Swimming is far common among animals than is flying.
There are many swimming modes among aquatic creatures. A mode is most often named after an exemplar of that mode. Wave move backward both with respect to the fish's body and with respect to the free stream. The mode is also used by some largely or entirely limbless amphibians, by aquatic snakes, and by the smooth-bodied polychaete worms. This mode is used by the perches, trout, cichlids, mullets, and so forth.