Differences in Exercise Physiology between Two Atlantic Cod (Gadus morhua) Populations from Different Environments

Abstract

Little attention has been given to the study of physiological variation within species of fish. This study examines whether a population of Atlantic cod (Gadus morhua) found in the brackish Bras d'Or Lakes of Nova Scotia, Canada, has different physiological characteristics than a nearby Atlantic ocean cod population. Chronically cannulated cod from both populations were exercised to exhaustion in a swim-tunnel respirometer. Although exercise performance was identical between populations, the physiological bases of that performance differed substantially. Cod from the Bras d'Or system had greater metabolic, ventilatory, and cardiac rates as well as a greater estimated resting metabolic rate. The Bras d'Or population used a greater proportion of anaerobic metabolism in attaining its maximal performance level as surmised from a relatively greater metabolic acid-base disturbance and higher lactate levels during recovery from exercise in the Bras d'Or population. Bras d'Or cod also had generally more dilute plasma and lower levels of hemoglobin in its erythrocytes than conspecifics from the Atlantic Ocean. These results are discussed as possible clues to the physiological adjustments necessary for cod to succeed in the Bras d'Or system.