A detailed description of the gas bladder, the Weberian apparatus and the membranous labyrinth in Sisor rabdophorus is given. It has been shown that these structures show a number of specializations which can be correlated with the bottom-living habits of the fish. Evidence has been brought forth to show that the Weberian mechanism continues to serve as an aid to hearing.
It has been concluded that Günther's inclusion of Sisor in the group Hypostomatina along with certain loricariid and callichthyid genera is not a natural one and that Regan's (1911) and Berg's (1940) family Sisoridae is more indicative of natural relationships. That Sisor diverged early from the main stem of sisorid evolution, is further supported by this study.