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Cytoarchitectonic pattern of the telencephalon of a dwarf snakehead, Channa gachua, is studied by serial transverse sections of the brain (Kluver and Barrera staining). On the anteriormost extremity of the telencephalon, olfactory bulbs terminate that are sessile. The olfactory bulbs comprise four concentric layers, which from outside toward the center are olfactory nerve layer, a glomerular layer, mitral cell layer, and internal cell layer. Large terminal nerve ganglion cells are prominently visible in the dorsomedial position where the bulbs terminate on the telencephalon. In all, 24 nuclei are identified in the telencephalon on ventral and dorsal areas and are named according to their position. Ventral telencephalon exhibits 11 nuclei. On the dorsal telencephalon, there are 13 nuclei. These again are named according to their position on dorsal, ventral, median, lateral, or posterior part. This study reported for the first time in this fish will be useful in tracing the neuronal system of Channa gachua and subsequent studies of the functional aspects of these nuclei in the regulation of reproductive cycle of this species.

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BackgroundAs in other vertebrates, olfactory sensory neurons (OSNs) in fishes are the main components of sensory part of olfactory epithelium that relay olfactory information (smell and taste) to the brain.PurposeObjective of the present study was to analyze if any polymorphism occurs in the OSNs in a featherback fish, Notopterus notopterus as far as the teleost lineage is concerned.MethodsWith the help of neuronal staining technique, polymorphism of OSNs in N. notopterus was studied.ResultsThree polymorphic forms of OSNs were identified which are ciliated OSNs, microvillus OSNs and crypt OSNs. These morphotypes were identified on the basis of location of their somata within the depth of olfactory epithelium and resulting length of their dendrites. The ciliated OSNs have basally situated somata and long, thin dendrites with a few apically arranged cilia while microvillous OSNs have somata located midway in the epithelium and thick moderate-length dendrites with microvilli. Third cell type is crypt OSNs which are spherical or pear-shaped, located apically just close to the epithelial surface having cilia and microvilli in an invagination and devoid of any dendrite.ConclusionN. notopterus belongs to order Osteoglossiformes which is a representative of an early evolutionary lineage of teleost fishes. OSN polymorphism reported in the present work indicates that it is a fairly conserved trait throughout the evolution of teleosts. To our knowledge, we are the first ones to report OSN polymorphism in a member of the order Osteoglossiformes.