The mandarinfish is a small, brightly colored member of the dragonet family, native to coral reefs of the western Pacific Ocean. Their colours make them very popular in the aquarium trade, although don’t run off to buy one just yet – these fish are notoriously difficult to care for due to their highly specific diets. Mandarinfish also produces a thick protective mucus coating, which has a strong bitter smell.
But undoubtedly the coolest thing about these little fish is that they are one of only two vertebrate species known to have true blue colouring, i.e. colours that come from cellular pigment! I know, this sounds crazy doesn’t it? I bet you think you can name dozens of blue animals. But blue 💙is actually the rarest colour in nature – when we see a blue jay or a blue morpho butterfly, the colour comes not from the animals themselves, but from the way their external structures (wings, feathers etc.) reflect blue and violet light. This effect also happens to our eyes: if you have blue eyes, the colour is the result of microscopic structure of your iris, not pigmentation like in the case of brown eyes. So the pigments that makes the mandarinfish and it’s close relative the psychedelic Mandarin blue, called cyanophores, are the only true blue colours found in any living organisms on our planet!