Remoras, also called suckerfish or whalesuckers, are known for hitchhiking on the back of large deep sea creatures like whales and sharks. They attach themselves to large fish via a powerful suction disk which sits on their heads like a flat, sticky hat.
But these fish don't just enjoy their free ride; the two share a mutually beneficial relationship. The host gets the parasites on their body removed while the tiny riders get their meal, protection from predators and also have chances of meeting mates.
Suckerfish were found to position themselves smartly near 3 places where they would experience least amount of resistance from the flow of water: behind the blowhole, behind and next to the dorsal fin, and behind the pectoral fin. These areas tend to experience 84% less drag, which makes it easy for them to stay attached.
Although the remoras’ suction disks are so strong that they could stick even at the tail (where the drag is maximum), in order to conserve energy they surf inside a thin layer of liquid called boundary layer on the surface of their floating islands aka the hosts. Here the drag force is lesser by 72% which allows them to move easily without detaching themselves entirely from their host even when the host moves at upto 7 times their speed.
Image and Video Credits: Stanford University & Cascadia Research Collective