A 'Lean' cut of Maguro from the backside of the Tuna, not a fish specifically; (Related: Maguro, Chutoro, Otoro, Toro)
THE FACTS: In Sushi, Akami refers to any ‘Lean Cut’ of Maguro (Bluefin Tuna) and is not a specific species of fish. Given the relative popularity of Maguro in the world of Sushi culture and the rather immense size of a single fish, the need for classifications of the various cuts was born. By analogy, Akami is to Maguro what the Sirloin Tip is to Beef.
With Bluefin Tuna, the cross-sectional quartered slabs are referred to in Japanese as the Cho. When viewed from the side, a single Cho yields 4 different basic cuts: Chiai (Blood saturated portion that is typically discarded and cannot be eaten), Akami (Lean red meat portion), Chutoro (Moderately fatty portion), and Otoro (Fattiest and highly desired portion). For reference, a lesser known 5th cut called Shimofuri also exists and is highly desirable and worth trying when available.
In almost every Sushi-ya, when ordering Maguro from the menu, the Akami cut is what will be served. Akami should be a nice deep shade of red, and is marked for having a soft texture and clean, simple taste that isn’t nearly as fishy by comparison; which accounts largely for its defacto popularity among all ranks of Sushi enthusiasts. Moreover, Akami is an excellent source of nutrition that is rich in Iron, DHA and EPA.
In terms of actual grades, Akami is by far the most plentiful portion of Maguro available and is priced accordingly at the lower end of the Spectrum. Further, as Honmaguro (True Bluefin Tuna) is not always available, be careful of potential substitutions for the lesser quality Kihada (Yellowfin Tuna) or Mebachi (Big-Eye Tuna), both of which are even less expensive by comparison.
Depending on the variety of Tuna being offered through substitutions, Maguro essentially has become a year-round Sushi selection as the Bluefin and Big-Eye Tuna varieties are best through the Summer and Autumn months and Yellowfin Tuna reaches its peak from Winter through Spring. With Akami, and all cuts of Maguro for that matter, avoid any meat that has become discolored, gray, or is leaking its moisture, since this is an obvious indication of spoilage.