title: Selection for upper thermal tolerance in rainbow trout (Oncorhynchus mykiss Walbaum).
abstract: Rainbow trout (Oncorhynchus mykiss Walbaum) in southern Western Australia have undergone passive selection for over 19 generations to survive high water temperatures. Based on the conceptual model of 'oxygen- and capacity-limited thermal tolerance', we measured critical thermal maximum (CTmax), maximum heart rate (fH,max) and aerobic scope to test the hypothesis that these rainbow trout can maintain aerobic scope at high temperatures through a robust cardiac performance supporting oxygen delivery. Across five family groups CTmax averaged 29.0±0.02°C. Aerobic scope was maximized at 15.8±0.3°C (Topt), while the upper pejus temperature (Tpej, set at 90% of maximum aerobic scope) was 19.9±0.3°C. Although aerobic scope decreased at temperatures above Topt, the value at 25°C remained well over 40% of the maximum. Furthermore, pharmacologically stimulated fH,max increased with temperature, reaching a peak value between 23.5±0.4 and 24.0±0.4°C (Tmax) for three family groups. The Arrhenius breakpoint temperature (TAB) for fH,max was 20.3±0.3 to 20.7±0.4°C, while the average Q10 breakpoint temperature (TQB, when the incremental Q10<1.6) for fH,max was 21.6±0.2 to 22.0±0.4°C. Collectively, fH,max progressively became less temperature dependent beyond 20°C (TAB and TQB), which coincides with the upper Tpej for aerobic scope. Although upper thermal performance indices for both aerobic scope and fH,max were compared among family groups in this population, appreciable differences were not evident. Compared with other populations of rainbow trout, the present assessment is consistent with the prediction that this strain has undergone selection and shows the ability to tolerate higher water temperatures.
authors.affiliation: Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada V6T 1Z4 czq2007hlj@gmail.com.
authors.forename: Zhongqi
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Fisheries, Government of Western Australia, Research Division, PO Box 20, North Beach, Western Australia 6920, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Snow
authors.affiliation: Department of Fisheries, Government of Western Australia, Research Division, PO Box 20, North Beach, Western Australia 6920, Australia School of Animal Biology - Aquaculture & Native Fish Breeding Laboratory, The University of Western Australia, 1 Underwood Avenue, Shenton Park, Western Australia 6008, Australia.
authors.forename: Craig S
authors.initials: CS
authors.lastname: Lawrence
authors.affiliation: Department of Fisheries, Government of Western Australia, Pemberton Freshwater Research Centre, Pump Hill Road, Pemberton, Western Australia 6260, Australia.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Church
authors.affiliation: Columbia River Inter-Tribal Fish Commission, 3059F National Fish Hatchery Road, Hagerman, ID 83332, USA.
authors.forename: Shawn R
authors.initials: SR
authors.lastname: Narum
authors.affiliation: Center for Aquaculture and Environmental Research, Fisheries and Oceans Canada, 4160 Marine Drive, West Vancouver, British Columbia, Canada V7V 1N6.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Devlin
authors.affiliation: Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada V6T 1Z4 Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, British Columbia, Canada V6T 1Z4.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Farrell
mesh_terms: D000064:Acclimatization; D000818:Animals; D006339:Heart Rate / Q000502:physiology; D006358:Hot Temperature; D017686:Oncorhynchus mykiss / Q000502:physiology*; D010101:Oxygen Consumption; D014904:Western Australia
keywords: Aerobic scope; Critical thermal maximum; Heart rate; Metabolic rate; Temperature tolerance; Thermal adaptation