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 O2 ) sampling intervals (5-20 min) tend to smooth any dynamic fluctuations in active Ṁ O2  (Ṁ O2active) and thus likely underestimate the peak Ṁ O2active Here, we used rainbow trout (Oncorhynchus mykiss) to explore the dynamic nature of Ṁ O2active near U crit using various sampling windows and an iterative algorithm. Compared with a conventional interval regression analysis of Ṁ O2active over a 10-min period, our new analytical approach generated a 23% higher peak Ṁ O2active Therefore, we suggest that accounting for such dynamics in Ṁ O2active with this new analytical approach may lead to more accurate estimates of maximum Ṁ O2  in fishes.