The northern bluefin tuna (Thunnus thynnus), or giant bluefin tuna, is a species of tuna native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea and the Black Sea. 

The northern bluefin tuna is an important commercial species, especially for sushi and sashimi.  This commercial importance has led to significant ranching of the fish throughout the Mediterranean ocean.   This fish provides the finest sushi topping there is available in the world, but in order to fetch the best price, the fish must be in optimal condition.  In order to optimize the condition of the fish, Atlantis Group HF runs a tuna ranch in Croatia, Kali Tuna D.o.o., which is recognized for the best ranched tuna in the world. In addition to its ranching operations in Croatia, Atlantis Group HF also handles Northern Bluefin tuna from Canada and Mexico.

The body of a fat Northern Bluefin Tuna should look like an American football.  A slim back portion indicates low fat contents.  The head is conical and the mouth rather large. Northern bluefin tuna can live for 30 years. 

There is also a Pacific Ocean variety of the Bluefin tuna, that specie is now commercially cultivated off the Japanese coast