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Scientists have uncovered the mystery behind how a see-through fish is able to turn rainbow-coloured!

The ghost catfish - also known as the glass catfish - is nearly completely translucent, however when light hits it, it creates a dazzling glittering effect.

Any multi-coloured shimmer on animals such as hummingbirds or butterflies usually comes from their outer surface but this couldn't be the case with the fish as it's clear and has no scales.

However, experts in China have now found that with this species, the answer lies with the muscles of the fish!

How does the fish change colour?

The ghost catfish is a small freshwater fish that is native to rivers in Thailand in south-east Asia.

Apart from the head of the fish and its spine, it is completely translucent.

But when light hits the ghost catfish just right, its body shimmers with glistening rainbow colours!

Now, experts at China's Shanghai Jiao Tong University have worked out how this fish is able to create this iridescent glow.

How did the team make the discovery?

The team used a combination of scientific equipment including X-rays and laser lights for the study, which they shone on the fish.

They found that the catfish have unique muscles which are stacked tightly and can bend light into rainbow colours.

When the fish swim, their muscles relax and contract and create a glistening multi-coloured effect!

Even though other fish have similar muscle structures, the see-through body of the catfish means that the light can easily pass through it which creates this special illusion.

The team say that their new findings could explain how other see-through aquatic species such as eel larvae and icefishes, also appear rainbow-like.