Abstract
By understanding range-wide intraspecific variation in metabolic rate we can better understand how organisms have adapted to their environment. However, methods to quantify metabolic rate of fishes from remote areas or those that cannot be brought back to the laboratory because of imperilment status are lacking. Consequently, practical and reliable field-based methods are needed. To address this need, we developed a simple yet robust intermittent-flow respirometry system, adapted from a design commonly used in the laboratory that is readily suited for field use. Standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS) estimates were obtained from juvenile lake trout (Salvelinus namaycush) and brook trout (Salvelinus fontinalis) using both field- and laboratory-based systems. Whole-fish SMR, MMR and AS estimates from the field and laboratory methods did not differ from one another (ANCOVA and LMM: all P > 0.05) for either species and were comparable to estimates previously reported. Our field setup is a simpler system than the conventional laboratory-based system that requires less power and equipment to operate, yet still offers users the ability to: (1) acclimate fish to the respirometry chamber; (2) measure oxygen consumption during a shorter period (1 h), which yield metabolic rate estimates comparable to systems that take measurements over longer periods; and (3) take repeated oxygen consumption measurements with manual user-defined flush and measurement phase routines. Developing practical and reliable field respirometry methods, as demonstrated here, is important if we wish to improve our ability to predict how imperiled species will respond to changes in their environment. Such knowledge is critical for informing conservation strategies.
Highlights
A long-standing and common method of understanding the physiological capacity of fish is to estimate their metabolic rate—the rate at which an organism assimilates, transforms and expends energy (Fry and Hart, 1948; Brett, 1962; Beamish, 1964)
The slope of the relationship between the calculated metabolic rate metrics (SMR, maximum metabolic rate (MMR) and aerobic scope (AS)) and fish body mass did not differ between treatments (SMR-Mass × Treatment: F1,15 = 0.343, P = 0.566; MMR-Mass × Treatment: F1,15 = 1.04, P = 0.324; AS-Mass × Treatment: F1,15 = 0.901, P = 0.358) and the intercept of Standard metabolic rate (SMR), MMR and AS values estimated by each treatment did not differ (SMR-Treatment: F1,16 = 0.979, P = 0.337; MMR-Treatment: F1,16 = 0.007, P = 0.931; AS- Treatment: F1,16 = 0. 048, P = 0.829)
These results indicate that the metabolic rate metrics did not differ among respirometry methods
Summary
A long-standing and common method of understanding the physiological capacity of fish is to estimate their metabolic rate—the rate at which an organism assimilates, transforms and expends energy (Fry and Hart, 1948; Brett, 1962; Beamish, 1964). Metabolic rate is regarded as the fundamental biological process that governs an organism’s survival (Brown et al, 2004) and is often estimated in fish using whole-animal respirometry (Svendsen et al, 2016) This method uses the oxygen consumption (M O2) of an organism over time in an enclosed vessel as an indirect measure of metabolic rate. Many populations that have adapted to novel environments are found at range margins (Sexton et al, 2009), often in remote areas (e.g. Arctic), which precludes use of conventional laboratory-based respirometry In these situations a reliable field respirometry system would improve our capacity to conduct similar studies
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