In the present study, the adhesive organ (AO) of Hara hara, a hillstream catfish, has been investigated using scanning electron microscopy, histology, and glycoprotein, protein, and lectin histochemistry. The AO is a disc-like structure present on the ventral side of the body. It is distinguished into a major flat central region and a narrow flap-like region at the periphery of the central region. The free surface of the AO is characteristically differentiated into plaques separated by furrows. Surface epithelial cells in the plaques are modified into unicellular spine-like unculi. The furrow epithelium contains three types of unicellular gland cells (the mucous goblet cells, the club cells, and the sacciform cells), along with sensory structures such as the taste buds (TBs). Gland cells are involved in the elaboration of various glycoproteins (oxidizable vicinal diols, carboxyl groups, and O-sulphate esters); protein moieties (basic proteins, cysteine-bound sulphydryl groups, keratin, tyrosine, protein bound-NH2 groups, and elastin); and glycans (galactose, N-Acetylgalactosamine, and fucose). Presence of these glycoprotein and protein moieties elaborated by the cellular component of the AO has been associated to play an important role in maintaining structural integrity of the epithelium, keratinization, protection against pathogens, and adhesion of the fish to the substratum. The TBs located at the summit of the tubercles in the furrow epithelium may serve as an adaptation to enhance sensitivity to food selection and environmental perception. Overall, this study provides a comprehensive understanding of the structural and functional adaptations that enable H. hara to maintain effective attachment and thrive in turbulent hillstream environments.
Sharma et al. (Thu,) studied this question.