Researchers have discovered that Great Barrier Reef anemonefish can see ultraviolet light (UV) and may use it as a ‘secret channel’ to find both food and friends.
Anemonefish, or clownfish, were made famous by the movie Finding Nemo.
While their striking orange and white patterning make them very recognisable, very little is known about how anemonefish recognise each other.
That’s because their visual systems are still a bit of a mystery.
In order to find out more about how anemonefish see the world and how this influences their behaviour, researchers at the Queensland Brain Institute (QBI), in collaboration with researchers of the University of Maryland (USA), analysed the visual systems of a particular species of anemonefish, Amphiprion akindynos, known as the Great Barrier Reef anemonefish.
“It’s basically Nemo’s cousin,” said QBI researcher Dr Fabio Cortesi.
Predicting what anemonefish can see
“We looked at everything starting with the genes they use to see, as well as what proteins they express.”
Proteins involved in detecting light have minute, well known, differences that influence which wavelengths of light they absorb, he explained.
The QBI team and their colleagues then built a computational model to analyse the genetic data, and in combination with anatomical data, predicted what these anemonefish can see.
“The real strength of our study is its multidisciplinary approach”, said QBI researcher Dr Fanny de Busserolles, who shares lead authorship with Dr Sara Stieb.
“By using a multi-facetted approach, we were able to discover a novel specialisation in the eye of these fish that may allow them to better detect friends and their anemone,” she said.
Their unique eyes can detect UV light
“This specialisation is located in a very specific part of the anemonefish’s eye, the area that looks forward. In this area, the photoreceptors detect a combination of violet light and ultraviolet light.”
Dr Stieb, who has a joint appointment at QBI and the University of Bern in Switzerland, said, “They seem to be very good at distinguishing colour, and very good at seeing UV – it looks like they use it a lot.”
Photo: Justin Marshall.
Why UV?
It makes a lot of sense when you look at their environment and their food source, said Dr Stieb, explaining that anemonefish live very close to the surface (within 15 metres), where UV light can easily penetrate.
“Down there, they live in symbiosis with anemones, and the anemones use UV to grow,” she said.
Moreover, anemonefish feed on zooplankton, which absorb UV light. Thus, for an anemonefish that can see UV, zooplankton would appear like dark dots against the background, making them easy to find.
UV vision is used to recognise fish friends
Dr Cortesi said UV vision lends anemonefish another important advantage.
“Their visual system seems to be very tuned to recognising who is their friend and who is not,” he said.
“The white stripes on anemonefish reflect UV, which means they should be easier for other anemonefish to recognise.”
A secret communication just for little fish
“By contrast, 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,” he said.
“They can be as flashy as they want and they won’t be seen.”
“It might be how Nemo’s cousin finds its friends.”
The findings have been published in the journal Scientific Reports.
