Deep-Sea Fish

Category: General Article

Back to Creep into the DEEPEND

Tuesday, August 25, 2015

Summary: Dr. Tamara Frank details the varied and amazing ways deep-sea fish find their food and hide from predators in a nearly lightless environment.

Hello Virtual Science Team,

Even though I’m part of Team Crusty, and we all know that crustaceans rule, I have to say that we’re catching some pretty cool fish. Team Fish is studying the fish ecosystem for the same reason that we’re studying the crustacean ecosystem. Like crustaceans, fish are major sources of food for a lot of the fish we like to eat, as well as whales, dolphins, seabirds, and other ocean animals. We need to know how fish were affected by the Deepwater Horizon oil spill back in 2010.

Team Fish has people work on identifying the fish and doing DNA studies. One reason they track the DNA is for something we call “population connectivity.” That means they’re trying to figure out if currents bring in fish from other locations, or does the entire population stay within the Gulf of Mexico.

We’re doing the same kind of studies with the crustaceans, but crustacean DNA is strong. That means we can extract back at the lab. Fish DNA is weak and has to be extracted on the ship. What this means is that the main taxonomists on Team Fish, Dr. Tracey Sutton and Dr. Jon Moore have to spend most of their time on the cruise looking under the microscope and identifying fish species.

Just between us, spending that much time looking under a microscope on a rolling ship would make me a little seasick. Since I don’t have to spend all of MY time looking through a microscope, I get to see some of the really cool fish that we’re catching, and tell you about them.

Deep-sea fish have some wonderful and unique adaptations to survive, find food, and avoid predators. They have some remarkable ways to hide in an environment where there’s nothing to hide behind. In the middle of the ocean, there are no trees, plants, bushes, rocks…it’s just water.

How do they find food when it’s so hard to see? Many deep-sea fish have light cells, called photophores, under their eyes they can use like a flashlight to see their prey. Take a look at the photo of the dragonfish in the slideshow to the right and you should be able to see the photophores around its eyes. The dragonfish’s photophore is red. That’s another cool thing about dragonfish. Most deep-sea animals cannot see red. But the dragonfish can. That means it can use it’s flashlight-like photophores to find prey, but the prey doesn’t know.

Why don’t most deep-sea animals see the color red? To find out that and more in this very cool video.

Video: Color And The Deep Blue Sea

Dragonfish also have a lure hanging off their chins that actually attract their prey to them. As soon as the prey gets close, they snap them up with their mouthful of big teeth.

Anglerfish are just as sneaky (see slideshow for images). They have a completely black body, which makes them hard to see in the dark deep sea. As you might know, the anglerfish dangles a little glowing lure in front of its mouth. Only the tip glows, so animals coming in to eat the glowing “prey” have no idea there’s a hungry fish with a big mouth and sharp teeth hiding behind the glow. An anglerfish is a “sit and wait” predator. That means that rather than chasing prey, an anglerfish waits for its prey to come to it.

Anglerfish have tiny eyes and no photophores, so they cannot really see much. They don’t need either because as soon as something touches the lure, they pounce. Anglerfish, like the dragonfish are completely black, so they blend in very well with the dark inky depths.

The viperfish also has a lure and huge teeth. It uses a different way to hide its body, though. It lives around 1,312 to 1,640 feet (400 to 500 m) down, where there’s a bit of light. That means that when it’s swimming along, its body blocks light. Potential predators or prey could see it as a dark shadow. To hide, hatchetfish are shiny, sort of like having mirrored sides. Any light blocked by the body is reflected back, so the fish basically disappear.

Shiny sides works fine for predators coming at them from the side, but what about predators below them? Like many deep-sea fish, the viperfish has photophores on its belly. The lights camouflage the fish by matching the light from the surface. The lights on their underside help them disappear into the light from above. It is an amazing kind of camouflage called “counterillumination.”

The hatchetfish also has wonderfully mirrored sides. But the hatchetfish has another way to hide from predators lurking beneath it. It is flat as a pancake! From the side, a hatchetfish might be 3-4 inches long and wide. But it is only ¼ inch thick. That means, when you look at a hatchetfish from the side, it is about the size of your palm. But it is only as thick as the nail on your pinky finger.

Some fish, like the waryfish have HUGE eyes. Extra-large eyes allow them to be as sensitive as possible to the tiny bit of light coming down from the surface.

Other fish might have tiny eyes, so they use other ways to sense or attract prey. Anglerfish are a great example of this. Notice how small its eyes are. Anglerfish don’t need their eyes because they attract prey to them.

Fish have something called a “lateral line.” The lateral line is on the side of the body and the head. It feels movement in the water. Think of it as a built-in motion detector. All fish have lateral lines, but in shallow water environments, where there may be many water currents, having a sensitive motion detector would drive a fish crazy. In the deep sea, where there’s very little water motion, having a sensitive lateral line system is probably better than having big eyes. The whalefish (see slideshow) is a great example. The whalefish has tiny eyes and huge lateral lines. Notice how the whalefish’s lateral line almost looks like a fancy tattoo. It can detect the motion of a small fish several meters away, so this is a very effective way of detecting both predators and prey.

These are just a few examples of the incredible deep-sea fish in the Gulf of Mexico. Hmm, I guess they’re almost as amazing as crustaceans!

Remember, if you have any questions, drop us a line. Talk to you soon,

Dr. Tamara Frank, Team Crustacean and Deep-sea Explorer



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