In this study, rainbow trout was used as the experimental fish, and the dynamical swim-ming force of the fish stuck in a net was measured. The maximum swimming force was decided from a mean dynamical froce acting for four or five seconds. The maximum swimming force Fs (g) can be expressed as a function of the total length L(cm) as the following formula for rainbow trout shows:
Fs=0.00285L3 The maximum swimming speed which the fish can sustain for only four or five seconds and the maximum frequency of the tail beat under this condition were investigated using a simple hydrodynamic model, and considered on the basis of the experimental results of the maximum swimming speed. The maximum swimming speed Vmax over total length L and the maximum frequency of the tail beat Fmax independent of the fish size, can be expressed for rainbow trout as a function of total length L respectively as the following formulae show: Vmax/L=58.7/√L-23/L
Fmax=62.5/√L