Notothen, commonly known as icefish, is a family of fish found primarily in the cold waters of the Southern Ocean surrounding Antarctica. They are unique for their lack of hemoglobin, which gives their blood a clear appearance. This adaptation allows them to thrive in oxygen-rich, frigid environments. These fish are an important part of the Antarctic ecosystem, serving as prey for larger species such as seals and penguins. Notothen are also notable for their ability to survive in extreme temperatures, making them a subject of interest for scientific research related to climate change and marine biology.