Abstract
When Sicyopterus japonicus, an amphidromous goby, encounters rapids or waterfalls, it often leaves the water and climbs the rocks to bypass such obstacles.The rock-climbing of this fish is achieved by movement of the jaws and pelvic disc.When it advances on the rock its upper jaw is extended in an anteroventral direction sucking onto the rock by the inner side of the upper jaw.The pelvic disc also serves as a sucker.Then the upper jaw is constricted, thus the fish climbs even an overhanging surface by a single projection of the upper jaw.The structure of its mouth part is specialized, and the mech-anism of rock-climbing movement differs from that of other mountain-stream gobies in which the rock-climbing is performed by the sucking disc and rapid strokes of the tail.
