Weird fish of the week: Atlantic hagfish

There can be few weirder fish than the Atlantic hagfish. In fact it's so peculiar that some scientist argue it's not a fish, or even a vertebrate!

When the corpse of a dead whale or other large marine creature sinks to the ocean floor it's not long before a range of sea bed critters arrive and begin feasting. Among the first arrivals are hagfish and any dead dolphin or water-logged whale drifting to the bottom of the North Atlantic is likely to end up dish of the day for Myxine glutinosa, the Atlantic hagfish.

These are extremely primitive creatures with the earliest fossil record dating back to over 550 million years.

They have long, eel-like bodies, but no eyes or scales, just a single pair of external gill openings and their only fin is the caudal (tail) which extends along their back and belly.

The hagfishes' strange, jawless mouth is fringed with sensory barbels and in the absence of jaws their teeth are found on their tongue and palate. In many ways they are similar in appearance to the lampreys, which are believed to be their closest living relatives, but the hagfish is even more archaic with an entirely cartilaginous skeleton, only a partial skull and no vertebrae. This odd anatomy has led some to question if they can truly be considered vertebrates.

Another peculiar adaptation is their ability to produce huge quantities of slime as a defensive measure. Hagfish may lack the benefit of the lateral line sensory system of more modern fish, but in its place they have two lines of between 70 and 200 mucus and thread producing glands. When touched these produce a unique fibre reinforced slime that rapidly expands to cover the hagfish, making it hard to hold onto or swallow. Just take a look at the video below...

This glutinous discharge can clog the gills of predatory fish causing them to spit out the hagfish. The species scientific name refers to this with "Myxine" meaning slime or mucus while "glutinosa" just reiterates the point in case Greek's not your forte!

The hagfish has developed an odd way of cleaning itself of the slime once danger has passed. It twists into a rolling knot which strips the slime off its own body. This knotting behaviour has also been observed in feeding hagfish, and it is thought they use it to gain purchase on food to either rip off small pieces or to extricate themselves from inside carcasses as their gruesome feeding behaviour usually involves boring inside corpse to access the soft innards.

Hagfish will also take chunks out of living prey given the opportunity as well as feeding on small invertebrates and crustaceans. They can go months between meals thanks to a slow metabolism common to many deep sea inhabitants and spend much of their time hiding in the mud on the sea floor, waiting for their next meal to drop by.

Very little is known of their reproduction. Batches of up to 30 large, leathery eggs are laid which are stuck together with anchor like filaments on each end and possible parental care of these has been noted with adults seen curled around them.

Myxine glutinosa grow to a maximum length of around 80cm/32" and are very common throughout their range.

Why not take a look at some of our other Weird fish of the week features?