I think that I have the solution. Genetically alter trout so that they will naturally have hinges. LOL.

Great thoughts, Rob. The laughing bass is an interesting starting point. At some craft fair (Santa Barbara wharf area on Sundays I think), if I recall correctly I saw decorative fish that move their tails without hinges. I do not recall if power was battery, solar, or maybe each kind was available at different stalls. I think some were koi colored for ponds. I wonder if a robotic bluegill would turn in a relatively wide circle simply by putting a barely perceptible bend in it?

Bob