Macro-anatomical variation of the olfactory apparatus in some Indian teleosts with special reference to their ecological habitat.

The anatomy of the peripheral olfactory apparatus (i.e. olfactory lamellae, olfactorychambers, accessory nasal sacs, olfactory nerve tracts, olfactory bulbs and brain) of some teleosts, viz. Pseudapocryptes lanceolatus (Bloch and Schneider, 1801) - an air breathing mudskipper, Lepidocephalichthys guntea (Hamilton, 1822) - a freshwater scavenger fish and Mastacembelus armatus (Lacepède, 1800) - a freshwater potamodromous fish, has been studied in relation to their specific ecological habitat. Live, adult, sex-independent fish species were collected from the local markets of West Bengal, India, and acclimatised with the laboratory conditions (for 72 h at 32°C). The specimens were anaesthetised by MS-222 (dose: 100-200 mg/L). Olfactory apparatuses were dissected out and fixed inaqueous Bouin's solution. The macro- and microstructures (using haematoxylin and eosin) of the olfactory apparatuses were examined under binocular light microscope (LM) and trinocular LM (Primo Star; Carl Zeiss Microscpy, GmbH, Germany) respectively. P. lanceolatus possesses unilamellar olfactory apparatus at therounded snout, whereas L. guntea shows small rosette with 18 to 24 lamellae oneither side of the elliptical snout. Elongated olfactory rosette (number of lamellae ranges from 60 to 76) is present at the pointed snout of M. armatus. Morpho-anatomical variation in snout structure of the respective species is an indicative of divergence in ecological habitat, but variation in olfactory apparatus is significant for species-specific differentiation. Pseudostratified olfactory neuroepithelial components (i.e. sensory receptor cell, supporting cell and basal cell) show striking similarities amongst these species. Therefore comparative anatomical changes of the snout and olfactory apparatus are not only representing ecological habitat based on interspecific variation, but may also indicate the phylogenetic relation amongst said species.