Meeting Abstract

3.1  Friday, Jan. 4  Backwards swimming by bluegill sunfish requires multifin coordination FLAMMANG, B.E.**; LAUDER, G.V.; Harvard University bflammang@post.harvard.edu

Teleost fish, like the bluegill sunfish, have multiple flexible fins that are used as modifiable control surfaces. This helps to make fish highly maneuverable, permitting behaviors like reversing direction of motion and swimming backwards without having to rotate body position. To answer the question of how fish swim backwards we used high–speed videography and electromyography to determine the kinematics and muscle activity necessary to produce reverse direction propulsion in four bluegill sunfish. Comparison of backwards swimming to forwards swimming determined that the two swimming modes are not reciprocal actions. To swim forwards at low speeds, sunfish primarily used their pectoral fins only without appearing to use any other fins. Conversely, backwards swimming is a multifin effort, utilizing the pectoral, dorsal, anal, and caudal fins. The pectorals alternate direction synchronously, broadly flared on the outstroke and feathered on the instroke. The dorsal fin and dorsal portion of the caudal fin act out of phase as do the anal fin and ventral portion of the caudal fin. Electromyography of all muscles in the pectoral, dorsal, anal, and caudal fins demonstrated bilateral activation when the fin changed direction, suggesting that the fin is stiffened at this point. Because teleost fish are statically unstable, locomotion at slow speeds requires precise fin control to adequately balance the torques that are produced about the center of mass. Therefore, we expect that bluegill sunfish require a coordinated multifin motion pattern in order to swim backwards in a controlled manner.