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Hagfish Facts: Strange Animals That Make an Intriguing Slime

Linda Crampton is a writer and experienced science teacher with an honors degree in biology. She enjoys writing about science and nature.

The head of a hagfish protruding from a sponge

The head of a hagfish protruding from a sponge

A Strange and Interesting Animal

The hagfish is a strange sea creature with a very elongated body. It looks somewhat like an eel but belongs to a different group of animals. Hagfish are jawless and are known for the large amount of slime that they produce. They are also famous for feeding on dead and dying animals—often from the inside of these creatures—and scraping the flesh off with their teeth, which are located on a movable cartilaginous plate.

Hagfish have one feature that is potentially very useful for humans. Their skin makes a sticky and protective slime that is made of mucus and strong threads of protein. Researchers hope to use the protein threads to make a fabric. The intact slime might be useful for us as well.

The slime of one species of hagfish is already used by humans. This animal is harvested in large numbers. People in some countries like to eat its flesh. Its skin is used to make a product that resembles leather, and its slime is used in place of egg white in recipes.

A Living Fossil

Based on the fossil evidence, the appearance of hagfish hasn't changed significantly for 300 million years. The animals are sometimes called "living fossils". They have a partial skull, which is made of cartilage, but they have no vertebrae. They have a rod known as a notochord instead of a bony spine. The notochord is made of a material resembling cartilage.

Hagfish are not invertebrates and are technically not fish either. They are classified in the phylum Chordata, as fish and humans are, but are placed in their own class (the Myxini). The members of the phylum Chordata have a notochord at some stage in their life cycle. In us, the notochord has been replaced by bony vertebrae by our early childhood years. In hagfish, it stays in place throughout the animal's life.

There's been considerable debate about the origin of hagfish. One theory says their ancestors were vertebrates (chordates which develop backbones made of vertebrae). The modern animal is said to be a form that degenerated and lost its ability to make vertebrae. The second theory says that the evolutionary line containing hagfish never developed the ability to produce vertebrae. The first theory is more popular among scientists today.

Hagfish are sometimes known as slime eels due to their shape and their production of copious amounts of slime. This name is not biologically appropriate, however, because eels are true fish and hagfish aren't.

The Body of a Hagfish

External Appearance

Hagfish are generally pink, blue grey, dark brown, or black in colour. They have three or four pairs of tentacle-like structures around their mouth and nostril. These tentacles are called barbels. They also have a white patch of skin where each eye is located.

The slime glands of a hagfish are visible as a row of white spots on each side of the body. The animals have no scales and have a skeleton made of cartilage. Unlike fish, they have no dorsal fin on their back and no paired fins. They do have a tail or caudal fin, however, which extends along the top and bottom of the animal for a short distance. The end of the body is flattened and looks like a paddle. The animal's skin is loosely attached to its body.

Sense Organs

The eye has no lens and no muscles, but it does have a simple retina containing light receptors. Hagfish can distinguish light from dark but can't see an image. They have an excellent sense of smell and a good sense of touch to compensate for their poor vision. They have a single nostril, which is located above their mouth and carries chemicals to the olfactory organ. The barbels contain touch receptors and may play a role in taste sensation as well. The animal hears via two inner ears.

In the video below, a scientist from the Scripps Institution of Oceanography discusses the hagfish that he studies.

Maximum and Minimum Length of the Animal

The Pacific hagfish (Eptatretus stoutii) lives in the eastern Pacific Ocean, which is my part of the world. An adult has an average length of about twenty inches. Some species are much longer and some are much shorter.

The goliath hagfish (Eptatretus goliath) is known from only one specimen discovered off the coast of New Zealand in 2006. The animal was a female and had a length of 4.2 feet. This is the longest hagfish known so far. On the other hand, the dwarf hagfish (Myxine pequenoi) seems to be about 7 inches in length. Its size is based on the two specimens discovered so far, which were obtained off the coast of Chile.

Highlights of the Animal's Internal Anatomy

  • Hagfish are said to have four hearts—one main one and three accessory ones. The main one is known as the branchial heart. The animal also has two pouches that act as a cardinal heart, a single pouch for a portal heart, and two pouches that act as a caudal heart.
  • The circulatory system is said to be semi-open. In some parts of the body, blood flows through blood vessels, but in other parts it flows through spaces called sinuses.
  • The animals breathe by means of gills. Water enters a hagfish's body through the nostril and travels through the nasal canal to the olfactory organ. It then passes through the nasopharyngeal duct to the gills, which are located in pouches. The gills absorb oxygen from the water and release carbon dioxide into it. After flowing over the gills, the water travels back to the ocean via one or more pores.
  • Hagfish have a digestive tract, which contains a gut but no stomach.
  • They also have a brain and nerves as well as a kidney for excretion. Both the brain and the kidney are considerably simpler in structure than ours.
A Pacific hagfish trying to hide under a rock

A Pacific hagfish trying to hide under a rock

Diet and Feeding Method

Hagfish live in burrows on the muddy sea floor, generally in deep water. Despite their reputation for invading and eating the bodies of larger animals, they eat mainly polychaete worms (relatives of earthworms) and other invertebrates found on the ocean bottom. They are predators as well as scavengers and have been observed entering burrows to catch fish. They are said to be able to go for months without food. Researchers have discovered that the animals can absorb some nutrients through their skin.

A hagfish feeds by a rasping motion, using teeth located on a plate of cartilage known as the dental plate. There are two rows of teeth on each side side of the plate. The teeth are made of keratin, a tough protein found in hooves, horns, nails, hair, and the outer layer of our skin. The dental plate acts like a rasping tongue and is both protractible (capable of being extended) and retractable.

Hagfish are often considered to be a nuisance by fisherman. When the fishermen haul in their catch, they sometimes find that the catch is only skin and bone and has hagfish inside.

Slime and Protective Behaviour

The slime of a hagfish is an excellent tool for defence. Immediately after being touched by a potential predator, the animal releases a large amount of slime. The material expands and forms thick, viscous sheets and strands when it mixes with sea water. It repels predators and can block the mouth and gills of predatory fish, suffocating them. If the slime of a hagfish enters its own nostril, the animal sneezes to get rid of it.

The hagfish exhibits another useful behaviour to defend itself against attackers. If a person or a predator picks up a hagfish and the animal can't escape, it twists its body into a knot. The knot begins at the head and progresses towards the tail. The knotting process helps to remove the slime off the surface of the animal's body, which is thought to repel the predator. The knotting process may also be useful at other times when a hagfish needs to remove an old slime layer from its skin. In addition, it may provide leverage when the animal is feeding, enabling the teeth to remove food from the prey more successfully.

When threatened or disturbed, (hagfish) spew out slime at the stunning rate of four cups in a fraction of a second.

— Christine Dell'Amore, National Geographic

Reproduction Facts

Not much is known about hagfish reproduction. The animal appears to start its life as a hermaphrodite, which means that it has both male and female reproductive organs. When it matures, one of the organs functions and the other doesn't. Research suggests that at least some hagfish can change gender during their lives.

It's thought that hagfish have external fertilization, although this isn't known for certain. Females lay eggs with a tough covering. The eggs have hooked filaments on each end, which helps them to become attached to objects. There is no larval stage. The eggs hatch into miniature adults.

Human Use of Hagfish Slime

People who encounter hagfish often consider the slime to be the most unappealing aspect of the animal. Scientists see great potential in the material, however. They hope to use the protein threads in the slime to make a strong fabric. Some Canadian researchers have already harvested slime from hagfish, mixed the material with water, and then spun the stretched fibers like silk.

Researchers have found that the protein threads in the slime of the Atlantic hagfish are 100 times thinner than a human hair and ten times as strong as nylon. They also have the advantage of being made by a "green" process, as opposed to fibres made from petroleum.

The strength and expansive ability of the slime is very interesting to researchers. According to a navy scientist exploring the material, it can expand to a volume that is nearly 10,000 greater than its original one once it enters water.

Though the protein threads on their own could be useful for us, the slime as a whole might be helpful as well. It has been suggested that it could act as a protective shield for divers. It might also be useful in the food industry as a gelatin substitute. Researchers are investigating the possibilities.

E. coli is used to make components of hagfish slime.

E. coli is used to make components of hagfish slime.

Genetic Engineering in Bacteria

Scientists don't plan to hunt or farm hagfish. Instead, they hope to genetically engineer bacteria to make the animal's slime. Some bacteria have proved to be very useful in making substances for humans once they have had the correct gene or genes added to them. Preliminary experiments in using hagfish genes in bacteria have already been successful.

In 2017, U.S. Navy scientists announced that they had isolated the genes that make two important proteins in the slime. They inserted the genes into two groups of Escherichia coli (or E. coli) bacteria. The genes became activate in the bacterial cells, and the bacteria made the proteins. The scientists were able to confirm that these were in fact the same proteins made by the hagfish.

Scientists in Singapore reported similar results with engineered E. coli in 2015. The discoveries could be very significant. Hagfish slime is believed to consist mainly of mucus mixed with the protein filaments that are produced by E. coli.

In July, 2017, a truck in Oregon carrying thousands of living hagfish dropped its load on a road. The stressed animals created a huge mass of slime, as can be seen below. The animals were going to be shipped to Korea as a food source.

Other Uses of the Animals

The inshore hagfish of the northwest Pacific Ocean (Eptatretus burgeri) lives in much shallower water than its relatives. Its flesh is used as food in Korea. The skin of the animal is known as eel skin and is used to make items such as belts, accessories, and clothing.

Strange or unpleasant as it may sound, the slime of the inshore hagfish is sometimes used as a substitute for egg white in recipes. The slime is said to be obtained by banging a stick on a tank containing a living animal.

This species is used so intensively that its population is decreasing and the IUCN (International Union for Conservation of Nature) classifies it as "Near Threatened". This classification was made in 2009, however. The situation may have changed—for better or worse—since then. Even the IUCN says that the animal’s status needs to be updated.

Successful Creatures

Hagfish are sometimes considered to be primitive creatures, but their slime has enabled them to be very successful animals. They are believed to have existed almost unchanged for millions of years. Their habits may seem disgusting to us, but they are very helpful for the animals and have been a wonderful survival mechanism.

Most hagfish live in deep water and are hard to study in their natural environment. There is still a lot to be learned about these fascinating creatures and their successful lives. The effort to discover more about them should be very worthwhile. The discoveries may satisfy our curiosity about the animals and may also be useful for us.


© 2012 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on January 18, 2013:

You've raised a good point, Sasha - a "hag gown" doesn't sound very appealing! A new name would definitely have to chosen for any fabric made from hagfish slime! Thanks for the comment and the votes.

Aloe Kim on January 18, 2013:

How fascinating ^_^ Thanks for the great read. I wonder if they made a fabric out of hagfish... would they disguise the name? I don't think designers would flaunt "hag gowns" ^_^ voting up and interesting!

Linda Crampton (author) from British Columbia, Canada on December 27, 2012:

Thank you very much for the comment, Peggy. I appreciate the vote and the tweet!

Peggy Woods from Houston, Texas on December 27, 2012:

This is fascinating Alicia. Hagfish are useful as scavengers from watching that one video where they were feeding off of a deceased whale body on the ocean floor. I had never even heard of a hagfish prior to reading this. Thanks for writing such an informative hub! Up votes and tweeting.

Linda Crampton (author) from British Columbia, Canada on December 24, 2012:

Thank you for the comment, macteacher. I enjoy learning about new creatures too! There is so much that is unknown about ocean life, especially life in the deep sea habitat. It's a fascinating area to explore.

macteacher on December 24, 2012:

I love learning about new creatures, and this one is fascinating. It looks a little disgusting, but I'm sure to marine life - us humans look a little disgusting. It's amazing, with all of our technology, how little we know about deep sea creatures. Thanks for a fascinating hub about an unusual animal.

Linda Crampton (author) from British Columbia, Canada on December 20, 2012:

Thank you for the comment, unknown spy. Yes, the hagfish does look somewhat like a snake. It has an unusual appearance!

DragonBallSuper on December 20, 2012:

scary..looks like a snake. great hub about this strange animal.

Linda Crampton (author) from British Columbia, Canada on December 13, 2012:

Thanks for the visit, Dianna. I agree - the hagfish does have a purpose and is an important part of its ecosystem. It will be interesting to see whether thread and fabric made from hagfish slime are eventually sold commercially !

Dianna Mendez on December 13, 2012:

I wouldn't want to touch one - unless necessary. It does have its purpose in life as it contributes to the animal kingdom. Interesting that it is being considered as threads for fabric. Enjoyed the read.

Linda Crampton (author) from British Columbia, Canada on December 10, 2012:

Thank you for the visit and the comment, Deb! I'm glad that hagfish have survived, too. They are fascinating animals, and their slime is very interesting.

Deb Hirt from Stillwater, OK on December 10, 2012:

I'm glad that they have been able to survive for so long. So many animals are nearly extinct. Thanks for the fantastic info, Alicia!

Linda Crampton (author) from British Columbia, Canada on December 10, 2012:

Thank you very much for the comment and the votes, Seeker7! Yes, the hagfish has been very successful, even though it doesn't have the characteristics of more advanced animals. It's an interesting creature!

Helen Murphy Howell from Fife, Scotland on December 10, 2012:

What a fascinating article. I had heard of hagfish from TV documentaries but I didn't know the half - especially about how useful their slime might be! Also the 'goliath' hagfish - that's huge compared to what I thought their size might have been! I guess they are seen as being primative, but then, if an animal is so successful with what they have, why change?

I really enjoyed this fascinating hub - voted up awesome!!

Linda Crampton (author) from British Columbia, Canada on December 10, 2012:

Thank you very much, drbj! I appreciate your great comment. I wouldn't mind touching a hagfish, but I'd have to prepare myself mentally before doing this!

drbj and sherry from south Florida on December 10, 2012:

I've never touched a hagfish, Alicia,

In fact I seldom SEE one.

But I can tell you this, m'luv,

I would rather touch than BE one.

Fascinating, awesome and outstanding in amount of information and relevant photos and videos. Thank you and an Up to you.