Ultrastructure Based Morphofunctional Variation of Olfactory Crypt Neuron in a Monomorphic Protogynous Hermaphrodite Mudskipper (Gobiidae: Oxudercinae) (Pseudapocryptes lanceolatus [Bloch and Schneider])

Pseudapocryptes lanceolatus (Bloch and Schneider) is a monomorphic protogynous hermaphrodite teleost that possesses ovotestis as gonadal unit of reproductive structure. At the onset of breeding season (i.e., June–July), the ovarian tissue is gradually differentiating into female-phased P. lanceolatus. At the same time, the pear-shaped crypt cells (a type of neuron) are frequently appeared at apical part of pseudostratified olfactory neuroepithelium of P. lanceolatus. The crypt neuron is characterized by the presence of sunken cilia and microvilli at the proximal region. The features of subcellular organelles are also explored in lieu of their probable functional significance. The nucleoplasm of mature crypt neuron shows chromatin granules having diameter: 15–25 nm. This cell undergoes neural apoptosis at the end of breeding phase (i.e., October–November). Fragmented chromatin fibers with numerous chromatin granules (diameter: 25–30 nm) in nucleoplasm and lysosomal diversity are the most notable characters of apoptotic crypt neuron. The large accumulation of heterochromatin chromatins in nucleoplasm is also marked under fluorescence microscope. The frequent presence of acetylcholinesterase-positive vesicles in axoplasm of crypt neurons is also a prime subcellular indicator for inhibition of neural transmission of olfactory signals. Therefore, it is concluded that the sex differentiation in P. lanceolatus and occurrence of crypt neuron in olfactory neuroepithelium are interrelated events during the reproductive period. Consequently, we hypothesized that the crypt neuron plays an active role in the implementation of unique reproductive strategy through recognition of pheromonal cues within the social organization of P. lanceolatus.