Histological and Ultrastructural Characterization of the Saccus Vasculosus in Garua Bachcha, Clupisoma garua (Hamilton, 1822)

Background: The saccus vasculosus (SV) is a highly vascular organ situated on the ventral surface of the diencephalon, adjacent to the pituitary gland. It has a restricted distribution and occurs exclusively in certain gnathostome fishes. Objective: This study investigated the cellular organization of the SV in Clupisoma garua (Siluriformes: Ailiidae) using light and electron microscopes. Materials and Methods: Sexually mature specimens of C. garua were collected from the Bhagirathi–Hooghly River, a branch of the Ganges. The SV was examined using standard histological staining, as well as scanning electron microscopy and transmission electron microscopy, to characterize its detailed structural composition. Results: C. garua possessed a moderately developed SV characterized by numerous folds that form villus-like projections. The organ enclosed a large central cavity lined by a single stratified neuroepithelium composed of specialized coronet cells (CCs) and supporting cells, with CCs being more abundant. Both cell types rested on a basement membrane in close association with vascular elements. The CCs displayed basally located nuclei and distinct apical globular protrusions. The highly branched cavity, containing abundant secretory material, communicated with the third ventricle of the brain. Conclusion: The secretory and sensory roles of the SV were correlated with the functional significance of this organ in C. garua .