How do fish and jellyfish swim?

Fish move by flapping their fins or through wriggling movements of their body. In addition , they have an air bladder, which they can fill with gases when needed , These features make them lighter and they can float in the water like a submarine, Jellyfish usually drift. To move forward,they pull together their their cap and push the water downwards- a same recoil principle that is used in jet fighters and octopuses.
Most of the jellyfish have long arms, which they use for catching their prey or for defence.