Aerobic and anaerobic swimming performance of individual Atlantic cod

Individual Atlantic cod (Gadus morhua) were exercised using three different measures of swimming performance. (1) An endurance test (critical swimming speed, U-crit, protocol) designed to assess predominantly aerobic enduranc e swimming (duration hours). (2) An acceleration test (U-burst), in which t he fish were required to swim against a rapidly increasing current until ex hausted (duration minutes). This test was designed to assess predominantly glycolytic-based swimming capacity. (3) A sprint test that examined the ani mals' ability to swim away from a sudden stimulus (duration seconds). Rates of oxygen consumption ((M) over dot O-2) during the endurance test and var ious morphological variables of the individual fish were also measured. Bot h aerobic and anaerobic swimming performance of individual cod were found t o be significantly repeatable over a 3 month period. (M) over dot O-2 durin g the U-crit protocol was also significantly repeatable at intermediate to high swimming speeds, but not at low speeds. Our results support extrapolat ion from metabolic rates at incremented swimming speeds to zero activity as the best way to measure standard metabolic rate in cod, While performance in the U-crit test and the sprint test were positively correlated, there wa s a negative correlation between performance in the U-crit test and perform ance in the U-burst test. This implies a potential trade-off in individual cod between stamina and the ability to use glycolytic-based locomotion. Int er-individual variation in swimming performance during these protocols, whi le substantial, was not correlated with individual variation in fin surface areas, age or morphology, However, U-burst performance was dependent upon the sex of the animals, while performance during the U-crit protocol was si gnificantly correlated with their aerobic scope for activity.