The mathematical models for the performance of aquatic animals developed by M Lighthill are compared with the experimental performance of a biomimetic fish. The equations developed by Lighthill are evaluated at steady-state conditions. Equilibrium velocity and mechanical efficiency are calculated using Lighthill's mathematical model and compared with experimental results. In both cases, a pattern is found wherein an optimum combination of tail frequency and amplitude maximizes equilibrium velocity. Differences between the theoretical and experimental results are attributed to mechanical limitations in the drive train.