CARROLL, Andrew; UC Davis: Muscle function during suction feeding in the largemouth bass, Micropterus salmoides.

Activation and strain in the sternohyoideus (SH) were measured in vivo in five largemouth bass, Micropterus salmoides. The SH is thought to actuate lower jaw depression, hyoid depression, and suspensorial abduction during suction feeding in teleost fish. Sonomicrometry was used to measure fascicle shortening and lower jaw kinematics, while activity was measured by electromyography (EMG). In three fish SH fascicles consistently shortened during fast lower jaw depression, but in two individuals they contracted isometrically or lengthened slightly during fast lower jaw depression. The SH continued shortening after peak gape, presumably actuating hyoid depression and lateral expansion of the buccal cavity. Onset of SH re-lengthening and onset lower jaw elevation were simultaneous, as were the return of the SH to resting length and gape closure. SH fascicles reached sustained shortening velocities averaging �2.5 fascicle lengths per second, and generally increased shortening velocity after peak gape. Epaxial strain was investigated in some fish and was found to contract at similar length specific shortening velocities. These shortening velocities suggest that the suction feeding muscles actively shorten to generate power during suction feeding. Muscular power production may limit the speed of cranial expansion, thereby limiting suction feeding performance on evasive prey. Musculoskeletal morphologies that allow maximal muscular power production may be necessary for suction feeding on evasive prey. The implications of this putative limitation as a tool to interpret fish musculoskeletal morphology are discussed.