The wrought-iron butterflyfish is the most metallic of all fish


Bec Crew


Bec Crew

Bec Crew is a Sydney-based science communicator with a love for weird and wonderful animals. From strange behaviours and special adaptations to newly discovered species and the researchers who find them, her topics celebrate how alien yet relatable so many of the creatures that live amongst us can be.
By Bec Crew April 27, 2020
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Meet the wrought-iron butterflyfish.

Animal Crossing would have us believe that the black bass is the most metal fish in the ocean, but it doesn’t even come close to the wrought-iron butterflyfish. This fish looks like it’s been cast in silvery black iron, its patterning reminiscent of a newly forged sheet of chainmail.

Native to the western Pacific ocean, near central and southern Japan, the wrought-iron butterflyfish (Chaetodon daedalma) can grow to 15 cm long, which is half the length of the world’s biggest butterflyfish – the lined butterflyfish (Chaetodon lineolatus) and the saddle butterflyfish (Chaetodon ephippium), which can be found along the north, east, and west coasts of Australia.

While wrought-iron butterflyfish tend to move around in pairs or groups of three or five, lucky divers will occasionally come across a ‘wrought-iron ball’. This phenomenon occurs when huge numbers of the fish congregate to graze, undulating in tight formation, knowing they’re safer among hundreds than alone.

Despite experts noting their playful nature, one describing them as “one of the most personable butterflyfish there is,” their restricted range makes them a rare sight in collections and in the wild.

Here’s some footage, which shows just how cool those bright yellow fin-tips are:

The wrought-iron butterflyfish is unusual among the Chaetodon family of butterflyfish for their stark black colouration. Similar to angelfish, another large group of tropical marine fish, butterflyfish are typically characterised by their vibrant colours and striking patterning.

Australia is home to some fantastic species, such as the threadfin butterflyfish (Chaetodon Auriga) and the vagabond butterflyfish (Chaetodon vagabundus), both known for their distinct chevron patterns:

(Image credit: Roberto Nistri / Alamy Stock Photo)

Then there’s the dusky butterflyfish (Chaetodon flavirostris), an east coast species with a smoky-grey-to-yellow transition similar to the wrought-iron butterfly fish’s colouring.

I’ll leave you with a species from further afield, out around Hawaiian Islands. This is the tinker’s butterfly (Chaetodon tinkeri), which barely even looks real: