Streamlined body is a type of body shape in which the middle portion of the body is broad and there are two tapering ends. Fishes have a streamlined body shape. This shape allows them to easily move in water.
When a fish swims in water, the muscles that cover its skeleton cause the front part of the body to curve towards one side. On the other hand, the tail (having fins) curves towards the opposite side.
Then, immediately the body and the tail curve towards the other side. This causes a jerk, thereby pushing the body to move forward. Many such jerks in succession help the fish move forward.
Function of fins: