Tuna Fillet

The tuna family (Thunnini tribe) encompasses several commercially important species, each with distinct characteristics. Bluefin tuna (Atlantic, Pacific, and Southern) is the undisputed king—massive fish reaching up to around 680 kg with intensely marbled, ruby-red flesh and a buttery, umami-rich flavor; its fatty belly (toro) commands astronomical prices in Japan. Yellowfin (ahi) is the versatile workhorse of the tuna world—firm-fleshed, deep red, with a clean, mild flavor ideal for searing or raw preparations. Bigeye tuna falls between bluefin and yellowfin in fat content and flavor intensity, prized for sashimi. Albacore, the "white meat" tuna, has the palest flesh and mildest flavor—popular for canning but also excellent seared. Skipjack, the smallest commercial species, is primarily used for canned tuna and dried bonito flakes (katsuobushi). Tuna is graded informally by the trade on freshness, colour, fat and texture: the best fish is sold for raw preparations, lesser grades for cooking, and the rest goes for processing.

Tuna's culinary journey spans millennia and continents. The Phoenicians, those master seafarers of antiquity, are credited with introducing bluefin tuna fishing to the Mediterranean around 3,000 years ago, establishing the almadrabas (trap-net systems) that still operate along Spanish and Italian coasts today. Ancient Romans prized the fish, salting and trading it across their empire. In Japan, tuna's story takes a surprising twist: for centuries it was considered "gezakana"—inferior fish—because its red flesh spoiled quickly. Lean tuna entered Edo sushi in the 19th century, usually marinated in soy sauce (zuke) to keep it. The fatty belly (toro), however, was often discarded until the 20th century. Refrigeration began to change perceptions, but it was only after World War II, as Western dietary influences gave the Japanese a taste for fattier meat, that toro rose to gastronomic stardom. Today, Japan remains the largest market for sashimi tuna, and in 2019 a single bluefin sold for a record 333.6 million yen (about €2.7 million) at the New Year auction at Tokyo's Toyosu market.

Tuna's remarkable flesh owes its character to the fish's extraordinary physiology. As one of the few partially warm-blooded (regionally endothermic) fish, tuna maintain elevated body temperatures that power their ceaseless swimming—some species never stop moving their entire lives. This metabolic furnace demands abundant oxygen, supplied by exceptionally high concentrations of myoglobin, the iron-rich protein that stores oxygen in muscle tissue and gives tuna its characteristic deep red color. When exposed to air, myoglobin oxidizes, shifting from vibrant red to brown—a process some distributors counteract with carbon monoxide treatment, which binds to myoglobin and locks in a deceptively fresh-looking cherry hue. Temperature control is paramount with tuna: the fish's muscle tissue contains high levels of free histidine, an amino acid that bacteria convert to histamine when the fish is improperly chilled. Elevated histamine causes scombroid poisoning, a rapid-onset food intoxication with allergy-like symptoms. Critically, histamine is heat-stable—cooking, freezing, and smoking cannot destroy it—making proper cold-chain management from boat to plate the only defense. The Japanese practice of super-freezing tuna at -60°C not only halts histamine-forming bacteria but also prevents the oxidative browning that degrades both appearance and flavor.

Tuna sustainability presents a complex, species-dependent picture. Atlantic bluefin populations were severely depleted by decades of overfishing driven largely by Japanese sashimi demand. Under strict ICCAT quotas since 2007, the eastern Atlantic and Mediterranean stock has recovered strongly, and in 2021 the IUCN reclassified Atlantic bluefin from Endangered to Least Concern. The smaller western Atlantic stock remains weaker. Pacific bluefin, still heavily fished, is listed as Near Threatened and recovering under quotas. Conversely, skipjack and many yellowfin stocks are generally healthy when caught using pole-and-line or troll methods. The fishing method matters enormously: purse seining with fish aggregating devices (FADs) results in significant bycatch of juvenile tuna, sharks, and sea turtles, while pole-and-line fishing—traditional in the Maldives and parts of Indonesia—is highly selective and supports coastal communities. Look for Marine Stewardship Council (MSC) certification or consult a European seafood guide such as WWF's. Traceability is key: avoid tuna products lacking sourcing information, as these may originate from illegal, unreported, and unregulated (IUU) fisheries associated with human rights abuses.