What is Saku Tuna?

Answer 1

The best answer I've found so far, was from when I worked in restaurants. The sushi we served was always fresh, real, and caught by local fisherman from around the world. Alas, all sushi is not made the same, I was told that the "block" sushi I saw at lower grade sushi establishments was made from the loose bits of tuna that are pasturized and molded into blocks. By the looks of it, this is what I suppose saku tuna is

Edit: As far as I know Saku Tuna is yellowfined tuna that is labeled with Maguro, most often only used for labeling bluefin tuna. So you can call the tuna Maguro Tuna-Saku. I suppose it is a way to sell the cheaper yellowfin tuna to a higher price.