The Biobrio 13(1 & 2), 2026

The olfactory organ of Macrognathus aculeatus: morphology, functional significance and growth-related variation

Ashish Kumar

ABSTRACT:

The present study investigates the morphology, histological organization, and functional significance of the olfactory organ in Macrognathus aculeatus, a benthic freshwater teleost inhabiting turbid aquatic ecosystems of the Ganga basin region. Specimens of different size groups collected from freshwater habitats of Gaya and the Phalgu River basin were examined through gross morphology, whole-mount preparations, histological analysis, and morphometric observations. The olfactory organ was found to be highly specialized, consisting of an elongated olfactory rosette with numerous claw-shaped lamellae arranged perpendicularly on either side of a median raphe. Histological studies revealed a well-developed olfactory epithelium containing receptor and supporting cells, while observations on water flow demonstrated an efficient circulation mechanism through the tubular anterior and oval posterior nostrils. Morphometric analysis indicated a progressive increase in lamellar number with increasing body size. Statistical evaluation showed a strong positive correlation between standard length and total number of olfactory lamellae, r = 0.888. The results suggest that olfactory sensitivity increases during ontogenetic development and that the species relies predominantly on chemoreception for feeding, orientation, and environmental perception. The study establishes M. aculeatus as an olfaction-oriented fish possessing marked structural adaptations to benthic and low-visibility freshwater habitats. These findings contribute significantly to the understanding of sensory biology and ecological adaptation in freshwater teleosts.

Keywords:    

Olfactory organ, Macrognathus aculeatus, lamellae, rosette, teleost fish

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