Unusual aerobic performance at high temperatures in juvenile Chinook salmon, Oncorhynchus tshawytscha

Volume 5 • 2017 10.1093/conphys/cow067 Research article Unusual aerobic performance at high temperatures in juvenile Chinook salmon, Oncorhynchus tshawytscha Jamilynn B. Poletto1,†, Dennis E. Cocherell1, Sarah E. Baird1, Trinh X. Nguyen1, Valentina Cabrera-Stagno2, Anthony P. Farrell3 and Nann A. Fangue1,* Department of Wildlife, Fish and Conservation Biology, University of California, Davis, CA 95616, USA United States Environmental Protection Agency, Region 9, 75 Hawthorne Street, San Francisco, CA 94105, USA 3 Department of Zoology and Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 2 *Corresponding author: Department of Wildlife, Fish and Conservation Biology, University of California, Davis, CA 95616, USA. Tel: (530) 752-4997. Email: .............................................................................................................................................................. Understanding how the current warming trends affect fish populations is crucial for effective conservation and management. To help define suitable thermal habitat for juvenile Chinook salmon, the thermal performance of juvenile Chinook salmon acclimated to either 15 or 19°C was tested across a range of environmentally relevant acute temperature changes (from 12 to 26°C). Swim tunnel respirometers were used to measure routine oxygen uptake as a measure of routine metabolic rate (RMR) and oxygen uptake when swimming maximally as a measure of maximal metabolic rate (MMR) at each test temperature. We estimated absolute aerobic scope (AAS = MMR − RMR), the capacity to supply oxygen beyond routine needs, as well as factorial aerobic scope (FAS = MMR/RMR). All fish swam at a test temperature of 23°C regardless of acclimation temperature, but some mortality occurred at 25°C during MMR measurements. Overall, RMR and MMR increased with acute warming, but aerobic capacity was unaffected by test temperatures up to 23°C in both acclimation groups. The mean AAS for fish acclimated and tested at 15°C (7.06 ± 1.76 mg O2 kg−1 h−1) was similar to that measured for fish acclimated and tested at 19°C (8.80 ± 1.42 mg O2 kg−1 h−1). Over the entire acute test temperature range, while MMR and AAS were similar for the two acclimation groups, RMR was significantly lower and FAS consequently higher at the lower test temperatures for the fish acclimated at 19°C. Thus, this stock of juvenile Chinook salmon shows an impressive aerobic capacity when acutely warmed to temperatures close to their upper thermal tolerance limit, regardless of the acclimation temperature. These results are compared with those for other salmonids, and the implications of our findings for informing management actions are discussed. Key words: Conservation, fish, metabolic rate, metabolism, physiology, plasticity Editor: Steven Cooke Received 5 July 2016; Revised 10 November 2016; Editorial Decision 14 November 2016; accepted 16 November 2016 Cite as: Poletto JB, Cocherell DE, Baird SE, Nguyen TX, Cabrera-Stagno V, Farrell AP, Fangue NA (2017) Unusual aerobic performance at high temperatures in juvenile Chinook salmon, Oncorhynchus tshawytscha. Conserv Physiol 5(1): cow067; doi:10.1093/conphys/cow067. .............................................................................................................................................................. † Present address: University of Nebraska-Lincoln, School of Natural Resources, Lincoln, NE 68527, USA. .............................................................................................................................................................. © The Author 2017. Published by Oxford University Press and the Society for Experimental Biology. 1 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. 1 Research article Conservation Physiology • Volume 5 2017 .............................................................................................................................................................. Introduction Metabolic rate of fishes is dependent on temperature and can be assessed directly by measuring standard metabolic rate (SMR). Furthermore, as fish approach their maximal swimming capacity, they tend to increase their aerobic metabolic rate to a maximal metabolic rate (MMR). The aerobic capacity to deliver oxygen to tissues above a basic need can then be calculated from these measures [calculated either by subtracting SMR from MMR, termed absolute aerobic scope (AAS = MMR − SMR), or by dividing MMR by SMR, termed factorial aerobic scope (FAS = MMR/SMR)]. Absolute aerobic scope defines the maximal aerobic capacity available at a given temperature to perform the activities essential for survival that extend beyond routine maintenance of life to include ecologically relevant and important functions (i.e. swimming, foraging, growth, etc.; Pörtner and Knust, 2007; Pörtner and Farrell, 2008; Clark et al., 2013). However, it does not predict when or how these activities are used (Farrell, 2016). The oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis (Pörtner, 2001; Pörtner and Knust, 2007; Pörtner and Farrell, 2008) addresses this by stating that the extremes of the thermal tolerance of an animal will be determined by the aerobic metabolism of active tissues (once an animal is no longer able to supply oxygen to active tissues above a maintenance level, the animal will no longer be able to tolerate temperatures above or below this limit). The OCLTT hypothesis has emerged as a conceptual model to assess thermal performance of aquatic animals and to determine the fundamental thermal range for a particular species (Pörtner, 2001; Pörtner and Knust, 2007; Pörtner and Farrell, 2008), but not without some debate (e.g. Clark et al., 2013; Farrell, 2013; Pörtner and Giomi, 2013; Norin et al., 2014). As with many measures of physiological performance, metabolic rates and aerobic scope values are not static and can be modified by biological variables, such as ontogeny (Oikawa et al., 1991; Clarke and Johnston, 1999), or As fish populations decline (e.g. Moyle and Leidy, 1992; Moyle et al., 2011; Quiñones and Moyle, 2014) and management becomes more crucial for population persistence, knowledge of thermal limits, optimal thermal ranges, and a mechanistic understanding of how key physiological processes, such as metabolic rate, change in response to environmental variables become more important (Beitinger et al., 2000; Pörtner, 2001; Niklitschek and Secor, 2005; Horodysky et al., 2015; Martin et al., 2015; Jeffries et al., 2016; Komoroske et al., 2016). Therefore, our objective was to estimate the aerobic scope of juvenile Chinook salmon (Oncorhynchus tshawytscha) acclimated to two di (...truncated)