Swimming performance, maximum O2 consumption, EPOC, post-exercise recovery, and tissue metabolites after fatigue by <i>U</i> crit <i>versus</i> chase protocols in mahi-mahi ( <i>Coryphaena hippurus</i> ), a high-performance pelagic teleost

Carangiform fishes are highly active pelagic teleosts, but there have been relatively few studies of their swimming physiology. Recent evidence in other species suggests that swimming to exhaustion using a critical swimming speed (Ucrit) protocol may yield higher maximum O2 consumption rates (ṀO2max) than chase methodologies. However, there has been little work comparing the internal physiological disturbances and recovery processes resulting from the two methods. We compared these two protocols in young adult mahi-mahi (∼254 g, 26°C, 32 ppt). ṀO2maxafter chasing (20 min) was 30% lower than during Ucrit swimming (20-min speed increments). Absolute and factorial aerobic scopes were 42% and 30% lower, respectively, by chasing. Post-exercise recovery was much slower in chased fish, a > 1.8-fold higher excess post-exercise O2 consumption (EPOC) than in Ucrit fish. 60% of the total O2 cost of swimming to fatigue in the Ucrit protocol was incurred during swimming (i.e., extra ṀO2 above resting O2 consumption rate (ṀO2rest) and 40% during recovery (i.e., EPOC). Tissue-specific profiles of metabolites were very different between the two protocols, with the Ucrit treatment causing greater lactate accumulation in red muscle, and chasing causing greater lactate accumulation in the liver and intracellular pH (pHi) depression in both the red and white muscle at exhaustion, with other differences during recovery. Overall, the results suggest a much greater anaerobic contribution to exercise metabolism caused by chasing. The two protocols yield vastly different results, reflecting different processes. We conclude that the Ucrit protocol provides a much better profile of aerobic capacity.