Mechanical efficiency of fish thrust induced by tail beating: comparison between kinetic energy and metabolic energy

There are few studies that compare thrust power PT induced by tail beating with net metabolic power Pnet obtained from oxygen consumption and mechanical efficiency η (= PT Pnet ) of fish thrust. In this study, PT and Pnet were obtained using two species of chub mackerel and Japanese dace, and η was calculated by comparing kinetic energy and metabolic energy. PT was calculated by multiplying swimming speed Vswim and thrust force T obtained using two calculation methods, the Milne–Thomson principle and Kutta–Joukowski theorem. Comparing each value, η showed a certain ratio irrespective of fish species and swimming speed. Linear approximation resulted in PT = 0.21 Pnet for Milne– Thomson and PT = 0.44 Pnet for Kutta–Joukowski.