Aquatic species have evolved highly efficient modes of swimming through natural selection. The most efficient in terms of forward thrust are Thunniform-mode swimming species (eg. tuna, shark). These species are propelled by lateral oscillation of a stiff lunate caudal fin with motion primarily limited to the fin and peduncle (aft tail) regions. In this paper we describe the application of biomimicry to the use of swimming hydromechanics in the development of a new tidal current energy conversion device. The development process is briefly described and some preliminary simulation results, based on computational fluid dynamics, are presented. Results indicate that potential exists for the development of low-cost efficient devices based on the biomimetic concept.