The results of a detailed study on the adhesive apparatus of Indian hill stream cyprinid and sisorid fishes are presented. The structure of the mental suctorial disc in the genus Garra is described. Histological study of the mental region of Crossocheilus and Psilorhynchus has also been made and compared with the mental disc of Garra. The muscles of the disc which control its movements in bringing a partial vacuum during adhesion have been investigated. The complexity of the geniohyoideus muscles in Garra is interesting. Variations in the degree of development and histological modifications of the mental disc are exhibited by the fishes of the genus Garra.
A thoracic adhesive apparatus in the form of longitudinal or transverse ridges and grooves is present in the sisorids, Laguvia, Glyptothorax and Pseudecheneis except Gagata. A close study has revealed that the adhesive apparatus of the catfishes works mainly on the principle of friction. The variations in shape, size and location of the adhesive apparatus in various species are correlated to their respective habitats.
Structural variation in the adhesive apparatus of Pseudecheneis is maximum in comparison to that in Laguvia and Glyptothorax. It is discovered that the modifications are associated with the presence of multi‐spinous layers, formation of caps by the basal or holdfast cells and with the transformation of loose areolar tissue into thick collagenous dermis. The presence of a pad of adipose tissue in the region of the adhesive apparatus has been reported and its physiological significance as a source of stored food suggested.
The anterior part of the protractor ischii muscle is modified to control the action of the adhesive apparatus. In Pseudecheneis, besides the m. protractor ischii, the ventral part of m. mesioventral is also associated with the adhesive apparatus.
This paper deals with the functional morphology of the pelvic girdle and fins in various genera of hill stream cyprinid and sisorid fishes. The pelvic plate of Pseudecheneis shows the greatest modification; it is unusually large and reaches the coracoids of the pectoral arch in front.
The elaborate working of the pelvic muscles and their function in bringing about effective adhesion by the pelvic fins is described in detail. The formation of a new muscle, M. pars retractor ischii of the M. mesioventralis, is reported in Garra and Psilorhynchus (Cyprinidae) and in Glyptothorax and Pseudecheneis (Sisoridae). In Pseudecheneis, the complete separation of this muscle from the M. mesioventral, and modification of the M. protractor ischii, are discussed in relation to the crawling habit of the genus. The appearance of the M. arrector pel vicalis ventralis in Glyptothorax and Pseudecheneis among sisorids has been associated with the adhesive function of the outer ray.
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