Meeting Abstract
Ray-finned fishes exhibit tremendous variation in their mouth-size and body-shape, yet most capture food by suction feeding. In one species, largemouth bass, the power for suction expansion comes almost exclusively from the body muscles, as even the largest of the cranial expansion muscles, the sternohyoideus, produces negligible power. However, it is unclear if axial muscles power suction feeding in most fishes, or if this is limited to bass-like fish with large mouths, fusiform bodies, and a relatively small sternohyoideus muscle. Bluegill sunfish (Lepomis macrochirus) are a good test-case, as they are in the same family as largemouth bass (Centrarchidae), but have a small mouth, a tall and laterally-compressed body, and a relatively large sternohyoideus muscle. To determine the role of axial muscles during suction expansion in sunfish, we measured in vivo muscle shortening and skeletal kinematics using fluoromicrometry and X-Ray Reconstruction of Moving Morphology (XROMM). In sunfish, the epaxial muscles shortened to elevate the neurocranium and the hypaxial muscles shortened to retract the pectoral girdle during suction feeding. Like largemouth bass, sunfish used large regions of their axial muscles, extending nearly halfway down the body, to generate power during suction feeding. However, in sunfish the sternohyoideus muscle also shortened and contributed power to suction feeding, whereas it functions like a ligament in largemouth bass. These results highlight the multiple roles of the sternohyoideus in suction feeding, and suggest that the relatively powerful strikes of sunfish (compared to their body size) may require both cranial and axial muscle power.
