Giant headbutting fish

The world’s biggest parrotfish – the bumphead parrotfish Bolbomepoton muricatum – have been caught on camera for the first time headbutting each other.

[vimeo]http://vimeo.com/43626409#[/vimeo]

The finding was published in the open access PlosOne (so go have a read) and as Roldan Muñoz and his colleagues point out, the only way they got to observe this crazy behaviour was in a highly protected, remote part of the oceans (Wake Island in the Pacific).

As they say:

While observing large aggregations of Bolbometopon in ~7 m of water, we heard loud jarring sounds and confirmed they arose from violent impacts between males engaged in repeated, ritualized headbutting behavior

And surely the question we’re all thinking is…

How could this dramatic aspect of its social and reproductive behavior have gone unnoticed?

The authors have two ideas about that:

1) Low population densities resulting from overfishing dampen competition for resources (females or spawning territories) and/or disrupt the social system so that headbutting contests are uncommon and no longer advantageous.

2) Headbutting contests are common, but negative responses to humans in exploited populations preclude observations of natural behavior.

Happy World Oceans Day everybody. Horray for huge fish and ritual headbutting!