macrophage cells were also found at the basement membrane. This work is the first publication on ultrastructural organization of the olfactory system of the Indian major carp, which provides information about morphological and ultrastructural organization of the olfactory system and opens new avenues for further investigation of chemical neuroanatomy, sensory signal processing, and neural regulation of reproduction in the Indian major carp.