Whence the Hagfish

The hagfish, (family Myxinidae, in the order Myxiniformes, in the class Myxini) that unlovable,  jaw-less, cartilaginous, slime-producing eel-like animal, is an extremely fascinating beast. Long considered to be a close relative of the lamprey at the base of the vertebrata, it is now considered to be a separate group, equally distant from both the jawed and other jaw-less fishes.

The details of this relationship are still under discussion, and the hagfish are being used to determine the ancestry of the vertebrates ancestral body plan. The Hagfishes are found in the family Myxinidae which contains 72 described species divided into 6 different genera, and are found in nearly all oceans of the world.

A majority of the species live in rather cold environments where the water is at least 20 meters (66 feet) deep. When hagfish live in warmer parts of the world, they are normally only found in really deep waters. Hagfish can survive at remarkable depths and have been found 1700 metres (5600 feet) down into the ocean.

The hagfish needs the salinity in its habitat to be stable, because these fishes have virtually no osmoregulation and are therefore highly vulnerable to salinity changes. The hagfish is the only known vertebrate with body fluids isosomotic with seawater. This means that the body fluids of the hagfish have the same total osmotic pressure or osmolality as seawater.

They are born hermaphroditic, but with maturation, one sexual form becomes dominant, while only remnants of the other sex organs remain. The various species range in size from 18 cm (roughly 7 ¼ in) to 127.5 cm (roughly 50 in).

Traditionally, the hagfish have been considered to be scavengers and parasites, feeding on carcasses and slow moving fish, that they devour from the inside.

Newer studies have however showed that the hagfish diet consists primarily of marine worms and other invertebrates, not large carcases. A majority of the typical hagfish diet is made up by worms from the Class Polychaeta (bristleworms). This doesn’t mean that hagfish will turn down an opportunity to feast on dead or dying animals; food is scarce deep down in the ocean and the hagfishes are certainly not finicky feeders. Dead and dying fish and other animals are an important source of nutrients for them and the hagfishes play an important role in the ecosystem of the sea by breaking down decaying animals that has sunk down to the sea floor. Hagfish will also happily eat fish caught in fishing nets, sometimes reducing the catch significantly for the fishermen.

They have also been observed entering the burrows of the red band fish, and emerging with their prey.

The slime produced by the hagfish, produced when the animal is threatened or disturbed, is a major and very successful defence against predators. The slime expands and fill the predator’s mouth within 1/2 a second.


In the videos, researchers did not film any successful predation on the hagfish, although remains have been found in the stomachs of fish with larger gills and in marine mammals.. In other words in animals where the slime could not impede the respiration of the predator.

As with many marine animals, the hagfish is being threatened in certain areas by over-fishing.

In most parts of the world hagfish is viewed as a useless by-catch, but there are a few countries in South East Asia where hagfish is appreciated on the dinner table.Nearly 5 million pounds (2 268 000 kg) of hagfish meat is for instance consumed in South Korea each year.

The tough and soft skin of the hagfish is also a popular commodity and is used to make wallets, purses, handbags, boots and similar items. The skin is normally market under the name “eelskin” or “eel skin”, not hagfish skin.

In Asia, over fishing has led to a significant decrease in the local hagfish population and Asian fisheries have therefore begun to show an interest in the hagfish populations in the Atlantic. While this might be beneficial for local economies along the Atlantic coasts, it could also pose a threat to the Atlantic hagfish population. Care and caution must be exercised unless we wish to see the Atlantic hagfish population go the same way as the Asian one. As mentioned above, studies indicate that the hagfish female only produces a low number of eggs each breeding period and hagfish are therefore extra sensitive to over-fishing.

Research is ongoing on hagfish in many areas. For example:

  • Their evolutionary status and their importance in understanding the ‘Tree of Life’.
  • The properties of their slime, which is fibre reinforced and as strong as spider silk.
  • The properties of their insulin, which is the most primitive known.

All in all, the hagfish, while repulsive by most standards, is a most interesting animal. Interesting enough to have its own ‘Hagfish day‘ (October 19). I’m late, but I can appreciate the hagfish all year round.

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