Deep in the ocean is an ancient fish that glides along by flapping their wing-like pectoral fins instead of swishing their rattish tail. They look similar to a shark but with bigger eyes, a more protruding snout and only one visible gill opening.
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These are chimaeras, also known as ghost sharks, rat fish and rabbit fish. They diverged from sharks and rays around 400 million years ago but around 50 species can still be found in our seas today.
What is a chimaera?
Also known as ghost sharks, chimaeras are not true sharks but are very similar to sharks and rays and have a common ancestor – these cartilaginous fish split off from elasmobranchs around 400 million years ago. There are around 50 known species of chimaera but, because they tend to live in very deep waters, scientists still have lots to discover about them.
What do they look like?
Chimaeras look like a bunch of different animals, which might explain why they have so many common names. These strange fish have large eyes and pale, sometimes nearly translucent skin that makes them look rather eerie, hence them sometimes being called ghost sharks or spookfish. They have long, thin tails like a rodent (they are also known as rat fish) and prominent front teeth like a bunny (you guessed it, they’re also sometimes referred to as rabbit fish).
The combination of all these different features is also why they are called chimaera. The name is a nod to the Chimera from Greek mythology: a fire-breathing mash up of a lion, a goat and a serpent.
How big are chimaeras?
They range from 60cm to 2 metres in length depending on the species and usually weight up to around 4kg.
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Where do Chimaeras live?
Chimaeras live in every ocean except the polar regions. Although some species can be found in shallower waters, they usually live hundreds or thousands of metres deep. Because they feed on animals that hide in the seabed, ghost sharks spend most of their lives close to the seafloor, typically, between 200 and 2,600 metres.
What do they eat?
They find and snaffle small animals hidden in the seabed, such as crabs, worms and sea urchins.
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How do Chimaeras hunt?
Chimaeras have a prominent snout covered in electroreceptors. Like sharks, this network of sensory pores – known as ampullae of Lorenzini – can pick up tiny electrical currents in the water and help the animal detect hidden prey.
Because a lot of their prey are invertebrates with hard exoskeletons, these fishes have three pairs of strong tooth plates designed for crunching through the shells.
True sharks constantly lose their teeth through their lifetime and grow new ones to replace them. But chimaeras just keep growing their teeth plates throughout their lifetime to repair the wear and tear from grinding tough shells.
How do they reproduce?
Like some species of sharks, ghost sharks lay eggs. The strangest thing about their reproduction lies right in the middle of their forehead. Male chimaeras have a retractable organ called a tenaculum on their head. This little nubbin is covered in tiny tooth-like scales called denticles which help the male grab onto the female during mating.
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Are they dangerous to humans?
Generally, no. Chances are you’ll never see one of these deep-sea ghost sharks in your lifetime and, if you did, they’d be much more interested in chomping on their usual prey – small critters living on the seabed – than bothering to target you.
However, they will defend themselves if they need to. Deep-sea fishers have been injured by the sharp, venomous spines on these fishes with wounds sometimes having to be dealt with under general anaesthetic.
Are they under threat?
Yes. A 2024 report highlighted that one third of sharks, rays and chimaeras around the world are threatened with extinction, largely because of overfishing. Although there isn’t much data on the conservation status of these little-studied animals, some scientists are concerned that populations may be struggling.
