Sometimes the most exciting discoveries are completely unexpected. That’s what happened when a team of researchers stumbled across a massive colony of nesting icefish in the Antarctic.

In February 2021, a German research vessel went on an expedition in the Weddell Sea to study ocean currents in the Antarctic. They were conducting a survey of the seafloor with a high-resolution camera when they spotted the first nests. Right away, they knew they had found something remarkable.

They shared their results last week in an article for Current Biology, with estimates of approximately 60 million (million!!) active nests in a colony that covered 93 square miles—about twice the size of San Francisco. Each nest had about 1,700 eggs, and most were guarded by an adult icefish. The nests were between 1,300 to 1,700 feet below the surface in the ocean’s twilight zone.

The researchers believe this is the largest continuous fish breeding colony ever discovered. The amount of fish found  is exceptionally high for the mostly-sparse Antarctic seafloor.

Icefish have special adaptation skills that allow them to survive in the frigid waters of the Antarctic. Unlike other fish, icefish lack red blood cells and hemoglobin, two things that help animals transport oxygen. Instead, they have large hearts, big blood vessels and colorless blood that allow them to get all the oxygen they need to survive.

Icefish, like other fish found in the Antarctic, also have special anti-freeze proteins that prevent ice crystals from forming in their blood. This characteristic is critically important, as the water temperature hovers right around freezing.

This groundbreaking discovery not only furthers our knowledge of this fish and their behavior but also reminds us that there is much to discover in the Antarctic and beyond. As the authors of the scientific article state, “This discovery provides support for the establishment of a regional marine protected area in the Southern Ocean.”

Read more about their incredible discovery here. Can’t get enough of cool deep-sea discoveries? Read about weird and wild deep-sea creatures and recently discovered ocean species on our Ocean Conservancy blog.