Structural organization and histochemistry of the epithelia of the lips and associated structures of a common Indian carp, Cirrhina mrigala

Abstract

In the carp Cirrhina mrigala, the epithelia of the lips and associated structures show significant modifications in relation to the feeding behaviour of the fish and the nature of food that it consumes. The superficial layer of epithelial cells, modified to form characteristic unculi on the ventral side of the upper lip and a conspicuous epithelial cone on the apical side of the horny lower jaw sheath, is keratinized. These specialized structures help the fish to scrape the substrate, serve as a cutting edge, and assist the fish to grasp the food. The epithelia on the dorsal side of the upper lip, the rostral cap, the lower lip, and the folds of skin between the upper lip and the rostral cap and between the lower lip and skin on the ventral side of the head are unkeratinized. The mucous secretions on the surface in these regions serve primarily to protect in various ways. In addition, lubrication provided by mucous secretions in the folds of skin reduces friction during protrusion of the jaws, enabling the fish to manipulate its food swiftly and efficiently. The presence of taste buds in the epithelia in the apical regions of the lips and on the rostral cap is considered an adaptation to assist the fish in searching for suitable food.