Hagfish

Hagfish, also known as slimy eels or slime eels, are so named because they produce slime. However, they are not actually eels but eel-like fish that have jawless mouths, like the lampreys. They are important for commercial and food purposes, and their habitat is all the world’s oceans, with each species having a different range.

5 Incredible Facts

• Hagfish are the only animals that have a skull but no spinal column, although they do have rudimentary vertebrae.
• They can absorb nutrients through their skin.
• Their slime allows them to escape capture when they tie themselves into an overhand knot.
• Their slime clogs up marine predators’ gills, suffocating them so they will release the hagfish.
• The hagfish’s loose skin allows for whole-body flexibility, which allows it to tie itself into knots without injury.

Classification and Scientific Name

The hagfish belongs to the subphylum Vertebrata because, although they have no spinal column, it has rudimentary vertebrae. Then the hagfish is in the superclass Cyclostomata and the class Myxini; however, they were once in the historical class called Agnatha, for jawless fish (agnathans), with lampreys. Classification names and members have been adjusted through the years as more is learned about the various life forms and their characteristics.

The order is Myxiniformes. There is only one family of hagfish, Myxinidae, but there are six genera. Sometimes, they are classified into two families, the other being Eptatretidae. All the species have the common characteristics of a jawless mouth and a cartilaginous skull with no spinal column.

The six genera are: Myxine, Eptatretus, Paramyxine, Notomyxine, Neomyxine, and Nemamyxine.

There are currently 76 recognized species of hagfish, though the number may change as new species are discovered. The most studied species, with the scientific name Myxine glutinosa, is the Atlantic hagfish. Examples of other species are the Goliath hagfish (Eptatretus goliath), Pacific or California hagfish (Eptatretus stoutii), and the black hagfish (Eptatretus deani).

There is a hagfish fossil from 300 million years ago, and scientists think that the hagfish has not changed much in all that time.

Appearance

All the hagfish species have the common characteristics of long, slender bodies with a pinkish-grey, blue, or purple color depending on the species, and sometimes covered in spots. They also produce a thick, sticky slime from 100 glands on both sides of their bodies. Their weight ranges from 0.85 to 1.4 kg (1.8 to 3.1 lb) with a length of 4cm (1.6in) to 81.28cm (32in), but typically 50cm (19.7in).

There are several other unique characteristics:

• Hagfish are one of the few animals that have multiple hearts. They possess three accessory hearts, no cerebrum or cerebellum, a single nostril, and a cartilaginous skull.
• They have a tooth plate that protracts and retracts instead of jaws; 2 parallel rows of rudimentary, pointed teeth, which repeatedly get reabsorbed and regrown; a rasping tongue; and a horizontally moving, funnel-shaped mouth.
• Hagfish have several pairs of tentacles in various places on the body that serve mechanosensory and chemosensory functions.
• They have a reduced pair of eyes appearing as pigmented spots on the back of the head behind the oral region, under the translucent skin, and in front of the gill-bearing branchial region.
• What differentiates these fish from eels is the lack of paired fins, since they have only the caudal (tail) fin.
• Internally, their respiratory system is unique, with the presence of a sinus system through which the organs absorb blood from the veins and other blood vessels.
• They have no stomach, but the food they consume is instead enclosed in a permeable membrane.

The Atlantic hagfish can grow up to 95 cm (37.4 in) in length, while the Goliath Hagfish, the largest species, can reach 127.5 cm (4 ft, 4 in). Myxine kuoi and Myxine pequenoi reach up to 18 cm (7.1 in), while other species are as small as 4 cm (1.6 in).

The species of the genus Eptatretus are seven-gilled hagfishes. The Atlantic and Pacific hagfish differ in two ways: The Atlantic hagfish has muscle fibers in its skin, and its resting position is stretched, while that of the Pacific hagfish is coiled.

Behavior

Although the thick, sticky substance hagfish produce is called slime, it’s actually not. Its characteristics are instead a milky, fibrous mucus. The species Myxini glutinosa was named for it, with the word “glutinosa” in Latin meaning glutinous or gummy. Hagfish produce slime while they eat, while burrowing, or while escaping from predators, in conjunction with an overhand knot from head to tail. Hagfish slime has been explored as a substitute for egg whites, particularly in Korea, but its use in this way is not widespread.

Since hagfish live on or near the bottom of the ocean floor, fishing is difficult near them. They can spoil or consume the catches within the fishers’ deep dragnets before they can pull them to the surface.

Distribution, Population, and Habitat

While many hagfish species are classified as Least Concern, about 12% are considered threatened according to recent assessments. Hagfish are present in oceans around the world. All species live in cold saltwater, with their range varying depending on the species and the ocean. The habitat of the species in the Eptatretus genus is the Pacific Ocean, with that of the Far Eastern inshore hagfish (Eptatretus burgeri) being the Northwest Pacific. The habitat of the Myxinidae family is all the world’s oceans, and that of Eptatretidae is everywhere except the North Atlantic. They burrow into the ocean floor or into dead and dying fish, living in cold, low waters with a temperature of 15°C and a depth range of 52-5,600ft (15.85-1,800m), but typically 4,000ft (1,219m).

Predators and Prey

Hagfish are scavengers and parasites, with a carnivorous diet. They prefer to feed on or parasitize live prey, although they will scavenge on dead or dying creatures when given the opportunity. Their rasping tongues pull the prey into their mouths.

Hagfish typically feed on bottom-dwelling worms and other invertebrates, whales, and fish. They can absorb nutrients through their skin and produce slime when they feed.

Hagfish have few marine predators because of their slime, which helps them to escape predators, as well as the ability to squeeze through openings that are less than half their body width, which not only helps them to escape predators but also to scavenge. Their predators are mostly varieties of birds and mammals, with humans posing a threat to 20% of hagfish species, according to the IUCN.

Reproduction and Lifespan

Hagfish are a sexually dimorphic species with a ratio of up to 100:1 in favor of females. Some species are hermaphroditic. Females lay anywhere between 1 and 30 tough eggs that stick to each other with Velcro-like ends. The gestation period is typically 11 months, and there is no larval stage, unlike lampreys. Not much else is known about their reproductive behavior due to the difficulty in laboratory breeding. Regardless, they can live up to 40 years in the wild and 17 in captivity.

Fishing and Cooking

Hagfish have important commercial uses.

For one, they are eaten in Korea and Japan. In Korea, they are typically skinned before being grilled or stir-fried and are considered an aphrodisiac by men. In Japan, hagfish serve as an alternative to tofu, due to the slime that can bind a large amount of liquid with little to no heating. Hagfish are caught by fishers in California, but most of the catch is exported to Korea, and they are rarely available for direct purchase by consumers in the United States.

Hagfish flesh is chewy with a mild yet distinct taste and an unpleasant aftertaste. To prepare Korean-style, slice down the middle, remove the digestive tract, and marinate in Korean barbecue sauce. Place the raw fish on a hot plate and cook, slicing with scissors, and serve the cooked fish with lettuce and gochujang (red chili paste). The head is typically left on the fish and offered as an honor to guests. While hagfish can be eaten raw, it is far more commonly cooked before consumption.

Hagfish skin is used as a durable leather in several clothing accessories, including wallets, belts, and shoes. It is typically called “eel skin.”