Purpose of rainbow shimmer is unknown
From the darkness of a fish tank comes a blur of movement, followed by shimmering rainbow light.
That’s what it looks like when ghost catfish go for a swim.
The species appear transparent, or clear, at first, but as they move, the fish begin to glow with a rainbow light.
A new study found why: Ghost catfish reflect light from within.
That’s different from other animals that change colours as they move.
Those animals reflect light off outer surfaces like feathers and scales.
What is a ghost catfish?
Ghost catfish are a species of fish with no scales.
They measure just a few centimetres in length. That’s a bit smaller than a paperclip.
Their exposed skin is so transparent that about 90 per cent of light can pass through.
Ghost catfish are sometimes called glass catfish because of their transparent skin. (Image credit: Qibin Zhao/The Associated Press)
Though they’re native to Thailand’s rivers, ghost catfish are sold in pet stores all over the world.
How do they make rainbows?
The muscles inside ghost catfish are able to bend light.
This produces a shimmering rainbow as the fish swim.
Their muscles move as they swim, resulting in flashes of colours that look like a shimmering rainbow.
This process was discovered in a study led by physicist Qibin Zhao at the Shanghai Jiao Tong University in China.
The study was published in the Proceedings of the National Academy of Science journal on March 13.
Light passes through a ghost catfish in a fish tank, revealing a rainbow of colour. (Image credit: Xiujun Fan, Qibin Zhao/The Associated Press)
Why is this unique?
There are many iridescent animals that make a shimmer, such as beetles, hummingbirds, butterflies and other types of fish.
These species mostly reflect light off external skin, scales or feathers.
Ghost catfish are also iridescent, but they are different because they reflect light from inside their bodies.
In other animals, iridescence is often used to communicate warnings, according to biologist Ron Rutowski at Arizona State University.
But scientists still don’t know what purpose ghost catfishes’ rainbows serve.
Click play to see the ghost fish glow!
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With files from The Associated Press
TOP IMAGE CREDIT: Qibin Zhao/Associated Press with graphic design by Philip Street/CBC
