Meeting Abstract
Kryptolebias marmoratus (Cyprinodontiformes), the mangrove rivulus, is a quasi-amphibious species of fish known to make directed movements on land by means of a tail-flip behavior involving the axial musculoskeletal system. We asked whether the morphology and fiber type of the axial myotomes have been specialized to facilitate this terrestrial behavior. We compared two different populations of K. marmoratus, one from Lighthouse Reef Atoll, Belize, and one from the Florida Keys, Florida, USA, to size-matched non-amphibious juvenile Micropterus salmoides (Perciformes), the largemouth bass, via gross dissection and muscle fiber typing using antibody staining. For gross dissection, preserved specimens of K. marmoratus (n = 4) and M. salmoides (n = 3) were skinned and stained with Lugol’s iodine prior to being photographed by a light microscope. Detailed drawings of muscle morphology were made with a camera lucida along with taking and importing photographs into Canvas. We found that the myotomal arrangement of the mangrove rivulus has a “V” shape with respect to the long axis of the body, with distinct dorsal and ventral longitudinal bundles of muscle, differing from the characteristic “W” morphology of teleost myomeres as exemplified by the juvenile bass. For muscle fiber typing, specimens (n = 8 K. marmoratus [n = 4 per population]; n = 3 M. salmoides) were fixed in Carnoy’s solution and stained with primary antibodies S58 and MF20 for immunohistochemistry. Both populations of K. marmoratus were found to have only fast glycolytic muscle fibers in both anterior and posterior axial regions, with no slow oxidative fibers present. We suggest that the morphological and fiber type differences in K. marmoratus represent specializations for terrestrial jumping.
