The Great Barrier Reef anemonefish (Amphiprion akindynos) can see ultraviolet light and may use it as a ‘secret channel’ to find both friends and food, according to new research.

Anemonefish, also known as clownfish, are fishes from the subfamily Amphiprioninae in the family Pomacentridae.

They are easily recognized by their striking orange and white patterning, and live in close symbiosis with tropical sea anemones.

“Due to their striking appearance and lifestyle, we were interested to know how their visual system might be adapted to their visual ecology and behaviors,” said Dr. Fabio Cortesi, a researcher in the Queensland Brain Institute at the University of Queensland.

Dr. Cortesi and his colleagues focused their study on Amphiprion akindynos, a species mainly found on the Great Barrier Reef in Australia.

“We looked at everything starting with the genes Amphiprion akindynos uses to see and what proteins it expresses, and in combination with anatomical data, predicted what it can see,” he said.

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

The team was able to discover a unique specialization in the eye of the fish that may allow them to better detect friends and their anemone.

“In the part of the anemonefish’s eye that looks forward, the photoreceptors detect a combination of violet light and ultraviolet (UV) light,” said Dr. Fanny de Busserolles, also from the Queensland Brain Institute at the University of Queensland.

“They seem to be very good at distinguishing color, and very good at seeing UV — it looks like they use it a lot.”

“The special ability made sense, based on the fish’s environment and food source,” said Dr. Sara Stieb, from the Queensland Brain Institute at the University of Queensland, the University of Bern and the EAWAG Swiss Federal Institute of Aquatic Science and Technology.

“Anemonefish live very close to the surface, where UV light can easily penetrate. 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.”

UV vision lent anemonefish another important advantage.

“Their visual system seems to be very tuned to recognizing who is their friend and who is not,” Dr. Cortesi said.

“The white stripes on anemonefish reflect UV, which means they should be easier for other anemonefish to recognize.”

“By contrast, a lot of the bigger fish — including ones that eat anemonefish — cannot see UV, so if you want to communicate on the reef over short distances, then UV is a very good way to do this.”

“UV is essentially a secret channel that only these little fish can use to talk to each other.”

“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 appears in the journal Scientific Reports.

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Sara M. Stieb et al. 2019. A detailed investigation of the visual system and visual ecology of the Barrier Reef anemonefish, Amphiprion akindynos. Scientific Reports 9, article number: 16459; doi: 10.1038/s41598-019-52297-0