Tuna has come a long way since food writer James Beard said it was a fish best eaten canned, rather than fresh. Thanks to the influence of Japanese cuisine, fresh tuna has become popular.
What is it? There are many varieties of this fish but at supermarkets, it is usually just labelled 'tuna', without specifying the variety. The most popular types are yellowtail (also known as hamachi), bluefin (the type most prized by sushi chefs), bonito (frequently dried) and albacore (which you'll most often see canned, rather than fresh, except at Japanese restaurants).
How is it available? Fresh, frozen, canned and dried. The most expensive 'canned' tunas come from Spain, Italy and France and are usually in jars, rather than cans. Many connoisseurs consider these the best, but if you're used to milder-tasting tuna canned in water, you might dislike these rich, fattier versions. Dried bonito - katsuo-bushi in Japanese - is one of the main ingredients in dashi broth (the other is kombu, or dried sea kelp).
What else? Toro is the general term used for tuna belly, but there are several different grades based on how fatty it is. The pale pink o-toro is the fattiest, best and most expensive.
How to use: when fresh tuna is overcooked, it can be hard and dry. Modern chefs usually prefer to serve it rare or raw (see recipes, left). For tuna tartare (above), mince top-quality raw tuna and mix it with soy sauce, sesame oil, minced spring onions and some wasabi paste to taste.
For tuna canned in water, there's the classic tuna sandwich (break the fish into flakes and mix with mayonnaise, celery and chopped gherkins). If you're using tuna in olive oil, though, mixing it with more fat (the mayonnaise) is overkill and it doesn't really let the fish flavour come through. Instead, drain the tuna and reserve the oil. Take a good-quality, crusty loaf of bread, cut it in half lengthwise and pull out some of the soft crumb to leave a hollow. Mix the tuna oil with red-wine vinegar and spoon some into the lower half of the bread. Add the tuna, slices of ripe tomato and thin rings of red onion then sprinkle with salt and freshly ground black pepper. Spoon some of the vinaigrette over the cut part of the top of the loaf and press it firmly over the filling. Wrap the loaf with plastic wrap and weigh it down with a cutting board. Refrigerate for about an hour then slice and serve.