What are adaptations in fishes due to which they are aquatic?
(i) The body is boat shaped or stream lined.
(ii) Head, body and tail are compressed to make it suitable for locomotion in water, so that it offers little or no resistance for swimming in water.
(iii) The pelvic fins, pectoral fins, dorsal fin, anal and caudal fins act as paddles and control the direction of movement in water and provide balance.
(iv) The gills are well developed and suited for gaseous exchange in water.
(v) The lateral line receptors enable the fish to detect any changes caused by mechanical disturbances in the surrounding water. (vi) The presence of air bladders in many bony fishes acts as an accessory respiratory organs as well as an organ for buoyancy. Using these bladders the fishes are able to maintain themselves at desired depths.
(vii) The body is covered with scales.
(viii) The presence of a third membrane called the nictitating membrane in the eye.