Nemo’s cousins have a way of finding him

Clownfish, made famous by the movie Finding Nemo, may have their own secret way of finding friends and anenomes.

They can see ultraviolet (UV) light and are good at discerning different colours, according to scientists at the University of Queensland, Australia, and the University of Maryland in the US.

The unique adaptation could give them several advantages for finding food and seeing their own kind as well as predators.

Many clownfish species are bright orange, with striking white stripes framed by black, and live symbiotically with sea anemones – colourful polyps that trap and eat other unsuspecting fish.

It’s well known that most fish use vision for foraging, survival and mating, but this could differ between species according to their light habitat and environment, and influence their behaviour.

To understand how clownfish see the world, the researchers analysed the visual systems and ecology of a specific species of anemonefish in the Great Barrier Reef, Amphiprion akindoynos, which co-author Fabio Cortesi says is effectively Nemo’s cousin.

“We looked at everything starting with the genes they use to see and what proteins they express, and in combination with anatomical data, predicted what these anemonefish can see,” Cortesi explains.

“Proteins involved in detecting light have minute, well-known differences that influence which wavelengths of light they absorb.”

The team found a novel specialisation in the eye of the fish that gives them keen visual acuity.

“In the part of the anemonefish’s eye that looks forward, the photoreceptors detect a combination of violet light and ultraviolet light,” says co-lead author Fanny de Busserolles.

This special ability makes sense when you consider the fish’s environment and food source, according to lead author Sara Stieb.

“Anemonefish live very close to the surface, where UV light can easily penetrate,” she says. “They live in symbiosis with anemones, and the anemones use UV to grow.

“Moreover, anemonefish feed on zooplankton which absorb UV light, so it would appear like dark dots against the background, making it easy to find.”

It could also help them see and recognise each other, because their white stripes reflect UV. This gives them a distinct advantage over many big fish, including their predators, which can’t see UV light, explains Cortesi.

“UV is essentially a secret channel that only these fish can use to talk to each other,” he says. “They can be as flashy as they want and they won’t be seen – and it might be how Nemo’s cousin finds its friends.”

The study is published in the journal Scientific Reports.

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