An experiment shows that clownfish can count the stripes of other fish to identify them as intruders
Nemo, the little animated fish, is an icon, curled up with his father in an anemone. Pixar would like us to believe that anemonefish’s lives are mostly peaceful and quiet. But the myth belies reality.
Anemonefish (also called clownfish) are feisty little creatures that zealously defend their anemone house from intruders. And although they may sometimes share space with anemonefish of other species, intruders from the same species are not welcome.
How do clownfish distinguish their fellow stripers from other striped fish? According to Kina Hayashi of the Okinawa Institute of Science and Technology in Japan, clownfish species that live in the same locations typically display a wide range of stripe patterns, from three vertical white bars to none.
Could clownfish count the number of white bands on other fish’s bodies to distinguish between friends and foes? Kina Hayashi and her colleagues publish the surprising discovery in the Journal of Experimental Biology that the common clownfish (Amphiprion ocellaris) You can count.
Nemo knows how to count the stripes of other fish
To find out, Hayashi, Noah Locke and Vincent Laudet raised a school of young Nemo, common clownfish, from eggs to ensure the fish never saw other anemonefish species. When the hatchlings were about six months old, Hayashi filmed their reactions to other species of anemonefish, such as the Clarke anemonefish (A. clarkii), the orange skunk clownfish (A. sandaracinos) and the saddle clownfish (A. polymnus) as well as invaders of their own species to find out how they reacted.
As expected, the three white banded clownfish had the hardest time against members of their own species, taking on 80% of the fish for three seconds and even holding a standoff for 11 seconds with some fish. .
Intruders from other species, however, had an easier time: the orange skunk clownfish – with no side bars and a white line on the back – was the worst off and could hardly be encountered, while the Clarke clownfish and the saddleback clownfish – with two and two respectively. three white bars – were slightly intimidated. “Common clownfish attacked their own species more often,” says Hayashi. But how do clownfish distinguish between members of their own species and those of others?
This time, the team isolated small schools (three fish) of juvenile clownfish in individual aquariums and filmed the fish’s reactions to a plain orange fish model or models painted with one, two, or three white stripes, tracking the frequency with which the fish appeared The fish bit the intruder and chased him.
In fact, the young clownfish paid little attention to the smooth orange model, much like they had paid no interest to the orange skunk clownfish while biting the model from time to time and chasing it with a single rod. However, they have significantly increased the pressure on the three-stripe models; They didn’t like sharing space with strangers from three bars who looked like them. Two-striped fish were also harassed.
Hayashi suspects that clownfish’s aversion to two-barred fish may be related to their evolution. The common clownfish first develops two white stripes at 11 days of age before developing the third three days later. He suspects that clownfish that grew up with other two-striped offspring might see fish with two white bars as competitors that need to be driven away.
For example, young clownfish living in anemones can distinguish species that pose a threat from those that do not by the number of white stripes on their sides. This allows them to defend their habitat from invaders who might try to drive them away, while paying less attention to fish of other species that have little interest in taking up residence in their anemone abode.
REFERENCE
Counting Nemo: Anemonefish Amphiprion ocellaris identifies species by the number of white bars