Clownfish use counting abilities to identify fellow fish

A study suggests that clownfish, known for their distinctive white stripes, may possess the ability to use rudimentary counting to recognise fellow fish. The study, published in the Journal of Experimental Biology, found that clownfish can count up to three stripes on other fish and use this skill to identify potential threats to their homes and social order.

Counting skills in the animal kingdom are known to have various benefits, such as helping animals find safety in group sizes or grab bigger meals. In the case of clownfish, their ability to count stripes may serve the purpose of identifying members of their own species and distinguishing them from potential intruders.

To investigate the counting abilities of clownfish, researchers conducted experiments using young, lab-raised common clownfish (Amphiprion ocellaris). The fish were placed in individual aquariums and introduced to other clownfish with different stripe patterns, all protected inside transparent boxes. The study found that the resident clownfish reacted more aggressively towards intruders with the same number of stripes as themselves. In another experiment, groups of clownfish were exposed to resin decoys with different stripe patterns, and the fish showed a clear preference for attacking the decoys with three stripes.

The study’s lead researcher, Kina Hayashi, a marine ecologist at the Okinawa Institute of Science and Technology, has long been interested in the role of stripes in clownfish behavior. Previous research has shown that clownfish pay close attention to stripe patterns and react more aggressively to decoys with matching stripes Hayashi’s study builds on this knowledge by suggesting that clownfish can actually count the stripes and use this information to identify potential threats.

While the study provides evidence for the counting abilities of clownfish, some experts remain skeptical and question whether the fish are truly counting or simply noticing the white colouration on the intruders.