Clownfish Set Social Status With Sound
November 9, 2012

Clownfish Group Status Established By Ability To Communicate

Alan McStracick for — Your Universe Online

Everything I ever needed to know about clownfish, I learned from ℠Finding Nemo´. Stop the presses. The clownfish, or anemonefish, (so called for their symbiotic mutualisms with sea anenomes), are, thanks to ℠Finding Nemo´, one of the most recognizable and least understood fish in the sea.

So, let´s begin our education of this fun colored creature. The clownfish is native to the warmer waters of the Pacific and Indian oceans. Typically they are found at the bottom of shallower seas in sheltered reefs or shallow lagoons.

With a diet that is omnivorous, clownfish will often feed on small invertebrates that would otherwise harm the sea anemone. Their fecal matter, in turn, provides much needed nutrients to the anemone.

Another example of the symbiotic mutualism of the pair is that the clownfish, it is believed, will lure small fish, using its bright coloring, to the anemone. The activity of the clown fish around its host also provides greater water circulation which is beneficial to the anemone.

The clownfish has a mucus coating that scientists believe may be sugar, rather than protein, based. This may explain why anemones fail to see them as a potential food source and do not fire off their nematocysts, or sting organelles. Scientific testing has been done that has shown that a clownfish, devoid of an outer mucus covering, was not able to survive interaction with an anemone.

Size matters when you are a clownfish. They have been seen to grow as big as approximately 7 inches and as small as just shy of 4 inches in length.

It would seem that this was pretty much everything we could learn about this fabled fish. That is, until this week, when scientists from the University of Liege in Belgium found they could interpret the speech of the clownfish.

Clownfish, it was found, produce sounds that are meant to establish and defend their breeding status within their social groups. These sounds are not, however, intended or necessary for attracting mates. This is because within a group of clownfish, there is a strict dominance hierarchy. At the top of this group, you will find the largest and most dominant female. Breeding is only done by two clownfish in the group. The male and the female will reproduce through external fertilization.

The new study, published this week in the open access journal PLOS ONE by Orphal Colleye and colleagues, explains how the top male and female keep their positions in the hierarchy.

Clownfish are what is known as sequential hermaphrodites. What this means is that they first develop as males. As they mature, they become females. If the top female of the group is removed, say by death, then one of the larger and more dominant males will become a female. All the remaining males move up the ladder of the hierarchy one wrung.

The study focused on the importance of sounds made by the fish contained in this social structure. What they found was that the clownfish makes two distinct main sounds. The first is the aggressive calls made by charging and chasing fish. The second were sounds that were made by the more submissive fish. These smaller fish would typically make sounds that were shorter, higher frequency pulses than the sounds emitted by the larger fish.

Colleye and colleagues say that these acoustic signals are especially significant for clownfish as their entire social structure is formulated around a size-based hierarchy.