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Abstract
Oxygen consumption () was measured for gilthead seabream (Sparus aurata) during spontaneous and forced activities. During spontaneous activity, the swimming pattern was analysed for the effect on
on the average speed (U), turning rate (θ) and change in speed (ΔU). All swimming characteristics contributed significantly to the source of spontaneous swimming costs, and the models explained up to 58% of the variation in
Prediction of
of fish in field studies can thereby be improved if changes in speed and direction are determined in addition to swimming speed. A relationship between swimming speed and
during forced activity was also established. During spontaneous activity, 2.5 times more energy was used than in forced swimming at a speed of 0.5 BL s−1. This indicates that spontaneous swimming costs may be considerably higher compared with those of a fixed swimming speed. However, comparing
at the respective optimum swimming speeds with the lowest cost of transport (U
opt) resulted in similar values independent of swimming mode. This could be an important observation in estimating energetic costs of free-ranging fishes.
Acknowledgements
We thank Kim Ekmann and Jørgen Holm from BioMar A/S for the supply of seabream. We are grateful to Fishnet.dk, a research network financed by the Danish Agricultural and Veterinary Research Council for funding this work. The experiments comply with the Danish laws on animal ethics.