How do parrot fish make a mucus bubble?

Come sundown, this watermelon-sized Caribbean gem slips into a crevice and, using special glands behind its gills, secretes a bubble of mucus that swells up and over its head like a diving helmet. The pouch spreads towards the fish’s tail and, within 30 minutes or so, the fish is resting inside a surprisingly spacious sac of slime.

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Why do parrot fish make a mucus bubble?

The clammy cocoon – in which the fish spends the entire night – has many benefits. It is laced with antibiotics that kill known parrotfish pathogens, and also physically blocks blood-sucking parasites from getting near the fish. In addition, it appears to seal in the sleeper’s body odour, masking it from scent-tracking predators such as moray eels.

And the instant the pod is disturbed or torn, its owner wakes up and high-tails it out of there. It’s like a high-tech tent with a mosquito net and burglar alarm system.

But the queen parrotfish’s slimy behaviour doesn’t end there. Another gland constantly churns out a second type of mucus that protects the fish’s skin against ultraviolet light – like slime sunscreen. Most fish have it, but parrotfish can control where it goes. As it flocks to shallow-water
reef-tops each high tide to feed on algae, it slathers on about twice as much of the ointment over its top half as on the rest of its body. This allows the queen parrotfish to browse for food all day without burning its back, and also not waste the ‘sunscreen’ on parts where the sun rarely shines.

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Main image © Humberto Ramirez/Getty Images

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