Japan — bluefin tuna fishing from ancient Japan; Tsukiji and now Toyosu market in Tokyo as the world center of bluefin tuna trade; the specific anatomy-based value system formalised in Edo period sushi culture and refined through the 20th century
Bluefin tuna (hon-maguro, Thunnus thynnus or T. orientalis) is organised into a precise value and flavour hierarchy based on anatomy — the most sophisticated single-ingredient classification system in Japanese seafood culture. The core divisions: akami (red meat, the leanest portions from the upper back and tail — clean, iron-rich flavour with minimal fat); chutoro (medium fatty — from mid-belly and back near the head — balanced fat and lean character, considered by many the most complex); otoro (fatty — from the front belly section — extremely high intramuscular fat, the most prized and expensive, known for its 'melting' character); and kama (collar/neck area — extremely fatty, usually grilled, not used for sashimi). Sub-categories: naka-toro is the middle belly region between chutoro and otoro; toro with shimofuri (fat marbling visible as white streaks) commands the highest premiums.
The premium hierarchy (akami < chutoro < otoro) reflects a modern preference for fat — historically, akami was prized and otoro was discarded or fed to cats (it was considered too fatty). This reversal happened during the post-WWII economic boom as refrigeration allowed tuna to be transported and consumed fresh rather than fermented (zuke marinated). The different flavour profiles require different preparations: akami — zuke (soy marinade) or sashimi; chutoro — ideal for sashimi; otoro — best as sashimi or very briefly seared. Temperature at service affects experience: slightly warmer than refrigerator temperature allows fat to partially melt on the palate.
At the highest-end sushi counters, the itamae will specifically point out the different parts of tuna they've prepared that day from the whole fish — this is an educational opportunity for the diner. Pacific bluefin (Thunnus orientalis, 'hon-maguro') from Japan and Atlantic bluefin (Thunnus thynnus) have different fat profiles — Pacific tends toward richer, fattier flesh; Atlantic can have more complex, leaner characteristics. Boston bluefin in winter and Mediterranean bluefin in summer are the premier Atlantic specimens.
Assuming otoro is categorically superior to akami — the preference depends on the dish and the diner; akami's clean iron flavour is often preferred by experienced sushi eaters for the majority of a meal. Serving tuna too cold from the refrigerator — the fat in chutoro and otoro requires some warmth to become expressive. Ignoring the value of kamatoro (collar meat) — it is among the fattiest parts of the fish but often overlooked because it is presented grilled rather than raw.
Tsuji, Shizuo — Japanese Cooking: A Simple Art; Davidson, Alan — The Oxford Companion to Food; Tsukiji market documentation