Bluefin Tuna

Bluefin tuna is the largest of the tunas: over three metres and four hundred kilos, capable of seventy kilometres an hour, and warm-blooded in a way almost no other fish is. That physiology is why the flesh is dark red and dense with myoglobin rather than pale like other tuna.

Every spring the adults enter the Mediterranean from the Atlantic to spawn, passing Sicily, Sardinia and Calabria in May and June. Every trap fishery in southern Italy was built on that migration, some of them documented since the thirteenth century.

The flesh changes so completely from one part of the fish to another that each has its own name, price and cooking. Ventresca is the fatty belly, tarantello the flank, buzzonaglia the dark meat near the bone, filetto the lean loin. Then there are the cured parts: bottarga from the roe, lattume from the milt, mosciame from the air-dried loin.

One thing that matters at the supermarket: canned tuna is almost never bluefin. It is skipjack or yellowfin, different species, far more abundant and far cheaper.

Closer to beef than to any other fish. The lean loin is clean, faintly metallic in the way rare steak is, firm enough to hold its shape under a knife and with none of the oily aftertaste of mackerel or the blandness of canned tuna.

Ventresca is a different food entirely: heavily marbled with white fat that melts at body temperature, buttery, with a sweetness that lingers. This is the cut sold in Japan as otoro, and the reason a single fish can be worth thousands.

Buzzonaglia, the dark meat along the backbone, tastes strongly of iron and sea and is the part most people would call fishy. Sicilians turn it into meatballs and ragu.

Overcooked, all of it turns dry and chalky within seconds: the failure mode is exactly that of a well-done steak, and just as irreversible.

Short cooking or none. A loin steak wants thirty seconds a side in a very hot dry pan, leaving the centre raw. Anything beyond that and it goes dry and chalky, exactly like an overcooked steak.

For raw dishes, slice against the grain with a long knife in one clean pull, about half a centimetre thick. Tartare needs only olive oil, salt, lemon and perhaps a little shallot. In Sicily it is also served marinated in oil and oregano, or as carpaccio with citrus.

Traditional Sicilian cooking, though, cooks tuna hard and long: alla stemperata with celery, olives, capers, vinegar and sugar; alla marinara with tomato and onion; as meatballs from the dark buzzonaglia. Ventresca handles slow braising because the fat protects it.

Grate bottarga di tonno over spaghetti dressed only with oil and garlic, or slice it thin onto buttered bread.

Safety note for raw tuna at home: EU rules require freezing at -20C for at least 24 hours before raw consumption. A domestic freezer needs about 96 hours to achieve the same result.

Fresh tuna changes faster than almost any other fish. Wrapped in paper, covered, on the coldest shelf at 0 to 2 C, the working window is twenty-four hours and at the outside forty-eight. What happens across it is visible: the myoglobin at the surface oxidises and the cherry red walks inward to brown, the flesh slackens and loses its shine, and a cloudy liquid gathers in the dish. Beyond that, the date on the label and the fishmonger are the people to ask.

For anything served raw, EU rules put the freezing step on the seller, at minus 20 C for at least twenty-four hours right through the piece, so ask the counter whether it has been frozen; at home a three-star freezer at minus 18 C is usually given ninety-six hours instead. Thawed slowly in the fridge, a properly frozen piece loses very little liquid. A sealed jar of tuna in oil runs to its date, two or three years out; once open it goes in the fridge with the fish kept under the oil, and any piece standing above the oil line dries and darkens within a day.

At the counter the colour is dark cherry red, not pink and not fuchsia. A very bright, perfectly even red is often the mark of carbon monoxide treatment, permitted in some countries and banned in the European Union, which locks the colour in place for days regardless of what the fish is doing underneath. The steak should look glossy and firm with no reddish liquid pooling in the tray, and the grain should be visible: muscle bundles separated by thin white lines of fat, at their most dramatic in the belly cut, the ventresca.

Every legally caught bluefin travels with a Bluefin Catch Document, the BCD, which follows the fish from the boat to the counter; a serious fishmonger knows what that is and can tell you where the fish came from. The usual substitution is yellowfin sold under the bluefin name: paler, far less marbled and roughly a third cheaper, and in American shops both it and bigeye go by ahi. On tins and jars, read the species: Thunnus thynnus is bluefin, Thunnus albacares yellowfin, Katsuwonus pelamis skipjack.

In the US, sashimi-grade bluefin is a special-order item from fishmongers and online suppliers such as Catalina Offshore Products and Browne Trading; much of it is Pacific bluefin or ranched Atlantic. Expect roughly 25 to 60 dollars per pound for loin and 40 to 90 for belly. Italian preserved tuna, bottarga di tonno and mosciame come through Gustiamo, Eataly and Sardinian importers.

In the UK, specialist fishmongers and The Fish Society list bluefin loin at roughly 60 to 120 pounds per kilo when available; jarred Sicilian and Sardinian tuna in olive oil is far easier to find, at 60 to 110 pounds per kilo drained.

Ask two questions. First, the species: "tuna" on a label covers three or four completely different fish, and yellowfin is routinely sold as the real thing. Second, the catch documentation: every legal bluefin carries a Bluefin Catch Document that follows it from vessel to counter, and a serious supplier knows exactly what you are asking about.

On colour: an unnaturally bright, even red often means carbon monoxide treatment, legal in some countries and banned in the EU, which fixes the colour of fish that is no longer fresh. Real bluefin is dark cherry red and dulls with age.

Favignana, in the Egadi islands off Trapani, is where the industry lived. The former Florio plant is now a museum with the original equipment, and although the trap no longer operates, the island's restaurants and conserve makers work good fish.

Carloforte, on the Sardinian island of San Pietro, has the only working Italian trap and a cuisine of its own, since the Tabarkino community came from Liguria via Tabarka in Tunisia and still speaks a Genoese dialect. The Girotonno festival at the end of May is four days built entirely around the fish.

The Trapani coast (San Vito Lo Capo, Bonagia, Scopello) keeps the buildings of the disused tonnare and a living tradition of tuna cooking, and Marzamemi in south-east Sicily has turned its old tonnara into a small square of seafront restaurants.

Go between May and July, when the fish passes and the quota is landed. Outside that window you are eating frozen or ranched tuna: fine, but worth knowing.