The common clownfish (Amphiprion ocellaris), especially known from the Pixar film ‘Nemo’, is capable of counting, as demonstrated by Japanese scientists in the ‘Journal of Experimental Biology’.
Anemone fish (also known as clown or Nemo fish) are feisty little creatures that eagerly defend their anemone homes from intruders.
And while it is sometimes okay to share with anemone fish of other species, it is never okay to cohabit with intruders of your own species.
So how do anemone fish distinguish members of their own species from other striped fish?
According to the lead author of the study, Kina Hayashi, from the Okinawa Institute of Science and Technology (Japan), the species of anemone fish that live in the same places They tend to have a wide range of stripe patterns, from three vertical white bars to none.
In this way, he has tried to defend the thesis that the anemone fish is capable of counting the number of white bands on the body of other fish to distinguish its friends from its enemies.
Research with Nemo
To find out, the research team raised a school of young common clownfish, or Nemo, from eggs, to ensure the fish had never seen other anemone species.
Once the young were about 6 months old, Hayashi filmed their reactions to other species of anemonefish, including Clarke’s anemonefish (A.clarkii), orange skunk clownfish (A.sandaracinos), and clownfish. saddleback (A.polymnus), as well as intruders of their own species, to find out how they responded.
Indeed, the common clownfish gave members of its own three-white-banded species the toughest time, taking on 80% of the fish for up to three seconds and even holding an eleven-second standoff with one fish.
On the contrary, intruders from other species had it easier: the orange skunk clownfish, without side bars and with a white line along its back, came out lighter and barely struggled, while Clarke’s clownfish and The saddleback clownfish, with two and three white bars, respectively, were slightly intimidated.
“The common clownfish attacked its own species more often,” reflects Hayashi.
Clown fish and their logic with stripes
But how did clownfish distinguish between members of their own species and others?
This time, the team isolated small schools (three fish) of young common clownfish in individual tanks and then filmed the fish’s reactions to an orange fish model or models painted with one, two or three white bands, keeping a count of the frequency with which the fish bit and chased the offending intruder.
Sure enough, the young clownfish paid little attention to the smooth orange model, similar to the lack of interest they had shown in the orange skunk clownfish, as they nibbled and chased the model with a single rod from time to time.
However, they really increased the pressure on the three-stripe models; They didn’t like sharing space with three-bar strangers who looked like them.
And the two-striped models also suffered harassment.
Hayashi suggests that clownfish’s aversion to fish with two bars could be related to their development.
The common clownfish initially forms two white stripes at eleven days of age before gaining the third three days later.
He suspects that clownfish growing up with other two-striped juveniles might see fish with two white bars as competitors to chase away.
Therefore, young common clownfish living in anemones can distinguish species that are a threat from those that are not based on the number of white bars on the sides of the fish.
This allows them to defend their abode from intruders who might try to evict them, while paying less attention to fish of other species that have little interest in taking up residence in their anemone residence.
