The Hagfish: A Strange Animal with a Useful Slime or Mucus
A Strange Creature
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. The mucus contains strong threads made of protein. Researchers hope to use the threads to make a fabric. One species of hagfish is useful for other reasons and is harvested in large numbers. People in some countries like to eat the flesh of this animal. The skin is used to make a product that resembles leather and the slime is used in place of egg white in recipes.
A Living Fossil
Hagfish are sometimes called "living fossils". Based on the fossil evidence, their appearance hasn't changed significantly for more than 300 million years. 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.
Hagfish are not invertebrates and are technically not fish either, though they are often referred to by this name. They are classified in the phylum Chordata, as fish and humans are, but are placed in their own class—the class Myxini. The members of the phylum Chordata have a notochord at some stage in their life cycle. In us, the notochord has been completely replaced by vertebrae by our early childhood. 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) and the hagfish represents a degenerated form that lost its vertebrae. The second theory says that the evolutionary line containing hagfish never developed 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, though, 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 color. They have three or four pairs of tentacle-like structures around their mouths and nostril. These tentacles are called barbels. Hagfish 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 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 hagfish hears via two inner ears.
Hagfish have four hearts—one main one and three accessory ones. They have a gut but no stomach. They 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.
Maximum and Minimum Length
The hagfish of the eastern Pacific Ocean (my part of the world) is known as the Pacific hagfish (Eptatretus stoutii). An adult has an average length of about twenty inches. Some species are much longer and some are much shorter than this.
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.
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, hagfish 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, however.
Hagfish are often considered a nuisance by fisherman, since when the fishermen haul in their catch they may find that the catch is only skin and bone and has hagfish inside.
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 protractable and retractable.
Slime and Protective Behaviour
The slime of a hagfish is an excellent tool for defence. Immediately after being touched by a potential predator, a hagfish releases a large amount of slime. The slime 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 nostril, the animal sneezes to get rid of it.
The hagfish exhibits another useful behavior 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 hagfish'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.
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. A hagfish 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 hagfish.
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 hagfish slime. They hope to use the protein threads to make a strong fabric. Some Canadian researchers have already harvested slime from hagfish, mixed the slime 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 hagfish slime is very interesting to researchers. According to a navy scientist exploring the slime, it can expand to a volume that is nearly 10,000 greater than its original one once it enters water.
E. coli is a rod-shaped bacterium that is often used in genetic engineering experiments. The bacterium exists in the form of different strains. Some strains are beneficial for us and others are harmful.
Genetic Engineering in Bacteria
Scientists don't plan to hunt or farm hagfish. Instead, they hope to genetically engineer bacteria to make hagfish 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 hagfish genes that make two important proteins in hagfish slime. They inserted the genes into two patches 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 proteins made by the hagfish.
Scientists in Singapore reported similar results wih engineered E. coli i. 2015. The discovery could be very significant. Hagfish slime is believed to consist mainly of mucus mixed with filaments made of the proteins produced by E. coli.
Other Uses of the Animals
The inshore hagfish of the Northwest Pacific Ocean (Eptatretus burgeri) lives in much shallower water than other hagfish. 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 hagfish.
This hagfish is used so intensively that its population is decreasing and the IUCN (International Union for Conservation of Nature) classifies it as "Near Threatened".
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 hagfish 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