A wide range of fish and marine mammals can be fabricated using one or more "torque reaction engines". TREs are self-contained units that can be embedded within a flexible body. The body, swimming mode (fish, marine mammal, medial paired fin, jellyfish, flagellum), are variables that can be changed to suit a service to be performed.
Multiple TRE can be arranged in a row, like this:
Sea lions, salmon, eels, jellyfish, flagellum, tuna, and other creatures of the sea can all be modelled as Phish. Phish should be capable of speed and power-output similar to that of their real counterparts.
TRE can be relocated along their driveshaft, which will allow the Phish to roll between fish and marine mammal orientations.
The trout image at the top is by Eric Engbretson for U.S. Fish and Wildlife Service - http://images.fws.gov