Measuring maximum oxygen uptake with an incremental swimming test and by chasing rainbow trout to exhaustion inside a respirometry chamber yields the same results.

This study hypothesized that oxygen uptake (MO2 ) measured with a novel protocol of chasing rainbow trout Oncorhynchus mykiss to exhaustion inside a static respirometer while simultaneously monitoring MO2 (MO2chase ) would generate the same and repeatable peak value as when peak active MO2 (MO2active ) is measured in a critical swimming speed protocol. To reliably determine peak MO2chase , and compare to the peak during recovery of MO2 after a conventional chase protocol outside the respirometer (MO2rec ), this study applied an iterative algorithm and a minimum sampling window duration (i.e., 1 min based on an analysis of the variance in background and exercise MO2 ) to account for MO2 dynamics. In support of this hypothesis, peak MO2active (707 ± 33 mg O2 h-1 kg-1 ) and peak MO2chase (663 ± 43 mg O2 h-1 kg-1 ) were similar (P = 0.49) and repeatable (Pearson's and Spearman's correlation test; r ≥ 0.77; P < 0.05) when measured in the same fish. Therefore, estimates of MO2max can be independent of whether a fish is exhaustively chased inside a respirometer or swum to fatigue in a swim tunnel, provided MO2 is analysed with an iterative algorithm and a minimum but reliable sampling window. The importance of using this analytical approach was illustrated by peak MO2chase being 23% higher (P < 0.05) when compared with a conventional sequential interval regression analysis, whereas using the conventional chase protocol (1-min window) outside the respirometer increased this difference to 31% (P < 0.01). Moreover, because peak MO2chase was 18% higher (P < 0.05) than peak MO2rec , chasing a fish inside a static respirometer may be a better protocol for obtaining maximum MO2 .