Clownfish have learnt to count their stripes – but only to annoy their brethren

It has been experimentally proven that clownfish can count or otherwise determine the exact number of stripes. Scientists made many realistic mock-ups with different colours, and there was always a clear pattern between the number of stripes on the mock-ups and the reaction of the fish to them. The most aggressive clownfish are those that look most like themselves – the most likely competitors for housing inside the actinia.