Australasian Science: Australia's authority on science since 1938

Fish Slimed to Death

By Stephen Luntz

Hagfish filmed choking predators with noxious slime.

Hagfish are not known as beautiful creatures, but their reputation as something to avoid has been enhanced with the discovery that they choke predators with noxious slime.

A/Prof Euan Harvey of the Oceans Institute at the University of Western Australia was part of a team that filmed members of the ancient genus releasing slime to repel sharks and bony fish.

Marine biologists have rated the hagfish the most disgusting creature of the seas. However, the 550-million-year-old-eel-like survivors probably don’t care. As the only living creature with a skull but no vertebral column, the hagfish has attracted debate as to whether it should be categorised as a fish at all.

Hagfish also lack image-resolving eyes or fins, so they need something to give them a competitive advantage, and that something is slime. When alarmed they will produce large quantities of the slime, which turns to gelatinous goo in water.

It has been speculated that the slime is used to clog the gills of potential predators, perhaps explaining why the hagfish is known to be eaten by marine mammals and birds but not fish.

A joint Australian and New Zealand team deployed stereoscopic cameras near the seabed off New Zealand’s Great Barrier Islands. On 14 occasions they witnessed predators attacking hagfish that had been attracted by the bait. “As soon as it is attacked, the hagfish releases a mucus-like substance from a battery of slime glands, which makes predators gag before quickly retreating,” Harvey says.

The footage is available on YouTube and was watched more than 100,000 times barely a week after it was uploaded.

Hagfish have adapted to the danger that they might slime their own gills in a remarkable way. They can tie themselves in a knot that works its way from head to tail, scraping their body free of slime in the process.

However, the footage revealed a further development, with one hagfish ignoring the bait to chase a small fish down a hole. The hagfish appears to have suffocated the fish in its burrow, at which point it knots its own tail, which Harvey believes is to gain leverage so it can pull itself out of the hole, bringing the dead fish with it.

“This is the first evidence hagfish are predators as well as scavengers, which is very exciting,” Harvey says.