The mysterious fish of the deep sea have long captured the imagination, and even now, scientists continue making exciting discoveries about the animals that dwell in the deepest parts of our planet. One such creature is the flashlight fish (Anomalops katoptron), an otherworldly specimen that we’re lucky enough to have on-site here at Tynemouth Aquarium.
From its name alone you may be able to guess this fish’s party trick. The flashlight fish is capable of emitting light from two bioluminescent organs beneath its eyes, which it uses to communicate with its school, evade predators, and attract prey and potential mates alike.
But how exactly does a flashlight fish create light? Why do they do it? And what can this behaviour tell us about life in the depths of our seas and oceans?
Join us as we take a deep breath and plunge into the wonderful world of the flashlight fish, finding out more about how and why this fish puts on one of the ocean’s most captivating visual displays.
Before we launch into the science-y stuff, let’s take a closer look at the need-to-know details about the flashlight fish, so you can get an idea of where this fish lives, what it eats, and what it looks like.
Flashlight fish are a relatively small species, growing to a maximum size of around 24cm. An average-sized specimen should just about fit in an adult hand.
The fish are dark brown and grey in colour, with a distinctive spotted line that curves along the length of their bodies. They have a large dorsal fin and a split tail fin, as well as two bioluminescent organs which appear beneath their eyes in a sort of teardrop shape.
Flashlight fish live in the Indo-Pacific region, from the Great Barrier Reef off the coast of Australia to the tropical atolls of the Indian Ocean. Although they spend much of their lives in the depths, they are one of the few deep sea fish that come to the surface, seeking the comfort of warmer waters in the winter months.
What do flashlight fish eat?
The flashlight fish is a tactical luminescent predator that attracts prey by blinking the lights beneath its eyes. Its diet consists of small fish and invertebrates.
Many creatures of the deep sea use bioluminescence to navigate their environment, attract prey, and communicate with other fish. But few exhibit this behaviour in quite so spectacular a fashion as the flashlight fish.
Biologists estimate that the bioluminescence of the flashlight fish is so bright, it can be seen from over 30 metres away – an impressive feat in the murky blackness of the deep sea. It’s thought that they use these bright lights predominantly to catch prey, using a series of blinks to attract attention, before going in for the kill.
But the question remains: how do flashlight fish make light?
Time for some science. The light-emitting organs that appear beneath a flashlight fish’s eyes contain millions of bioluminescent bacteria, which together produce a bright green light. This kind of bacteria is present in lots of other animals, from other deep-sea fish to creatures like fireflies found on the earth’s surface.
If you think the presence of light-emitting bacteria in a fish’s face is impressive, wait until you hear about the animal’s next trick. Believe it or not, flashlight fish are able to manipulate this bacteria to switch the light on and off at their choosing. They do this simply by “rotating” the bacteria inwards and outwards – pretty neat, right?
And this isn’t a slow or random process, either. The fish are capable of blinking their bioluminescent lights up to 75 times a minute, with scientists concluding that they use different sequences depending on whether they’re attracting prey, evading predators, or communicating with one another.
By now you should have a pretty good idea about why it is that flashlight fish glow. Not only does their bioluminescence help with navigating through the inky black of the deep sea, but it’s also essential for attracting prey and escaping from predators.
In recent years, however, scientists have made a series of exciting new discoveries about the glow of the flashlight fish. Observing the animals in relatively shallow waters off Mborokua Island, a volcanic islet in the South Pacific, biologists recorded new behaviour which sheds more light on how and why deep-water fish like the flashlight use bioluminescence.
Hundreds of flashlight fish were seen using their bioluminescence in a school, presumably to help remain in a well-organised group during a hunt or in a combined effort to avoid nearby predators. This behaviour is particularly surprising since it’s long been believed that flashlight fish – like other deep-water species – are solitary, raising questions about what life is really like in the depths of our oceans vs our preconceptions.
Here at Tynemouth Aquarium, we’re lucky enough to have a small handful of flashlight fish in our collection, which you can see in all their bioluminescent glory at our unique deep-water exhibit, The Abyss.
Since flashlight fish are extremely sensitive to light, this purpose-built exhibition space is maintained in complete darkness. That means, as you navigate the room, the otherworldly glow of the flashlight fish will be the only light you can see. We promise it’s a truly magical experience that you’re unlikely to ever forget!
We hope you’ve enjoyed this introduction to the enchanting flashlight fish and that it’s helped you learn more about the wonderful species of our deep seas. If you’d like to stand in the glow of the flashlight fish yourself, book your tickets to Tynemouth Aquarium today.