Negitoro

Negitoro (ネギトロ) is a Japanese cuisine of minced raw tuna scrape, the fatty parts of the fish that cannot be made into other meals, commonly served together with green onion. In addition to being an ingredient to sushi of various types, they are used as a rice bowl topping, forming negitorodon.

Etymology
Multiple hypotheses exist.

Combination of green onion and toro part of tuna
Negitoro is so named because it is a combination of green onion (ネギ), and toro (tuna) (トロ, fatty parts of tuna).Since the 1980s, with the appearance of new toro sushi combined with pungent vegetables, the well-matched taste and combination of toro, green onion and nori seaweed have become popular.

Toro referring to something other than part of tuna
One of the restaurants hypothesized as the origin of the dish claims the dish was so named based on mugitoro, a dish that was popular around the place at the time.

Negi referring to something other than green onion
In the field of construction in Japan, digging soil from the ground to constructing building is termed negiru (根切る), and it was hypothesized that the term adopted into negiru (ねぎる) or negitoru (ねぎ取る) to refer to meat being scraped. Tuna fishing groups support the hypothesis. However, dictionary editors question the hypothesis, claiming there is no verifiable usage of the verb form of the adopted word negitoru (ねぎ取る), and thus the hypothesis cannot be sustained. It has been suggested the negitoru origin hypothesis emerged after the 2000s, and until the 1990s the mainstream hypothesis on the origin of the negitoro dish was that the term is a combination of green onion (ネギ) and toro (sushi) (トロ).

Mass-market product
Negitoro sold to the mass market and distributed into retail channels like supermarkets is mass-produced in fish factories. They use lean meat of various fishes, including, for example, yellowfin tuna, marlin, bigeye tuna, and albacore, then adding additives like vegetable oil, shortening, lard, antioxidants, and condiments. Dedicated fat products for the purpose of negitoro manufacturing have also been produced.

Japanese consumer groups and magazines have raised concerns about such practices being possibly misleading and raising potential health concerns. However, there are also claims that unprocessed tuna scrape is not popular.