Underwater, we can truly move through 3 dimensions, free from the constraints of gravity in the state divers called neutral buoyancy, or as its also known the best feeling in the world. Fish of course can move in this environment far more freely and dramatically than we can.
Here a school of fusilliers has fromed a torus around a potential threat. The "threat" is a parrotfish that actually feeds on coral so the fusilliers have overreacted somewhat but better safe than sorry, eh? There has been some quite interesting work done on modelling the fluid movements of fish shoals - here's an example but there's surely more out there for those interested.