They have see-through skulls, transparent blood, and they built 60 million nests beneath the frigid waters of the Antarctic Sea. They’re Jonah’s icefish, and a polar research team has just discovered what might be their largest breeding colony in the world.

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An undersea icefish colony.

Scientists from the Alfred Wegener Institute in Germany were cruising the Antarctic Sea last year on the RV Polarstern with a mission to study ocean currents. They were surveying the seabed below the ship, dragging a camera system the size of a car to transmit photos to the deck, when they discovered the nests. 

Related: New study sheds light on Antarctic sea ice mystery

“We just saw fish nest after fish nest for the whole four hours, and during that time we covered maybe six kilometers (3.7 miles) of the sea floor,” said Autun Purser, a postdoctoral researcher at the Alfred Wegener Institute in Bremerhaven, Germany, as reported by CNN. “I’d never seen anything like it in 15 years of being an ocean scientist. After that dive, we emailed the experts on shore who know about fish like this. They said, yep, this is pretty unique.” Purser is the lead author of a study on the icefish colony published last week in Current Biology.

Icefish adapted to water temperatures as low as 0 degrees Celsius by evolving an anti-freeze protein in their blood that prevents the growth of ice crystals. An average icefish nest contains about 1,500 to 2,000 eggs and is guarded by an adult icefish. Scientists suspect these guards are male, but they admit they still have a lot to learn about these unusual creatures.

But just because the ginormous icefish colony surprised scientists, it doesn’t mean nobody knew it was there. Weddell seals, chubby carnivores who can dive down to depths of 2,000 feet, gave the nesting area five stars on the marine mammal review site Kelp, as well as naming it the top attraction on FlipperAdvisor. Scientists’ satellite tracking data confirms that the icefish nesting site is a major draw for Weddell seals.

Via HuffPost, CNN

Images © Purser et al., doi: 10.1016/j.cub.2021.12.022.