Our company, Admiral Fluidics, a division of Horrigan Labs Corp. is developing a caudal cycle propulsion system that is many times as efficient as a fish or marine mammal caudal fin. No cavitation, no deflection losses, non-fouling, high bollard pull, high speed, etc. Darwin didn't forsee us getting in on the evolutionary act. Fish will be so jealous. It won invention of the year this year at San Diego Inventors Forum and an Autodesk Cleantech Award worth $80+ grand as well. We are developing it for commercial ship propulsion. Fuel & carbon emission savings are amazing.
External link: http://admiralfluidics.com/Commercial%20Propulsion.htm