Blackfin tuna (Thunnus atlanticus) is the smallest tuna species in the Thunnus genus, generally growing to a maximum of 100 centimetres (39 in) in length and weighing 21 kg (46 lbs). Blackfin have oval shaped bodies, black backs with a slight yellow on the finlets, and have yellow on the sides of their body. Blackfin are only found in the western Atlantic from Cape Cod to Brazil.
Blackfin hunt both epipelagic (surface) and mesopelagic (deeper water) fish and squid. They also eat crustaceans such as shrimp, crabs, amphipods, stomatopods and the larva of decapods. They are a short-lived, fast-growing species; a 5 year old fish would be considered old. They reach sexual maturity at two years old, and spawn in the open sea during the summer. Blackfin tuna are a warmer-water fish, preferring water temperatures over 20 °C (68 °F). What they lack in size, they make up for in numbers and willingness to bite.
In 2010, unlike other tuna species, Greenpeace International did not add the blackfin tuna to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."