Development and testing of a simple field-based intermittent-flow respirometry system for riverine fishes

Volume 5 • 2017 10.1093/conphys/cox048 Toolbox Development and testing of a simple field-based intermittent-flow respirometry system for riverine fishes Neil J. Mochnacz1,2,*, Benjamin C. Kissinger1, David Deslauriers1, Matthew M. Guzzo1, Eva C. Enders2, W. Gary Anderson1, Margaret F. Docker1, Dan J. Isaak3, Travis C. Durhack1 and Jason R. Treberg1,4 1 University of Manitoba, Department of Biological Sciences, Winnipeg, MB, Canada R3T 2N2 Fisheries and Oceans Canada, Winnipeg, MB, Canada R3T 2N6 3 United States Forest Service, Boise, ID, United States 83702 4 University of Manitoba, Department of Human Nutritional Sciences, Winnipeg, MB, Canada R3T 2N2 2 *Corresponding author: University of Manitoba, Department of Biological Sciences, Winnipeg, MB, Canada R3T 2N2. Email: neil.mochnacz@ dfo-mpo.gc.ca .............................................................................................................................................................. 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. Key words: Brook trout, field respirometry, metabolic rate Editor: Steven Cooke Received 20 October 2016; Revised 30 June 2017; Editorial Decision 10 July 2017; accepted 22 August 2017 Cite as: Mochnacz NJ, Kissinger BC, Deslauriers D, Guzzo MM, Enders EC, Anderson WG, Docker MF, Isaak DJ, Durhack TC, Treberg JR (2017) Development and testing of a simple field-based intermittent-flow respirometry system for riverine fishes. Conserv Physiol 5(1): cox048; doi:10.1093/conphys/cox048. .............................................................................................................................................................. .............................................................................................................................................................. © Her Majesty the Queen in Right of Canada, as represented by the Minister of Fisheries and Oceans Canada, 2017. 1 Toolbox Conservation Physiology • Volume 5 2017 .............................................................................................................................................................. Introduction 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 (ṀO2) of an organism over time in an enclosed vessel as an indirect measure of metabolic rate. Although ṀO2 has previously been measured in the field using respirometry, these systems are often very similar to those used in laboratory situations—i.e. the laboratory is brought to the field and measurements are taken (Farrell et al. 2003; Rodnick et al., 2004). These methods may be feasible for locations with road access (Farrell et al. 2003; Rodnick et al., 2004); however, in remote locations where logistical constraints (e.g. helicopter-only access) limit the overall size and weight of systems that can be used, a simpler, smaller and less energy consumptive system is required. Recently, laboratory-based respirometry has been used to examine intraspecific variability in aerobic scope (AS) of salmonids (Farrell et al., 2008; Eliason et al., 2011, 2013), where AS is defined as the capacity of a fish to deliver additional oxygen to organs to complete activities beyond those required for existence (Farrell et al., 2009). One calculates AS by subtracting the metabolic rate of a non-digesting, quiescent fish (i.e. standard metabolic rate; SMR), from the maximum metabolic rate (MMR)—typically taken from fish that are exhausted after a prolonged swimming bout (Clarke et al., 2013). These studies provided a mechanistic understanding of how Pacific salmon populations may respond to different thermal regimes. Unfortunately, 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. Here, we describe a field-based intermittent-flow respirometry system that is a simplification of a common design used in the laboratory. The aim was to develop a practical system that works within the constraints often encountered in remote field conditions, yet yields reliable and consistent measurements comparable to a commonly used laboratory system. The design of the respirometer is described and its use is demonstrated with juvenile lake trout (Salvelinus namaycush) and brook trout (Salvelinus fontinalis) in a controlled laboratory setting. Using a two-phased approach, we first tested the field prototype on lake trout to assess the feasibility of this method, and then refined the system by adding a mixing device during the measurement period and conducted a second experiment to test the new field system on brook trout. This approach was employe (...truncated)