Warming, but not acidification, increases metabolism and reduces growth of redfish (Sebastes fasciatus) in the Gulf of St. Lawrence.

Understanding the effects of global change, including temperature, pH, and oxygen availability, on commercially important species is crucial for anticipating consequences for these resources and their ecosystems. In the Gulf of St. Lawrence (GSL), redfish (Sebastes spp.) were under moratorium from 1995 to 2023, but the fishery has reopened in 2024 following massive recruitment observed in 2011–2013. Despite current high abundance, little is known about their metabolic and thermal physiology. To address this, we quantified the effects of four acclimatation temperatures (2.5, 5.0, 7.5, and 10.0 °C) and two ocean acidification scenarios (current and future) on standard and maximum metabolic rates (SMR and MMR), aerobic scope (AS), factorial aerobic scope, hypoxia tolerance (O2crit), food consumption, growth and food conversion efficiency (FCE) in redfish (Sebastes fasciatus Storer, 1854). SMR, MMR, and AS increased with temperature, but growth and FCE decreased with temperature, likely due to increased cost of maintenance. Food consumption was lower at 2.5 °C, but similar at higher temperatures. Redfish were less hypoxia-tolerant at higher temperatures. Except for SMR, no significant effect of pH was observed. These results suggest that future changes in the GSL will challenge redfish, with potential long-term effects on growth due to increased energy requirements.