The Jawless Hagfish

Hagfish at the Oklahoma Aquarium. It is difficult to see the individual fish. The small blue arrow is pointing at the head of one hagfish. The mouth is ringed by barbels, which look a bit like small tentacles. These were used for sensing their environments.

Recently, my family visited the Oklahoma Aquarium in Jenks, Oklahoma. It is a neat aquarium with many things to see. It had one thing in particular that I never expected to see, and that is hagfish.

The photograph above is one that I took at the aquarium. There is a whale jaw in there, but all of those long, coiled things are hagfish.

Hagfish live in deep waters, which are typically shrouded in darkness. That is why the light in the tank is red. Many creatures that are accustomed to darkness cannot see red very well, so a red light makes them visible while disturbing the animals as little as possible. Hagfish live as scavengers, eating flesh off of carcasses that drift down to the ocean floor, hence the whale jaw (which is probably a mock-up and not real).

An interesting feature about hagfish is that they lack jaws. They have mouths: they have an opening for eating, but they lack a moveable jaw. Thus, they cannot bite or chew their food. There are only two types of jawless fish alive today: the hagfish and the lampreys. The latter are parasites. They have sucker-like mouths and rasping tongues. They latch onto a fish, burrow a hole in the flesh, and suck out body fluids.

Hagfish have a very different way of eating. They also have tongue-like structures, but their tongues are lined with teeth. All of the rows of teeth both point upwards, and there are two pairs of rows, on opposite edges of the tongue. When a hagfish prepares to eat, it extends its tongue and folds its tongue down the middle, clamping a piece of flesh between its teeth. It can then retract its tongue, drawing the flesh in and swallowing it.

The head of the model of a hagfish. The tongue is protruding in this model: normally, it would be retracted into the mouth. Image from John Maisey (1996) Discovering Fossil Fishes, Henry Holt and Company, New York, New York

It is actually a bit more complex than that. The hagfish feed on large carcasses. Thus, they have to tear chunks of flesh off of these bodies in order to eat. The hagfish have a problem: they have no paired fins. Each hagfish has one fin, which runs around the tail, but they have no other fins. Thus, there is nothing projecting from the body that would allow it to brace itself while it tears chunks of meat off of a carcass. What does a hagfish do? It grabs onto a carcass with its tongue and wraps its body around its head, often wrapping itself into a knot. It then braces against the carcass with its body and pulls its head away, tearing off a piece of flesh.

Despite its appearance and way of life, hagfish are an important part of ocean ecosystems. As scavengers, they act as part of a waste disposal crew, cleaning up dead bodies on the ocean floor.

Thoughts from Steven