Happy Halloween – Here’s Your Ocean Werewolf

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

What better way to kick off Halloween morning than with the werewolf of the sea… This is the Atlantic wolffish (Anarhichas lupus), very appropriately and otherwise known as the 'devil fish', and also more adorably the ‘sea cat’.

They’re pretty hefty fish, growing up to 1.5 metres long and over 20 kg, and they're named for those unmistakable fangs. They have 4-6 long, sturdy canine teeth on both their upper and lower jaws, and behind these sit multiple rows of molars for very efficient crushing. Oh and their throats are lined with a spattering of small, serrated teeth - all the better to destroy the hardened exteriors of mollusks, crustaceans, and echinoderms.

While many species of fish regularly replace their worn-down teeth with new ones, Atlantic wolffish only get new teeth once a year, so they spend a part of every year toothless and hungry while they wait for the new ones to come through. During this mandatory fasting period they go from being fat and happy to being very thin and very poorly. Once their new teeth have toughened up - sea urchins, beware! - they will go on a huge, bingey rampage.

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Once common in the east and west coasts of the Atlantic, and found as far north as Davis Strait and Cape Cod to the south, they’re now classified as a ‘species of concern’ thanks to overfishing. They aren’t super active fish, nor very good swimmers, so they prefer to spend most of their time resting on the sea floor or holed up in well-protected nooks or small caves under large boulders. Except when spawning, they're found at depths of up to 360 m below the surface. This far down, the ocean can hit temperatures of -1°C, so they're equipped with antifreeze to keep their blood flowing properly.

In their holes, Atlantic wolffish will either live alone or with a mate. The males typically take on the parenting duties, protecting their loose, globular clusters of eggs inside their caves. These egg masses can grow to a sizeable 14 cm in diameter, and the males will wrap their bodies around them as guards while the females wander off or hold the fort from afar.

But this isn’t always the case - in 1982, Gunnar Jonsson from the Marine Research Institute in Reykjavik, Iceland, observed the Atlantic wolffish living in the Vestmannaeyjar Aquarium and found that it was the females that were protecting their eggs, and often from other female wolffish. But all bets were off if the egg mass was damaged, say from the nip of a rival female. When this happened, Jonsson watched as the mother joined her attackers in really unceremoniously devouring the entire egg mass. This mothering behaviour from the females hasn’t been observed in the wild, though, so it could be the product of captive weirdness.

While Atlantic wolffish are described as generally pretty shy, their relative, the wolf eel (Anarrhichthys ocellatus), has a reputation for being pretty friendly, and can be tamed by scuba divers - so long as they have a sea urchin or two in tow. These northern Pacific monsters can stretch to more than 200 cm long, and apparently their flesh is sweet and delicious.

Sources:

Keats, D. W. (1985-11--1) Reproduction and egg guarding by Atlantic wolffish (Anarhichas lupus: Anarhichidae) and ocean pout (Macrozoarces americanus: Zoarcidae) in Newfoundland waters. , Canadian Journal of Zoology 63(11), 2565-2568.