Ahi refers to yellowfin tuna (Thunnus albacares). Seafood lovers are drawn to this warm-water tuna for its Epicurean virtues, including a mild, meaty flavor. The highest grade Tuna has a higher fat content, develops a deeper red color thatcommands a higher price and is great for sashimi and other raw preparations. Tuna is graded for fat content and color as well as freshness.