Adaptive Modifications in Four Fish Species of the Genus Garra (Teleostei; Cyprinidae) in Basistha River, Assam, India.

This paper deals with the study of the surface morphology of barbels, upper lips, and adhesive discs in four hill stream fish species collected from Basistha River, a torrential river in Guwahati city, Assam, India. The four species belonging to the genus Garra namely, Garra gotyla (Gray, 1830), Garra gravelyi (Annandale, 1919), Garra stenorhynchus (Jerdon, 1849), and Garra nasuta (McClelland, 1838) were collected from the same torrential habitat. These fish revealed anatomical peculiarities in their barbels, lips, and adhesive discs which are believed to help them in adapting to such habitats. Organs exhibiting adaptive modifications (barbels, lips, and adhesive discs) were studied with the scanning electron microscope. The study primarily revealed the presence of type I and type II taste buds in the barbels, lips, and adhesive discs, and numerous unculi surrounded by microridges in the upper lips and adhesive discs. A cumulative, intercalated action of these organs enables these fish to adhere and adapt to rocky, torrential streams. Special ability to adapt to these habitats was reflected from the two types of taste buds (I and II) present in the barbels, and the clustering of excrescencies bearing unculi in the lips and adhesive discs of the fish.