In the depths of the ocean, light can be a beacon or a dangerous temptation, attracting food and potential mates, but predators too. Noel Alfonso, an ichthyologist at the Canadian Museum of Nature, has collected hundreds of fish specimens from Canada’s waters, including several species of bioluminescent fish. He knows Canadian fish from the inside out, having been involved in x-raying species for taxonomy and even art over the past 23 years.

What is bioluminescence?
It’s a mechanism for creatures to produce light, which occurs when two compounds – one a luminescent protein, the other an enzyme – combine. It’s a widespread phenomenon in the animal kingdom, found in things as varied as fungi, insects, jellyfish and fish.

How do fish make use of it?
The primary way is finding and attracting prey. Bioluminescence happens in deep, dark water where it’s important to find something to eat. Another function is defence; some squid and shrimp produce flashes of light, which can confuse predators. Bioluminescence is also used for intra-species communication. When you’re in this environment, it’s important to find someone to carry on your genes, so the signals are often very species-specific.

What bioluminescent fish could humans see?
Lanternfish are quite abundant in oceans. If you were out late on a dark night, you’d likely see fish or some kind of ghostly glow. Everything else is pretty deep but, the lanternfish move up with their prey at night to feed. There are anecdotes about dense schools of lanternfish causing ships’ sonars to read false bottoms.

Are there a lot in Canadian waters?
There are. The Davis Strait is a hotspot for this because it has the necessary depth. It isn’t as rich as tropical waters, but that’s where they are. In Canadian waters, there might be 10 species that use bioluminescence.

Can bioluminescence work against a fish?
If a fish is blinking and trying to attract a mate, it may attract the attention of a predator. Like so much in life, it’s a gamble, but in general this mechanism works well for species – otherwise, we wouldn’t see it.

Five bioluminescent fish in Canadian waters

Marine hatchetfish
These fish, or several species of it that exist in the North Atlantic and Arctic, measure more in height than length. Because they live in a very dark environment, they often use bioluminescence in the form of vertical flashing bars to find a mate.

Photo: Argyropelecus gigas - Marine hatchetfish (Courtesy of the Canadian Museum of Nature)

Sloane’s viperfish
A fierce predator, the viperfish has a long dorsal ray (a long, string-like appendage) with a flashing light at the end. As the prey approaches, it swallows them. It basically uses its dorsal ray as a lure.

Photo: Chauliodus sloani – Sloane’s viperfish (Courtesy of the Canadian Museum of Nature)

Pelican gulper
Long and skinny, this fish is found in the Arctic and North Atlantic. Imagine a huge bulbous head with a thin body tapering off to a long tail with a light at the tip. As the prey is attracted by the light, the predator simply opens its large mouth and the suction action brings the prey in. It usually eats zoo plankton, crustaceans, copepods and possibly larval fish.

Photo: Eurypharynx pelcanoides – Pelican gulper (Courtesy of the Canadian Museum of Nature)

Glacier lanternfish
A species of the North Atlantic, this fish has a complex system of luminescence. When there is more than one species around, they have unique signalling that helps them find appropriate mates. They also use bioluminescence as a defence. If a predator swoops into a school, the lanternfish all flash an alarm to create a dazzling cloud of light to confuse predators.

Photo: Benthosema glacialis – Glacial lanternfish (Courtesy of the Canadian Museum of Nature)

The Northern giant sea devil
This anglerfish is found in the Arctic. They have a luminescent lure at the end of a dorsal ray. Females use the light to attract males. The male approaches the female, bites into her side and their vascular systems merge.

Photo: Ceratias holboelli – Northern giant sea devil (Courtesy of the Canadian Museum of Nature)