Meeting Abstract
Hillstream loaches (Balitoridae) inhabit the fast flowing hillstreams of South and Southeast Asia. These fishes have evolved behavioral and morphological characteristics necessary to survive in these torrential streams, including the evolution of a robust pelvic girdle modified sacral ribs. The modified ribs create a skeletal connection between the vertebral column and the puboischiadic plate. Previous researchers have suggested that this connection likely evolved as a means of facilitating station holding in their rheophilic environment. We expect the tetrapod-like walking behaviors observed in balitorids to be facilitated by this skeletal connection. Within the family there is variation in the amount of modification of the sacral rib which can be divided into three morphotypes: 1, elongated sacral ribs with similar thickness to anteriorly adjacent ribs; 2, enlarged and elongated sacral ribs; and 3, enlarged and elongated sacral ribs with a flared crest. All three morphotypes have the sacral rib inserting at the lateral foramen of the pelvic plate and secured via a ligamentous support. We hypothesize that increased pectoral girdle stability will result in greater terrestrial walking performance. Performance is measured by comparative kinematic variables including timing of fin placement; walking velocity; and fin, head, and tail angle. Here we compare the walking kinematics of two species of hillstream loaches, Homaloptera parclitella and Cryptotora thamicola, which exhibit morphotypes 1 and 3 respectively.
