The pelvic fins of goby fishes are fused together to form a single pelvic sucker. The pelvic sucker allows adhesion by generating negative pressure relative to the surrounding pressure and thus aids in resisting drag from stream current flow and, in extreme case, gravity from its own body when climbing. Waterfall-climbing gobies are common in streams and estuaries of tropical and subtropical oceanic islands like Hawai’i and Dominica. They exhibit a life cycle called amphidromy, in which newly hatched larvae are swept by stream currents out to the ocean, where they develop for several months before migrating back to adult habitats in freshwater to spawn. During migration, juveniles reach upstream habitats by climbing rock surfaces of waterfalls up to 100 feet high. It is possible that differences in the climbing ability determine patterns of habitat distribution among these gobies. Movement of the pelvic sucker and the suction generated are affected by the biomechanics related to the bones of the pelvic structure, which form four-bar linkages. This image was produced as part of a biomechanical model that examines how fast and forceful these linkages move, and to see if it shows correlations with their body morphology and suction generation.