title: Calorespirometry reveals that goldfish prioritize aerobic metabolism over metabolic rate depression in all but near-anoxic environments.
abstract: Metabolic rate depression (MRD) has long been proposed as the key metabolic strategy of hypoxic survival, but surprisingly, the effects of changes in hypoxic O2tensions (PwO2) on MRD are largely unexplored. We simultaneously measured the O2consumption rate (ṀO2) and metabolic heat of goldfish using calorespirometry to test the hypothesis that MRD is employed at hypoxicPwO2values and initiated just belowPcrit, thePwO2below whichṀO2is forced to progressively decline as the fish oxyconforms to decreasingPwO2Specifically, we used closed-chamber and flow-through calorespirometry together with terminal sampling experiments to examine the effects ofPwO2and time onṀO2, metabolic heat and anaerobic metabolism (lactate and ethanol production). The closed-chamber and flow-through experiments yielded slightly different results. Under closed-chamber conditions with a continually decreasingPwO2, goldfish showed aPcritof 3.0±0.3 kPa and metabolic heat production was only depressed atPwO2between 0 and 0.67 kPa. Under flow-through conditions withPwO2held at a variety of oxygen tensions for 1 and 4 h, goldfish also initiated MRD between 0 and 0.67 kPa but maintainedṀO2to 0.67 kPa, indicating thatPcritis at or below thisPwO2Anaerobic metabolism was strongly activated atPwO2≤1.3 kPa, but only used within the first hour at 1.3 and 0.67 kPa, as anaerobic end-products did not accumulate between 1 and 4 h exposure. Taken together, it appears that goldfish reserve MRD for near-anoxia, supporting routine metabolic rate at sub-PcritPwO2values with the help of anaerobic glycolysis in the closed-chamber experiments, and aerobically after an initial (<1 h) activation of anaerobic metabolism in the flow-through experiments, even at 0.67 kPaPwO2.
authors.affiliation: Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, BC, Canada V6T 1Z4 regan@zoology.ubc.ca.
authors.forename: Matthew D
authors.identifier: 0000-0001-9341-5747
authors.initials: MD
authors.lastname: Regan
authors.affiliation: Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, BC, Canada V6T 1Z4.
authors.forename: Ivan S
authors.initials: IS
authors.lastname: Gill
authors.affiliation: Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, BC, Canada V6T 1Z4.
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Richards
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D000818:Animals; D001481:Basal Metabolism; D000431:Ethanol / Q000032:analysis / Q000378:metabolism; D029941:Fish Proteins / Q000097:blood / Q000378:metabolism; D006054:Goldfish / Q000097:blood / Q000502:physiology*; D006454:Hemoglobins / Q000032:analysis / Q000378:metabolism; D019344:Lactic Acid / Q000032:analysis / Q000378:metabolism; D010100:Oxygen / Q000097:blood / Q000378:metabolism*; D010101:Oxygen Consumption
chemical_list: D029941:Fish Proteins; D006454:Hemoglobins; D019344:Lactic Acid; D000431:Ethanol; D010100:Oxygen
keywords: Calorespirometry; Critical oxygen tension; Environmental hypoxia; Fish; Metabolic depression; Metabolic heat