Two new species of glowing spook fish discovered

by Shreya Dasgupta on 22 August 2016

Barreleyes, with their large transparent heads, are one of the rarest and “most peculiar and unknown fish groups in the deep-sea pelagic realm”, researchers say.
Some barreleyes have special organs on their bellies called “soles”, covered with pigmented scales, that reflect light emitted from luminous organs inside their bellies.
By comparing the pigment patterns on the soles of barreleyes fish collected near American Samoa and New Zealand with long-preserved specimens previously caught near the mid-Atlantic ridge and Australia, researchers found that two species are new to science.

Scientists have discovered two new species of bioluminescent deep-sea fish off New Zealand.

Both species belong to the family Opisthoproctidae, also known as spook fish or “barreleyes”, named for the protruding cylindrical eyes that point upwards to detect the silhouette of prey, according to a study published in PLoS ONE.

Barreleyes, with their large transparent heads, are one of the rarest and “most peculiar and unknown fish groups in the deep-sea pelagic realm”, researchers write in the paper. Only 19 species are currently thought to be a part of this family of fish.

Some barreleyes also have special organs on their bellies called “soles”, which are covered with pigmented scales. These soles act as reflectors, deflecting the light emitted from luminous organs inside their bellies. Scientists believe that in the slightly sunlit depths of water, where barreleyes are typically caught, the fish might be using the light reflected by the soles for counter-illumination to camouflage themselves, and possibly for communication. The Barreleyes are sometimes referred to as mirrorbelly tube-eyes because of their reflecting bellies.

Using pigment patterns on the belly soles of the fish, scientists identified two new species of deep-sea barreleye fish (top). Image credit: Poulsen et al. (2016).

By comparing the pigment patterns on the soles of barreleyes fish collected near American Samoa and New Zealand with long-preserved specimens previously caught near the mid-Atlantic ridge and Australia, researcher Jan Yde Poulsen from the Australian Museum, Sydney, and his colleagues, found that two species are new to science.

The researchers have grouped the two species under the genus Monacoa, and named them black mirrorbelly (M. niger) and grey mirrorbelly (M. griseus) for the pigment patterns on their bellies.

“This new study on the deep-sea has shown unknown biodiversity in a group of fishes previously considered teratological variations of other species,” Jan Poulsen said in a statement. “The different species of mirrorbelly-tube eyes can only be distinguished on pigmentation patterns that also constitutes a newly discovered communication system in deep-sea fishes.”

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