69.8 Jan. 7 Speed-dependent intrinsic caudal fin muscle recruitment during steady swimming in bluegill sunfish FLAMMANG, B.E.**; LAUDER, G.V.; Harvard University; Harvard University email@example.com
There are 56 muscles that control modulation of the tail fin in teleost fishes. Although much research has been conducted on the fluid dynamic properties of the caudal fin in fishes, little work has been done on the intrinsic musculature that controls and shapes the fin. Five bluegill sunfish (Lepomis macrochirus) were anaesthetized and electrode wires were surgically placed into intrinsic caudal muscles, up to 13 at a time. A total of 24 intrinsic muscles were studied, and activity was correlated with synchronous recordings from myotomal fibers in the caudal peduncle. After recovery, fish swam at steady speeds of 0.5, 1.2, and 2.0 L s-1, while filmed from lateral, posterior, and ventral views simultaneously at 250 frames s-1. Video sequences of tail beats were digitized in 3-dimensions to quantify fin conformation. Caudal fin position was then compared to muscle activity recorded by electromyography (EMG) in order to determine the role of intrinsic caudal musculature. Comparison among speeds, as well as continuous EMG while increasing swimming speed, confirmed that muscle recruitment varies significantly with speed. At 0.5 L s-1, the caudal fin was generally not used for propulsion, and swimming was accomplished primarily through body undulations. With increasing swimming speed, relative timing of muscle activity within each tail beat did not change; however, the number of muscles being used increased, as did the intensity of muscle activity. Active at 1.2 L s-1, the supracarinalis and infracarinalis muscles acted on the dorsal- and ventral-most fin rays, respectively, to expand the surface area of the caudal fin. The interradialis muscles adducted individual fin rays and propagated a wave ventrally along the edge of the caudal fin, following activation of the hypochordal longitudinalis.