Why do remora fish hitch rides on sharks and turtles?

Remoras hitch rides by using an oval suction disc on the top of their heads, which is a modified dorsal fin. By attaching to sharks, turtles, rays, or even boats, they can travel long distances without swimming constantly. The arrangement can benefit remoras because they gain transport and food leftovers, while the host may be only mildly bothered or sometimes cleaned of parasites. The relationship is often described as commensalism, though the exact balance can vary by species and situation. Their unusual head structure is one of the most specialized adaptations in the fish world.