Bluefin tuna is the largest member of the Scombridae Family (tunas, albacores, bonitos, mackerels) can grow up to 9 feet long (3 meters). 4-6 feet of this tuna are more common.
It is the classic ingredient for sushi today. Maguro has a sweet seaweed like taste.
At the market look for fillets that are lighter in color near the surface, juice running in the package, or light grey in color. These indicate that the fillet is not fresh.
Beware of packages with precut slices. Ask the butcher for a fresh cut. Japanese markets understand the fresh cuts for sushi concept and the packaged slices should be fine. It's where the pictures below come from.
Oho Toro- The cuts of meat are divided as belly which is most sought after and very highly prized because of its high fat content and where ohtoro comes from. I've always heard this melts in your mouth. After trying this in Tsukiji Japan. It's the only way to describe this superb cut.
Chu Toro -The back is where chu toro comes from and is the next prized cut. Very good and still can be expensive but worth it.
Akami -Next, the tail is where the darkest meat, Akami, is from. This is typically sold as "regular" cut of maguro. Is readily abundant look for dark red color.
Substitutes include big eye tuna, albacore, yellow fin.