Finding the peak of dynamic oxygen uptake during fatiguing exercise in fish

Abstract

As fish approach fatigue at high water velocities in a critical swimming speed (Ucrit) test, their swimming mode and oxygen cascade typically move to an unsteady state because they adopt an unsteady, burst-and-glide swimming mode despite a constant, imposed workload. However, conventional rate of oxygen uptake (M_O2) sampling intervals (5–20 min) tend to smooth any dynamic fluctuations in active M_O2 (M_O2active) and thus likely underestimate the peak M_O2active. Here, we used rainbow trout (Oncorhynchus mykiss) to explore the dynamic nature of M_O2active near Ucrit using various sampling windows and an iterative algorithm. Compared with a conventional interval regression analysis of M_O2active over a 10-min period, our new analytical approach generated a 23% higher peak M_O2active. Therefore, we suggest that accounting for such dynamics in M_O2active with this new analytical approach may lead to more accurate estimates of maximum M_O2 in fishes.