ahi tuna
Also known as: sushi-grade tuna, sashimi-grade tuna
A deep-red, meaty tuna (yellowfin or bigeye, both marketed as "ahi") with a mild, clean flavor, most often eaten raw or barely seared -- for poke, tartare, sashimi, or a rare-seared steak. Its firm, dense texture and low fat content keep it from flaking apart when diced small, which is part of why it works well raw.
Buying guidance
When it's going to be eaten raw, this is the one ingredient in a dish not worth compromising on: buy tuna specifically labeled "sushi-grade" or "sashimi-grade" from a fishmonger or counter you trust, ideally the same day it will be eaten. That label isn't a strict legal standard, but it signals the seller is treating it as raw-eating fish -- handled and stored at colder temperatures, and in the US, typically previously frozen solid enough to kill parasites, which the FDA requires for fish served raw. A deep, uniform red color and a clean ocean smell (never "fishy") are good signs; any dull, grayish, or off-smelling piece isn't safe to eat raw regardless of the label.
Substitutions
- Sushi-grade salmon -- softer texture and a fattier, richer flavor; works the same way diced for tartare or poke.
- Cooked tuna or another cooked fish -- loses the specific raw texture and clean flavor a raw preparation is built around, but sidesteps needing raw-grade fish at all.
- Firm tofu, diced small -- a non-fish option that holds its shape the same way in a stacked or molded presentation, though it won't taste like tuna.
Tips & common mistakes
Letting it sit out at room temperature for more than a few minutes lets bacteria multiply fast on a piece of fish meant to be eaten raw -- keep it refrigerated until the moment it's diced and mixed, and serve right away rather than letting a finished raw dish sit out.
Storage
Keep it as cold as possible right up until use -- ideally nested in a bowl of ice in the fridge -- and use raw-grade tuna the same day it's bought. Freezing (many sushi-grade fillets are sold already flash-frozen) is what makes it safe to eat raw in the first place, but once thawed, treat it like any other highly perishable raw seafood and don't refreeze it.