Remora, Hitch-hiker Fish.
The remoras, sometimes called suckerfish, are a family (Echeneidae) of ray-finned fish in the order Perciformes. They grow to 7–75 cm (0.23–2.46 ft) long, and their distinctive first dorsal fins take the form of a modified oval, sucker-like organ with slat-like structures that open and close to create suction and take a firm hold against the skin of larger marine animals.[3] By sliding backward, the remora can increase the suction, or it can release itself by swimming forward. Remoras sometimes attach to small boats. They swim well on their own, with a sinuous, or curved, motion.
Some remoras, such as this Echeneis naucrates, may attach themselves to scuba divers.