Influence of experimental set-up and methodology for measurements of metabolic rates and critical swimming speed in Atlantic salmon Salmo salar.

Malthe Hvas,Frode Oppedal

doi:10.1111/jfb.14087

Abstract

In this study, swim-tunnel respirometry was performed on Atlantic salmon Salmo salar post-smolts in a 90 l respirometer on individuals and compared with groups or individuals of similar sizes tested in a 1905 l respirometer, to determine if differences between set-ups and protocols exist. Standard metabolic rate (SMR) derived from the lowest oxygen uptake rate cycles over a 20 h period was statistically similar to SMR derived from back extrapolating to zero swim speed. However, maximum metabolic rate (MMR) estimates varied significantly between swimming at maximum speed, following an exhaustive chase protocol and during confinement stress. Most notably, the mean (±SE) MMR was 511 ± 15 mg O2 kg-1 h-1 in the swim test which was 52% higher compared with 337 ± 9 mg O2 kg-1 in the chase protocol, showing that the latter approach causes a substantial underestimation. Performing group respirometry in the larger swim tunnel provided statistically similar estimates of SMR and MMR as for individual fish tested in the smaller tunnel. While we hypothesised a larger swim section and swimming in groups would improve swimming performance, Ucrit was statistically similar between both set-ups and statistically similar between swimming alone v. swimming in groups in the larger set-up, suggesting that this species does not benefit hydrodynamically from swimming in a school in these conditions. Different methods and set-ups have their own respective limitations and advantages depending on the questions being addressed, the time available, the number of replicates required and if supplementary samplings such as blood or gill tissues are needed. Hence, method choice should be carefully considered when planning experiments and when comparing previous studies.

Highlights

Whole-animal energy expenditure, termed metabolic rate and locomotory ability, are arguably two of the most important physiological traits to investigate when trying to understand the fundamental biology of fish and the range of environments and lifestyles they are adapted to
Live mass (M), and K of S. salar were statistically similar between groups, but LF was significantly lower in the chase group compared with the two groups tested in the larger swim tunnel (ANOVA, df = 68, P < 0.01; Table 1)
3.1 | Standard metabolic rate In S. salar measured in the smaller swim-tunnel respirometer, the SMR was 123 ± 4 mg O2 kg−1 h−1 when calculated as the average of the lowest 10% ṀO2 values, after removing outliers, over a c. 20 h period and 124 ± 7 mg O2 kg−1 h−1 when back extrapolating to a swim speed of zero

Summary

Introduction

Whole-animal energy expenditure, termed metabolic rate and locomotory ability, are arguably two of the most important physiological traits to investigate when trying to understand the fundamental biology of fish and the range of environments and lifestyles they are adapted to. Swim-tunnel respirometers have been designed to systematically measure the metabolic rate at different swimming speeds as well as the highest attainable swimming speeds of fish (Blažka et al, 1960; Brett, 1964; Steffensen et al, 1984). Ucrit is a measure of prolonged swimming capacity and is obtained by incrementally increasing current speeds until the fish being tested fatigues (Brett, 1964; Plaut, 2001). The aerobic scope (AS) can be calculated from the difference between SMR and MMR and is widely used to infer how fish may cope in specific environments, as the AS reflects the available aerobic capacity to perform fitness related activities (Clark et al, 2013; Farrell, 2016; Fry, 1971)

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