To the ancient Romans, Marc Antony was an invincible leader who no mortal could defeat. When his navy was beaten in the Battle of Actium his citizens had to invent a non-human explanation for his loss. They found the perfect foil in a strange fish that sticks to other animals, or boats, and hitches a ride.
This fish is called the Remora, or Sharksucker, and although most of you have probably not seen one in person, many will recognize it as the strange little fish that attaches itself to sharks, whales or sea turtles in those PBS or Discovery Channel nature programs.
Remoras are found in tropical seas throughout the world. They have a large suction cup, called a “sucking plate”, on top of their heads. They use this amazing structure to attach to other animals.
The sucking plate is actually a greatly modified first dorsal fin. The dorsal fin is found on top of a fish’s body (it is the fin that breaks the surface on sharks, like in the movie “Jaws”.) Most fish have two, conveniently named the first and second dorsal fins. The remora’s first dorsal has become flattened into a disk with about twenty ridges on it. Each ridge can move independently (think of a Venetian blind). When it touches a fish the ridges are lifted up to create a vacuum, sealing the plate to whatever it attaches to.
Occasionally the remora will attach to a migrating animal such as a sea turtle or swordfish. If the host swims northward the remora is carried with it. In this way they are sometimes brought to the shores of New England.
Generally a young remora will find a shark and stay with it throughout its life, mating only with other remoras sharing the same host. If the host dies the remoras as a group will search for a new one. The shark-remora relationship is a form of symbiosis known as commensalism; where one partner (the remora) benefits and the other (the host) is unaffected.
The remora does not harm its host as parasites do. It attaches for three reasons: The first is for transportation. Living in the open ocean requires an animal to expend a lot of energy swimming. By hitching a ride it conserves this energy letting the bigger fish do all the work. One species using another for transportation is a special form of commensalism known as phoresy. The second is protection. Who would attack a fish that is attached to a ten-foot long shark? The third reason is food. Sharks are messy eaters. When the shark catches a meal the remora simply releases its grip, eats the scraps, and then reattaches. Some remoras have even been found inside the mouths of large sharks (they enter through the gill slits to avoid the teeth) robbing food that the shark tries to swallow. Although I’m not sure how common this is, remoras are also known to be copraphagic, meaning it feeds on its host’s feces. Yuk.
The remora is usually black and white striped with a dark back and white belly. This is consistent with the countershading coloring of most fish (dark on top to blend in with the ocean bottom, light on the bottom to blend in with the sunlit surface). But remoras can exhibit color reversal. When a remora attaches to a bottom fish, like rays or nurse sharks, it flips itself over onto the host’s back so not to be crushed. Soon after flipping over, the belly (which is now on top) turns dark. By being able to achieve color reversal the remora does not lose its ability to countershade, even when upside down.
Upside down remoras on a resting nurse shark.
One interesting feature of the sucking plate is that the faster the host swims the tighter the grip becomes. This is vital to the fish because it will not become dislodged by a fast moving host. To remove a remora you have to push it forward; pulling back simply tightens its grip. Although this fact is important for the sharksucker, it was also once used by the Arawak Indians of Cuba (a practice first described by Christopher Columbus, who of course eventually annihilated the tribe), as well as by some Australian aborigines. These people used remoras as living fish hooks. When a large shark or sea turtle was sighted off a beach they would release their remora, with a line attached to the tail. The remora would stick to the shark and the natives would simply haul both animals into shore. While the Arawaks took good care of their remoras, keeping them alive in saltwater pens, the Australians ate theirs with the prey.
Incidentally, to give you an idea of the strength of the sucking plate, when pulled backwards by the fishermen the plate will actually tear out of the fish’s head before letting go of the host.
Getting back to the Romans, legend says remoras attached to Antony’s boat and slowed it down so much it was overtaken by the enemy. This clearly could not have happened since hundreds of fish would be needed. Still, it led to the fish’s name. The word “remora” is Latin for “holding back”. The myth surrounding remoras was strong even for the ancient Greeks, for the scientific name of this fish is Echeneis, which comes from combining the Greek words meaning “to hold back” and “ship”.
Fun Fact: Fossil remoras had a fully formed sucking plate as early as 50 million years ago.