Northern squawfish Ptychochelius oregonensis, O2 consumption rate: Effects of temperature and body size

Northern squawfish, Ptychocheilus oregonensis (live weight range 0.361–1.973 kg), O₂consumption was measured with temperature-controlled, flow-through respirometers for >24 h. Mean standard O₂ consumption rate of northern squawfish increased with acclimation temperature: 24.3, 49.1, 75.0, and 89.4 mg∙kg^−0.67∙h⁻¹ at 9, 15, 18, and 21 °C, respectively. Q₁₀analysis showed that O₂ consumption rate temperature sensitivity was greatest at the intermediate acclimation temperatures (15–18 °C, Q₁₀ = 4.10), moderate at the lower acclimation temperatures (9–15 °C, Q₁₀ = 3.23), and lowest at the higher acclimation temperatures (18–21 °C, Q₁₀ = 1.80). Overall Q₁₀ was 2.96 (9–21 °C). Body size (W, grams) and temperature (T, degrees Celcius) were related to O₂ consumption (, grams per gram per day) by W^−0.285∙e^0.105T. Northern squawfish red to white muscle ratios significantly exceeded those of rainbow trout, Oncorhynchus mykiss, in cross sections at 50 and 75% of standard length. High metabolic rates and red to white muscle ratios argue for comparability of northern squawfish with active predators such as sympatric rainbow trout.