CHADWELL, B.A.*; HUTCHESON, J.L.; ASHLEY-ROSS, M.A.; Wake Forest University; Wake Forest University; Wake Forest University: Changing the shape of things: Elevating the median fins alters the lateral profile of largemouth bass (Micropterus salmoides).

Based on a hydrodynamic model, it has been hypothesized that fish with larger median fins at the tail should show enhanced fast-start performance. While there is supporting evidence, very few studies have approached the subject in great depth and how median fins contribute to performance is unclear. To address this question, we have begun what we hope to be comprehensive studies of the role median fins play in the escape response of fish, using the largemouth bass as a baseline model. We had previously studied the pattern of median fin recruitment during the bass escape response and found that fin elevation coincided with the onset of forward propulsion. In this paper, we present the change in lateral profile of bass when median fins are relaxed vs. elevated. Post-mortem, whole bass were digitally photographed with median fins relaxed and maximally elevated. Lateral surface area (LSA) for the entire fish as well as each median fin [spiny dorsal (spD), soft dorsal (sfD), anal (An) and caudal (Cd)] were measured using imaging software. Median fins increased the body LSA by 120% when relaxed and 143% when elevated, an increase by a factor of 1.2. In both positions, individual fin contribution to the LSA of the body followed the same pattern: Cd>>sfD>An>>spD. However, the increase in fin LSA followed a reverse pattern: spD>>An>sfD>Cd. Along the length of the fish, the greatest increase of lateral depth occurred posterior to the center of mass, i.e. at the tail. These findings support our hypothesis that elevation of the median fins increases the lateral profile of the bass, particularly at the tail, and could potentially enhance performance of the escape response.