Hagfish: Strange Animals That Make an Intriguing Slime
A Strange and Interesting Animal
The hagfish is a strange sea creature with a very elongated body. It looks something 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 In us, the notochord has been replaced by bony vertebrae by our early childhood years.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
Hagfish are generally pink, blue grey, dark brown, or black in colour. They have three or four pairs of tentacle-like structures around their mouths 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.
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
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 than ours.
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 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
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 help 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. However, scientists see great potential in the material. 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.
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 filaments of the proteins produced by E. coli.
In July, 2017, a truck in Oregon carrying thousands of 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. The situation may have changed—for better or worse—since then.
Would you be willing to touch a hagfish?
Hagfish are sometimes considered to be primitive creatures, but their slime has enabled them to be very successful animals. They 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 very successful lives. The effort to discover more about them should be very worthwhile.
© 2012 Linda Crampton