The Patagonian Toothfish (Dissostichus eleginoides) is a large, slender fish found in the cold, temperate waters (from 50 to 3850m) of the Southern Atlantic, Southern Pacific, Indian and Southern Oceans on seamounts and continental shelves around most sub-Antarctic islands. A commercial fishery exists for Patagonian Toothfish; the meat is sold under the trade names Chilean Sea Bass in the USA and mero in Japan, and high prices are paid for it. Illegal overfishing threatens the species as it is slow-growing, reaching maturity between 10 and 12 years of age. The average weight of a commercially caught toothfish is 9 kilograms (20 pounds) with adults reaching a maximum of 113 kilograms (250 pounds). They are thought to live to 50 years, reaching a length of 2 metres (6.5 feet).

Illegal catches may be up to five times the legal catch limit. As a direct result, some researchers have predicted a total collapse of the fishery within two to five years. Called the "white gold of the Southern Oceans," illegal toothfish catches are unloaded at so-called "pirate ports" in countries such as Namibia, Mauritius, South Africa's Prince Edward Islands, and Australia's Heard Island and McDonald Islands. The fish are then sold on the black market, a single sashimi-grade specimen fetching as much as USD $1,000.

Patagonian toothfish feed largely on squid and prawns and, in turn, constitute a large part of the diets of sperm whales and Southern Elephant Seals.