SCHRANK, G. D.; BLOB, R. W.*; SCHOENFUSS, H. L.; St. Cloud State University, Minnesota; Clemson University, South Carolina; St. Cloud State University, Minnesota: Ontogenetic changes in red and white muscle fiber distribution in two species of waterfall climbing Hawaiian fishes
Two species of Hawaiian amphidromous gobies are remarkable in their ability to climb tall waterfalls. Larvae of Lentipes concolor climb by rapid bursts of axial undulation (25 ms duration) with long rest periods during which the animal is attached to the waterfall with its pelvic sucking disk. Larvae of Sicyopterus stimpsoni alternately attach pelvic sucking disk and sucking mouth to the waterfall and climb in prolonged bouts with short rest periods. Based on the differing larval climbing styles and physiological constraints in adult high speed undulations, we hypothesized that propulsive musculature in larval L. concolor would be dominated by fast, white muscle fibers while the musculature in S. stimpsoni would include more slow, red muscle fibers. We also predicted a shift from white to red fibers with growth in L. concolor. Specimens for this study were collected in Hakalau Stream, Island of Hawai�i, sectioned, and frozen at �80� C in isopentane. Serial sections (12 µm) were made at �20� C and ATPase activity in transverse sections of muscle were evaluated by histochemical staining. As predicted, larval L. concolor tail musculature was dominated by white muscle fibers while in larval S. stimpsoni red muscle fibers dominated propulsive musculature. Adults of both species exhibited peripheral bands of red musculature and a core of white fibers in the tail section. Red muscle bundles were prominent along the midlateral line. Adult pectoral fin musculature in both species was complex in red/white muscle fiber distribution. These results suggest that differences in muscle fiber type distribution may contribute to differences in locomotor performance between these species.
