Partition of aerobic and anaerobic swimming costs related to gait transitions in a labriform swimmer

Members of the family Embiotocidae exhibit a distinct gait transition from exclusively pectoral fin oscillation to combined pectoral and caudal fin propulsion with increasing swimming speed. The pectoral-caudal gait transition occurs at a threshold speed termed U(p-c). The objective of this study was to partition aerobic and anaerobic swimming costs at speeds below and above the U(p-c) in the striped surfperch Embiotoca lateralis using swimming respirometry and video analysis to test the hypothesis that the gait transition marks the switch from aerobic to anaerobic power output. Exercise oxygen consumption rate was measured at 1.4, 1.9 and 2.3 L s(-1). The presence and magnitude of excess post-exercise oxygen consumption (EPOC) were evaluated after each swimming speed. The data demonstrated that 1.4 L s(-1) was below the U(p-c), whereas 1.9 and 2.3 L s(-1) were above the U(p-c). These last two swimming speeds included caudal fin propulsion in a mostly steady and unsteady (burst-assisted) mode, respectively. There was no evidence of EPOC after swimming at 1.4 and 1.9 L s(-1), indicating that the pectoral-caudal gait transition was not a threshold for anaerobic metabolism. At 2.3 L s(-1), E. lateralis switched to an unsteady burst and flap gait. This swimming speed resulted in EPOC, suggesting that anaerobic metabolism constituted 25% of the total costs. Burst activity correlated positively with the magnitude of the EPOC. Collectively, these data indicate that steady axial propulsion does not lead to EPOC whereas transition to burst-assisted swimming above U(p-c) is associated with anaerobic metabolism in this labriform swimmer.