The body shape and caudal fin shape are a huge indicator of how fast a species of fish is (caudal fin being the back fin or "tail"). Fish that have more rounded bodies, like sunfish, will be much slower, whereas fish with streamlined "torpedo" shaped bodies, like tuna, will move faster. A rounded caudal fin will also move slower, while a more crescent moon shape will move fastest. These body shapes reduce the amount of drag that may be produced when moving through the water. The body shape and caudal fin shape are a huge indicator of how fast a species of fish is (caudal fin being the back fin or "tail"). Fish that have more rounded bodies, like sunfish, will be much slower, whereas fish with streamlined "torpedo" shaped bodies, like tuna, will move faster. A rounded caudal fin will also move slower, while a more crescent moon shape will move fastest. These body shapes reduce the amount of drag that may be produced when moving through the water.