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Strange New Glow-in-the-Dark Fish Identified

You would think that if you’re ugly, you’d rather hide in the dark shadows than call attention to your strange bulging eyes by having a glowing light in your stomach. But barreleye fish are OK with their looks and don’t even mind humans who taunt them with nicknames like “mirrorbelly tube-eyes.” Two new members of this mysterious species have been discovered and they’re anxiously awaiting their moment on the cover of Fish Vogue.

[It’s] one of the most peculiar looking and unknown deep-sea fish groups.

The group is the rarely seen barreleye family (Opisthoproctidae) which gets that particular nickname from their large tube-shaped eyes. The “mirrorbelly” nickname comes from their lighted stomach, which could have a much worse nickname since the light actually shines out of their rectal bulbs. (We would normally speculate on possible other nicknames here but children may be reading this).

three barreleyes

What was thought to be one species is actually three

Until now, it was thought that the family had 19 members but the total was difficult to verify because they were rarely examined alive (or freshly caught). The visual way to tell them apart was by the unique pigment patterns on their bellies which created distinct lights for each member. Oddly enough, the lights are actually used to camouflage the fish from predators swimming below by blending them into the small amounts of sunlight that penetrate the depths (thousands of feet below the surface) where they live.

Researchers from Greenland, Norway, Japan and the UK – led by zoologist and study author Jan Poulsen – were recently able to examine fresh specimens of barreleye fish from American Samoa and New Zealand and noticed three distinctly different pigmentation patterns on what was thought to be a single species. DNA analysis confirmed that they were looking at two new members of Opisthoproctidae – Monacoa niger and Monacoa griseus,

An illustration of the sole - the large flattened structure covered with large pigmented scales - and the light organ and reflector which control bioluminescence

Illustrations of the sole – the large flattened structure covered with large pigmented scales – and the light organ and reflector which control bioluminescence

This analysis of fresh specimens also revealed previously unknown yet dramatic color differences between juvenile and adult barreleye fish and shed new light (pun intended) on how and why the barreleye fish glow. Their luminous organ is deep inside their body and the light is actually reflected through the pigmented scales by another organ called the sole (nice family-friendly name for the rectal bulb). In addition to camouflage, the researchers now believe the light is also used for communication. (“You’re cute. Dive here often?”)

Can we learn from this unusual species of fish and celebrate our differences rather than stooping even lower than the depths of the ocean to resort to hateful name-calling?

Don’t hold your breath.