Unlike the star of Disney’s Finding Nemo, real life common clown fish are not eager to share their home with members of their own species.
Researchers say they discovered how they kick out unwelcome guests by counting the stranger’s vertical white markings.
According to previous researchthe sea anemones that house common clownfish can also be a temporary home for other species – provided they have horizontal stripes or no stripes at all.
However, common clownfish do not tend to live with fish that have vertical markings like their own, but experiments have shown that they are more aggressive towards fish models painted with such patterns.
Scientists have now found that it is not just the presence of vertical stripes, but their number that helps the common clownfish to recognize its peers.
Dr Kina Hayashi, from the Okinawa Institute of Science and Technology, first author of the research, said: “Perhaps there are other factors besides the white vertical lines that are important to distinguish the same species.
“But this experiment at least suggested that the number of white vertical lines is important for distinguishing the same species and deciding whether to attack or not.”
Writing in the Journal of Experimental Biology, researchers in Japan describe how they took young common clownfish that had never seen other species and placed a small transparent container in their tanks. The container contained either a fish of the same species – with an orange body with three vertical white stripes – or a different species of clownfish with different markings.
The results revealed that the common clownfish showed a greater number and frequency of aggressive behavior towards members of their own species than towards the orange skunk clownfish – which has only a single white horizontal stripe on its back. However, no significant differences in behavior were seen compared to other species of clownfish, all of which had one or more vertical stripes.
The team then exposed common clownfish to model fish painted orange with none, one, two or three vertical white stripes.
The scientists found that the frequency of aggressive behavior by these groups towards the model was much lower when it was painted without stripes, compared to the striped models.
However, based on the behavior of individuals, the team found the fish were more aggressive towards the model with three vertical stripes than one stripe.
Hayashi said the results are interesting as the ecological role of the white stripe pattern in clownfish – also known as anemonefish – was not previously clear.
“This result supports[s] the idea that anemonefish are able to distinguish between different numbers of white bars, and the differences in the number of white bars help anemonefish to distinguish their own species,” she said.
