94.4 Saturday, Jan. 7 Pectoral girdle motion and hypaxial muscle strain during suction feeding in largemouth bass, Micropterus salmoides CAMP, A.L.*; BRAINERD, E.L.; Brown University, Providence, RI; Brown University, Providence, RI firstname.lastname@example.org
To capture food in an environment 900 times as dense as air, fish rely on suction: explosively expanding the mouth cavity to accelerate fluid and engulf prey. This wave of expansion originates dorsally with cranial elevation and ventrally with hyoid depression. Both mechanisms require substantial muscle power, but the cranial muscles are relatively small. Instead, power may come from the large body muscles, epaxialis (EP) and hypaxialis (HYP). The rostral EP is already known to power dorsal expansion. The HYP may be stabilizing the pectoral girdle while the sternohyoideus muscle retracts and depresses the hyoid. Alternatively, the HYP could power ventral expansion by retracting the pectoral girdle, which is connected to the hyoid by the sternohyoideus. We tested the role of the HYP in ventral expansion, and the rostrocaudal extent of shortening in EP and HYP during feeding. Using suction strikes of largemouth bass (Micropterus salmoides), we measured neurocranial and pectoral girdle kinematics with X-ray Reconstruction of Moving Morphology (XROMM). XROMM quantifies 3D skeletal motion from bone models and bi-planar high-speed fluoroscopy. From these x-ray videos, we also measured the distances between intramuscular markers to calculate muscle strain in the EP, HYP, and sternohyoideus. Surprisingly, HYP strain magnitudes are statistically significantly greater than EP (mean of 5.8% versus 3.7%; p<0.01). The HYP shortens a statistically significantly greater distance than sternohyoideus (mean of 5.7mm versus 0.66mm, p<0.001), and the pectoral girdle is retracted; both results support the HYP as powering ventral expansion. The EP and HYP show strain as far caudal as the second dorsal fin, suggesting these body muscles are powering suction feeding.