S1-2.3 Jan. 4 Finfull thoughts: does pelvic oscillation influence anal fin action in fishes? STANDEN, E.M.; Harvard University email@example.com
Fish must balance torques around their centre of mass to control their body position. Recent kinematic and hydrodynamic studies on trout median fins show that dorsal and anal fins in trout appear to produce forces that balance rolling torques during swimming. Dorsal and anal fins oscillate with a large phase lag, yet the lateral jets produced by the fins have a small phase lag. This means fins release their jets at a similar time but at different points in their oscillation cycle. Dorsal fins release jets after they reach maximum excursion and anal fins before maximum excursion. Differences in incident flow experienced by each fin may contribute to different jet release timings between fins. Trout have two sets of paired fins located upstream of the median fins. The ventral location of paired fins means that the wake they produce could influence the flow surrounding the ventral anal fin. To date the kinematic or hydrodynamic function of the posterior paired pelvic fins has not been described. In this study I use particle imaging velocimetry and high-speed cameras to visualize the wake structures and kinematics of the pelvic fins in brook trout (Salvelinus fontinalis). I use a horizontal light sheet to visualize the entire fish belly and describe how the pelvic fin wake interacts with the anal fin during swimming. Trout oscillate their pelvic fins in phase with the tail beat cycle, one fin abducting while the contralateral fin adducts. The contralateral oscillation of the pelvic fins produces distinct lateral jets that appear to influence and contribute to the anal fin wake structure, possibly enhancing anal fin hydrodynamic function.