CHADWELL, BA*; VICHOT, D; HARRIS, C; ASHLEY-ROSS, MA; Wake Forest University; Wake Forest University; Wake Forest University; Wake Forest University: Dorsal fin use during the escape response in largemouth bass (Micropterus salmoides).

Though the fast-start escape response in fish is powered primarily by the axial musculature, the median fins are in a position to increase the body depth and thus enhance lateral thrust during the behavior. We quantified kinematics and electromyographic (EMG) activity in axial and dorsal fin muscles during the escape response in largemouth bass. Recordings were made from 6 fish; all exhibited the stereotypical C-start. Movement began an average of 12.1 ms following the startle stimulus; stage 1 lasted an average of 37.8 ms. In undisturbed bass, the spiny dorsal fin is depressed against the body while the soft dorsal fin is semi-elevated. Both fins are erected during stage 1, and have reached full elevation by the beginning of stage 2, supporting the hypothesis that dorsal fins are deployed to increase lateral thrust at the start of stage 2. EMG recordings revealed that axial and dorsal fin muscles became active nearly simultaneously. Dorsal fin muscles on both sides of the body activated synchronously, presumably to erect the fins while minimizing lateral deflection. Most muscles showed multiple discrete bursts of activity during the escape response.