Scanning electron microscopic study of the structures associated with lips of an Indian hill stream fish Garra lamta (Cyprinidae, Cypriniformes).

The surface architecture of the structures associated with the lips of a hill stream fish Garra lamta was examined by scanning electron microscopy. In this teleost, the lips are inconspicuous and associated with prominent horny jaw sheaths. Furthermore, the upper and lower lips are associated with a greatly enlarged rostral cap and an adhesive pad, respectively. The rostral cap has a proximal mucogenic region and a distal keratinized region. The adhesive pad is differentiated into central mucogenic and peripheral keratinized regions. At the mucogenic regions of the rostral cap and the adhesive pad, the surface of the epithelial cells is characterised by well developed microridges, which reflect their high secretory activity. The mucus may lubricate the surface and protect the epithelia from abrasions at these regions, which are likely to be subjected to wear and tear during frequent friction and adhesion of the fish to the substrate. Taste buds may help the fish to locate food and trigger a 'pick-up' reflex. The epithelial cells at the surface of the keratinized regions of the rostral cap and the adhesive pad are modified as clusters of spine like unculi, which may assist the fish in its firm anchorage to the substrate. The epithelial cells at the surface of the horny jaw sheaths are modified as polygonal unculi, each appears much like a tooth that has a characteristic sharp edge at the margin. These may be regarded as an adaptation to browsing or scraping food materials from the substrate.