The successful origin and diversification into 100 species of fish, collectively called notothenioids, is a textbook case of how evolution operates. A period of rapid cooling led to mass extinction of fish acclimated to a warmer Southern Ocean. The acquisition of so-called antifreeze glycoproteins enabled notothenioids to survive in seas with frigid temperatures. As they adapted to vacant ecological niches, new species of notothenioids arose and contributed to the rich biodiversity of marine life found today in the waters of Antarctica.

Notothenioids account for the bulk of the fish diversity and are a major food source for larger predators, including penguins, toothed whales, and seals. Yale's Peabody Museum of Natural History has one of the most important collections of these specimens in the world.