Abstract: The outstanding characteristics of body and/or caudal fin(BCF) fish, such as the fast speed and high efficiency, have currently attracted the interests of the bionic researches, and some robotic fish have also been constructed. However, there is a huge gap between the biological fish and the fish robot in the swimming performances, which have further propelled the mechanism study of fish locomotion. In particular, research status at home and abroad field are systematically summarized through the mechanical properties and the hydrodynamic properties. Accordingly, the key techniques in BCF robotic fish, the variable impedance actuation and the eddy current control are discussed in detail. And the developing tendencies of the related research in compliant robot fish are also presented. Overall, the theories of bionic inter-disciplines will be further developed along with deep research of this subject, and the broad prospects of practical application can be expected with the decreasing gaps between the robotic fish and their nature samples.

Key words: body and/or caudal fin fish, hydrodynamic properties, locomotion mechanism, variable impedance property