Intelligence, coordination and slipperiness. Also, to rephrase your question correctly, "How do fish in schools swim without colliding with one another."
to swim
Thats how they swim
they swim
Yes, all whales are fishes because they swim like fishes.
separate vertebrate
they swim not run
Yes they can swim.
salmon
Yes. Fins, a swim bladder, the composition of their bones, and their muscles all help a fish to swim.
they die
Nope. Piranhas are freshwater fishes.
Increases the fish's volume by filling the swim bladder with oxygen.