Nemo And Fellow Clownfish Show Impressive Ability To Count Stripes, Study Finds

Nemo and his fellow clever clownfish can count to determine whether other fish are friends or foes, a new study has revealed.

Researchers say the feisty, territorial fish tell between threatening intruders and innocuous cohabitants by counting the stripes across their bodies.

Scientists tested the orange fish to gauge their reaction to fish of the same or similar species with one to three characteristic white stripes.

Keeping a tally, the researchers found the clownfish counted the stripes of other fish and took a dislike to those with three stripes like themselves, as well as fish with two stripes.

But those with one or no stripes they tended to leave alone.

The Japanese scientists behind the study, published in the Journal of Experimental Biology, assert that this is proof of the fish’s impressive ability to count.

Though Pixar would have you believe that Nemo and his fellow cohort of clownfish are timid, welcoming fish, the truth is far from that.

Anemonefish – more commonly known as clownfish – are actually feisty little creatures who enthusiastically defend their anemone homes from intruders.

And whilst it is sometimes OK for the fish to share their habitats with anemonefish of other species, it is rarely if ever acceptable to cohabit with intruders of their own species, who receive particularly frosty receptions.

According to the researchers, anemonefish species that live in the same locations tend to have a wide range of stripy patterns – from three vertical white bars to none.

Previous studies have shown that coral reef fish including clownfish develop their stripes so other fish can find them in a crowd.

But researchers from the Okinawa Institute of Science and Technology set out to decipher how anemonefish tell members of their own species apart from other similarly stripy fish.

Dr. Kina Hayashi and his colleagues raised a school of young Nemos – or common clownfish – from eggs, to ensure that the fish had never set eyes on other species of anemonefish.

Once the youngsters reached six months, Dr. Hayashi began filming their reactions to other anemonefish species – including Clarke’s anemonefish (A. clarkii), orange skunk clownfish (A. sandaracinos) and saddleback clownfish (A. polymnus) – as well as intruders of their own species.

As expected, the common clownfish gave members of their own species with three white bands like them the hardest time; facing off against four-fifths (80 percent) of the fish for up to three seconds and even maintaining an 11-second standoff with one fish.

By contrast, the researchers found intruders of other species had an easier time.

The orange skunk clownfish – which has no sidebars but a white line along its back – got off the lightest and was barely confronted.

Meanwhile, Clarke’s clown fish and saddleback clownfish – which boast two and three white bars, respectively – were mildly bullied.

“Common clownfish attacked their own species most frequently,” Dr. Hayashi observed.

But it remained a mystery to the scientists as to how the clownfish distinguished between members of their own species and others.

In another set of tests, the researchers isolated small shoals of three young common clownfish in individual tanks and filmed their reactions to either a plain orange fish model or models painted with one, two or three white bands – keeping a tally of how often the fish bit and attempted to chase off the offending intruder.

They found the young clownfish paid little attention to the plain orange model – similar to the lack of interest they had shown in the orange skunk clownfish – and merely occasionally nipped and pursued the model with a single bar.

However, they again upped the ante on the three-striped models, demonstrating how little they liked sharing space with the three-barred strangers who looked like themselves, whilst the two-striped model also received a rather unwelcome reception.

Dr. Hayashi suggested that the clownfish’s aversion to fish with two bars could relate to their development.

Common clownfish initially form two white stripes at around 11 days old, before gaining the third three days later.

Therefore, Dr. Hayashi suspects clownfish who grow up with other two-striped youngsters could see fish with two white bars as competitors to be chased away.

Therefore, the researchers’ study shows young common clownfish that make their homes in anemones can distinguish between species that pose a threat and those that do not based on the number of white bars on the fish’s sides.

This allows them to defend their abode from intruders that might try to evict them, whilst paying less attention to fish of other species that have little interest in setting up home in their anemone residence.

Produced in association with SWNS Talker