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

Abstract

This study hypothesized that oxygen uptake (ṀO 2) measured with a novel protocol of chasing rainbow trout Oncorhynchus mykiss to exhaustion inside a static respirometer while simultaneously monitoring ṀO 2 (ṀO 2chase) would generate the same and repeatable peak value as when peak active ṀO 2 (ṀO 2active) is measured in a critical swimming speed protocol. To reliably determine peak ṀO 2chase , and compare to the peak during recovery of ṀO 2 after a conventional chase protocol outside the respirometer (ṀO 2rec), 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 ṀO 2) to account for ṀO 2 dynamics. In support of this hypothesis, peak ṀO 2active (707 ± 33 mg O 2 h −1 kg −1) and peak ṀO 2chase (663 ± 43 mg O 2 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 ṀO 2max can be independent of whether a fish is exhaustively chased inside a respirometer or swum to fatigue in a swim tunnel, provided ṀO 2 is analysed with an iterative algorithm and a minimum but reliable sampling window. The importance of using this analytical approach was illustrated by peak ṀO 2chase 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 ṀO 2chase was 18% higher (P < 0.05) than peak ṀO 2rec , chasing a fish inside a static respirometer may be a better protocol for obtaining maximum ṀO 2 .

Guidelines for reporting methods to estimate metabolic rates by aquatic intermittent-flow respirometry

“…in seconds, after the cessation of exercise) was also often not provided (criterion 44). This is important because data processing procedures can bias estimates of MMR (Zhang et al, 2020), including the duration of the slope used to estimate MMR and the specific method of determining the maximum rate of oxygen uptake during recovery after exercise (criterion 49). Our survey revealed that both criteria were relatively underreported but, given emerging awareness of their importance, it is vital that authors provide these details going forward.…”

Analytical methods matter too: Establishing a framework for estimating maximum metabolic rate for fishes

“…Individuals were fed to satiation every 3-5 days using human-grade market squid (Doryteuthis opalescens) and mackerel (Scomber japonicus) and were fasted for a minimum of 48 hr before experiments to remove the influence of specific dynamic action on metabolic rate estimates. Experimental conditions for Rainbow Trout and Atlantic Salmon can be found in Zhang et al (2016Zhang et al ( , 2020, respectively.…”

“…All experiments were carried out using a chase-to-exhaustion protocol where each individual was manually chased by hand in a tank large enough to allow unimpeded burst-swimming Zhang et al, 2016Zhang et al, , 2020. The focal individual was deemed exhausted once it stopped bursting away and began resting on the bottom of the chase tank between stimuli (usually after 4-7 min of chasing).…”

Hypoxia Performance Curve: Assess a Whole-Organism Metabolic Shift from a Maximum Aerobic Capacity towards a Glycolytic Capacity in Fish

“…Of greater concern is that chasing a fish outside of a respirometer potentially underestimatesṀO 2max [88] and so this problem has been avoided by adding a simple chasing device to a standard respirometry chamber (Figure 3d). This way a fish can be agitated to generate a reliableṀO 2peak [88] and even repeatedly agitated without having to remove the fish from the respirometer. while it is continuously agitated for 15 min inside a respirometer (ṀO 2chase ) at normoxia (>80% air sat.).…”

“…Maintaining the chasing apparatus at the same DO as the respirometer would be another challenge. Of greater concern is that chasing a fish outside of a respirometer potentially underestimates Ṁ O 2max [ 88 ] and so this problem has been avoided by adding a simple chasing device to a standard respirometry chamber ( Figure 3 d). This way a fish can be agitated to generate a reliable Ṁ O 2peak [ 88 ] and even repeatedly agitated without having to remove the fish from the respirometer.…”