Sushi Bar Fish is a term used to describe the type of fish used in sushi bars. The three most common types of fish used are EEL (3 letters), TUNA (4 letters) and Ahi (3 letters). EEL is a long, snake-like fish that is often served grilled or fried. TUNA is a large, predatory fish that is usually served raw. Ahi is a yellowfin TUNA that is also served raw. All three types of fish are popular ingredients in sushi dishes.