Most cold-tolerant hadal fish

The hadal zone is any point in the ocean that stretches more than 6,000 metres (19,685 feet) below the surface. The coldest water endured by a hadal fish is -0.05 degrees Celsius (31.9 degrees Fahrenheit), as logged in the Atlantic/Southern oceans' South Sandwich Trench by three species of snailfish (Liparidae). The fish were recorded at depths up to 6,640 metres (21,785 feet). The findings were published in the journal Deep-Sea Research Part II in December 2021.

The dives into the South Sandwich Trench took place on 2-10 February 2019, as part of the Five Deeps Expedition, a project to visit the deepest point in all five of Earth's oceans in the cutting-edge reusable submersible DSV Limiting Factor.

Even lower temperatures have been endured by fish living in shallower waters nearer to Antarctica. Members of the icefish family (Channichthyidae) live in waters that can dip to -2°C (28.4°F), made possible by chemicals in their blood that act like anti-freeze.