Some animals are poorly named. The flying lemur doesn’t fly and isn’t a lemur. The mantis shrimp isn’t a mantis or a shrimp. The killdeer couldn’t. But the giant bumphead parrotfish… it’s a giant fish with a beak like a parrot and a bump on its head. Nice one, biologists. You can have a point for that.
The giant bumphead parrotfish (Bolbometopon muricatum) is the biggest herbivorous fish in coral reefs. It can reach 1.5 metres in length and weigh over 75 kilograms, and it has a distinctively bulbous forehead. Why? There are rumours that it uses its head to ram corals, breaking them up into smaller and easier-to-eat chunks.
But Roldan Munoz from the National Oceanic and Atmospheric Administration has discovered one definite use for the bump: headbutting rivals. Check out the video below – it all kicks off at the ten-second mark, and I love the “Whoooah” that follows.
While watching the parrotfish at Wake Atoll, in the middle of the Pacific, Munoz’s team heard “loud jarring sounds”. They soon found that the males were smashing their heads together head-on, and then trying to bite each other in the flanks.
To the team’s knowledge, this behaviour has only ever been described once: on a dive blog, describing a sighting in the Red Sea. Bear in mind that this is one of the largest reef fishes, and swims in large groups. As Munoz asks, “How could this dramatic aspect of its social and reproductive behavior have gone unnoticed?”
There are two possible reasons. First, the parrotfish has been severely overfished. It swims in large groups making it easy to net by day, and sleeps in shallow water making it easy to spear by night. It also grows slowly and takes years to reproduce, so even a moderate amount of fishing seriously hurts the population. Second, and related to the first reason, the fish is now very wary of humans and tends to swim away if approached.
Wake Atoll is an exception. It’s a US Marine National Monument, and the fish are protected from nets and spears. There are plenty of them, and they’ve never learned to fear divers. As such, their dramatic contests could finally be filmed. Just think about how many cool behaviours we have yet to see because we have either exterminated or terrified the animals that perform them.
Reference: Munoz, Zgliczynski, Laughlin & Teer. 2012. Extraordinary Aggressive Behavior from the Giant Coral Reef Fish, Bolbometopon muricatum, in a Remote Marine Reserve. PLoS ONE http://dx.doi.org/10.1371/journal.pone.0038120