Headbutting fish

In the wild, male animals use headbutting to defend their territory, among other things. We have always thought of land animals, like bison and rams, as the ones that headbutt.  Now we know that fish do it, too.  Specifically, the giant bumphead parrotfish.

The bumphead parrotfish was named for the giant bump on the front of its head.  Turns out they also actually bump heads under water. You can see them doing it here:

Bumphead parrotfish headbutting

It’s hard to tell from the pictures, but these are huge fish.  They can grow four to five feet long and weigh 100 pounds, making some of them as big as a 13-year old.  They are also a potentially endangered species (PDF).  Their lifestyle makes them easy targets for overfishing: they hang out in groups in shallow water, where spearfishers get them.  The fish have learned, though, and are now skittish of humans.  It’s hard to know what they do when no one’s watching:  there aren’t many of them around, and when do we find them, they quickly swim away.

There are a few marine areas where bumphead parrotfish are protected.  In these areas the fish still thrive, and they don’t know to be afraid of people.  It was in one of these areas that scientists first heard, and then saw, the fish headbutting.

People thought that the fish use their heads to bump into the reef and break off chunks to eat.  However, the bony plates on female heads are not as big as the ones on males, and the females have no trouble eating (you can see a picture of the male/female difference in the original paper).  Now we may know what those plates are really used for:  a mating ritual, and territorial defense.

Headbutting aside, the bumphead parrotfish are thought to be gentle giants.  Their diet mainly consists of coral reef. In fact, they are the biggest plant-eating fish on coral reefs. Being so big, they can eat a lot: up to five tons of reef each year, per fish.  No other fish eats that much reef, and without the bumphead parrotfish, the reef would just keep growing.

The scientists observed the fish in the video at Great Barrier Reef off the coast of Australia, where are still plenty of bumphead parrotfish.  The fish eat the reef as fast as it grows. Without them chomping away on it, the whole reef would change, and probably for the worse: the reef would get too big and become unstable.  Also, different species would move in.  This would disrupt the ecology of the entire reef system.

The scientists’ discovery was a surprise benefit of bumphead parrotfish protection.  Not only is the reef healthier, and the fish are surviving, but we’ve also learned something totally unexpected about fish. And that’s what science is all about!

Note:  This is my the first “Family Day at The Beach” post.  Try sharing it with kids.  I’d love to hear what you think.

Image credit:  http://underwater.com.au/image/id/9476/

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One thought on “Headbutting fish

  1. Head bumping is a way of showing dominance. “I’ve got a better head than you — nyah, nyah, nyah!” Since it’s hard to watch the bumphead parrotfish, you might want to try an aquarium with some “kissing” gouramis (Helostoma temminckii). While they can get big, I keep 3 medium size (4″ long) in a 20 gallon long tank and they often show their dominance by, you guessed it, “kissing”. They form their mouths into a kissing position and then push against another gourami’s mouth. They can keep up at this for 5 to 10 minutes, quite like young teenagers.

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