Clownfish Catfight

May 8, 2013

What happens when a pair of female anemonefish meet?

While diving at Pulau Hantu over the Labour Day holiday, I noticed a plume of sediment emanating from an area along the reef crest so I swam by to investigate.

As is evident from the video, the water was quite turbid, so it took awhile for my eyes to focus on what was going on, but I soon realised that I was witnessing something I’d never seen before – a pair of similar-sized anemonefish in a scuttle outside the anemone!

It’s not apparent what they are scuttling about, but since they are both of almost equal size, I suspect that the two of them are females. Usually, within an anemone that is occupied by anemonefish, one anemonefish is distinctly larger than the rest. Anemonefish are hermaphrodites, this means that they can change their sex. All anemonefish are born male, and when the time becomes appropriate, they change into females. This change is irreversible. The females are usually the largest of all the anemonefish that occupy that particular anemone. In some species there could be several individuals that are similar-sized.

Incidentally I took a photograph of this same anemone previously and there were just two anemonefish then. As is clear, one is distinctly larger than the other.

Though I was not around to witness the commencement of this scuttle, surmise to say one of the two large anemonefish came from somewhere else; perhaps it was displaced when something unforeseen happened to its original anemone or it got lost for some reason (occasionally anemonefish do wander away from their anemone).

It has been observed in aquariums, that when a new female anemonefish is introduced to an anemone with an existing female anemonefish, the resident female will challenge the newcomer. Because aquarium environments tend to be small, this leaves little room for the new female to flee, so what has been observed is that the resident female backs the newcomer into a corner and keeps her there.

Unfortunately, in an anemone, there is only room for one female of that particular species of anemonefish, so one will have to leave. I didn’t stay till the end of the fight, though I did observe them for 12 minutes (the video is only slightly over a minute), so I can’t tell you what happened in the end. But it did make me realise how challenging it would be for anemonefish who have lost their anemones to find a new home, especially the females. It may seem like there is a lot of reef to go around, and plenty of ocean and coral for a fish to find a home, but in the case of anemonefish, where they have a very specific place that they find shelter in, this might not be so simple.

Anemones, like corals, are animals. They feed on plankton and some of the large ones can even trap and swallow small fishes whole. Anemones can live for many years, some species have been recorded to be centuries old. Like giant trees in the forest, once they are removed, they may be hard to replace. Unfortunately, these beautiful creatures are popular in the live aquarium trade and many are harvested from the wild for this trade.

Thanks to the movie Finding Nemo, anemonefish are associated with the tropical reefs of Australia, so it might surprise many that they can be found in urban Singapore! In fact, five species of anemonefish have been recorded in Singapore. So if you’re looking for Nemo, come diving with us in Singapore!

Posted in Biology, Videos, Wildlife Trade