SCHOENFUSS, H.L.*; BLOB, R.W.: The Effects of Larval Development on Climbing Behavior in Hawaiian Freshwater Gobies

Large waterfalls preclude most species of fish from colonizing Hawaiian freshwaters beyond the estuaries. Only three species of gobies are capable of scaling these obstacles, which they encounter during their amphidromous migration. Lentipes concolor and Awaous guamensis use rapid bursts of axial undulation to climb, whereas Sicyopterus stimpsoni slowly inches up vertical surfaces by alternately attaching oral and pelvic sucking discs to the substrate. In addition, A. guamensis and L. concolor ascend vertical surfaces primarily by climbing into or along the edge of current, whereas S. stimpsoni climb primarily on the periphery of or outside of flowing water. These differences in climbing behavior can not be attributed to differences in climbing ability, as the heights of habitats into which S. stimpsoni climb are intermediate between those of the other two species. We hypothesize that because S. stimpsoni typically loses 15% of body weight during a non-feeding metamorphosis immediately prior to climbing migrations, larvae may be in a energy-depleted condition that could preclude the use of energetically expensive rapid body movements for climbing. By slowly inching up waterfalls outside fast flowing currents, S. stimpsoni always remain attached and may be able to climb using only high endurance, red muscle fibers, thereby reducing their risk of exhaustion. Funding by Hawai�i Aquatic Resources (F-14-R-18, Fitzsimons), Office of Naval Research (N000149910184, Westneat and Walker), and by National Institutes of Health NRSA fellowships (RWB, 1F32NS10813-01 and 5F32NS10813-02).