Remember the old line that Ginger Rogers was more talented than Fred Astaire because she had to do everything he did, backwards and in high heels? Well, most fish would be lousy dancers, and not just because they don't have feet. The majority of them have an anatomical design that allows them to flex their bodies and move their tail, or caudal, fin to thrust themselves through the water. An area of muscle near to the tail generates most of the force. That's a great way to swim forward in a hurry, but not so great for rear motion.
Some species, however, can mimic Ginger using different methods of locomotion. Triggerfish, members of the family Balistidae, for example, use a method called balistiform mode, in which they move by undulating their dorsal and anal fins. They have fins that are inclined so that they can thrust forward, which moves them backward through the water. The electric eel (Electrophorus electricus) is similarly nimble in both directions because it uses a form of locomotion called gymnotiform mode, which involves undulating its lengthy body and flapping its anal fins