What features of the external structure allowed the fish to adapt to life in the water?

The main adaptive feature is the streamlined shape of the body, because with its help, less resistance is created when moving. It is also facilitated by covering the body with scales and mucus. The tail, pectoral and pelvic fins provide maneuverability. Thanks to the lateral line, which perceives the movement and vibration of the surrounding water, the fish are well oriented in space and track their prey. The absence of external hearing organs is associated with good sound propagation in the aquatic environment.