In your cooler you might find two different looking pieces of fish. They are both bluefin tuna. They come from different parts of the same fish. The belly portions, or "Toro" in Japanese, contain much of the desired belly fat and have been preserved skin on. The other portion you might find is a "Darne de thon" or Tuna Steak. A "darne" is a thick section cut from a substantial fish, such as salmon or tuna. The word is French, but it comes originally from Breton darn, which means ‘piece’. The darnes have been preserved skinless. Both cuts are sushi grade and have been preserved and treated in accordance with best practices.