Interrelationship among temperature, metabolism, swimming performance and recovery in Pacific cod (Gadus macrocephalus): implications of a changing climate

Abstract

Physiological constraints are suggested to contribute to the observed changes in relative abundance of Pacific cod (Gadus macrocephalus) seen in association with interdecadal changes in sea surface temperatures. To examine this concept, two experiments were conducted to determine critical swimming speed (Ucrit), rates of oxygen consumption and recovery post-exhaustion of adult cod acclimated to different temperatures. In addition, hematocrit and plasma concentrations of cortisol, metabolites and ions from resting and exhausted fish were measured to assess the impact of swim trials on fish condition. In experiment one, fish acclimated to 4°C had similar mean Ucrit (1.07 BL/s) and resting metabolic rates (35.34 mg O₂/kg⁰⁸/hr) compared to fish acclimated to 11°C fish (1.07 BL/s; 49.43 mg O₂/kg⁰⁸/hr). Similarly, concentrations of blood constituents differed little between temperature treatments; each exhibited increases in plasma cortisol and metabolites from pre- to post-swim. Experiment two illustrated few differences in rates of recovery between temperature groups (2 and 7°C). After four hours of recovery there was no evidence of plasma cortisol or metabolites returning to pre-swim concentrations in either temperature group. It seems unlikely that physiological constraints on the metabolic performance of adult Pacific cod contribute to changes in their relative abundance.