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

As fish approach fatigue at high water velocities in a critical swimming speed (U_crit) 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 (Ṁ_O ) sampling intervals (5-20 min) tend to smooth any dynamic fluctuations in active Ṁ_O  (Ṁ_O) and thus likely underestimate the peak Ṁ_O Here, we used rainbow trout (Oncorhynchus mykiss) to explore the dynamic nature of Ṁ_O near U_crit using various sampling windows and an iterative algorithm. Compared with a conventional interval regression analysis of Ṁ_O over a 10-min period, our new analytical approach generated a 23% higher peak Ṁ_O Therefore, we suggest that accounting for such dynamics in Ṁ_O with this new analytical approach may lead to more accurate estimates of maximum Ṁ_O  in fishes.