Crocodile icefish

Crocodile icefish, or white-blooded fish, are a family of fish (Channichthyidae) in the Southern Ocean around Antarctica. They are pale and ghost-like, with a long flat snout that looks like a crocodile's. At least 16 species are recognised. They are sometimes called ghost fish.

Their big secret is their blood. As adults they have no haemoglobin, the red protein that carries oxygen in most animals, so their blood is colourless. They are the only known vertebrates (animals with backbones) like this. They live in cold water between -1.8 and 2 degrees Celsius, and most are 25 to 50 centimetres long.

A fish that waits

Icefish are thought to be ambush predators that eat other fish, and sometimes krill. Because they wait for prey, they can go a long time between meals, and they can swallow fish up to half their own length. They live mostly on the Antarctic continental shelf and in the Atlantic and Indian sectors of the Southern Ocean. One species, Champsocephalus esox, even lives north of the Antarctic Polar Front.

The Weddell Sea nursery

In February 2021, scientists found a breeding colony of the icefish Neopagetopsis ionah on the bottom of the Weddell Sea. It had an estimated 60 million active nests over about 92 square miles. Most nests held one adult guarding an average of 1,735 eggs. Traces of haemoglobin genes still remain in the icefish genome, even though the working protein has been lost.

On the globe

The model swims in the icy waters near Antarctica. Look for the pale body and the long, flat snout.