As far as canning vs freezing and general processing goes…
My method has been to:
trim bloodline off loins and save for crab bait and/or cat food.
Trim off the thin side of the loin that has the sinew/muscle fibers.
Trim off the last 3-4 inches of the tail of the loin, which also contains a lot of the tough fibrous tissue.
All of the trim (minus the bloodline) goes to the canner.
All of the quality loin meat (which is the majority) gets portioned out and vac packed for the freezer.
The amount of canned tuna you get, just from the trimmed tough bits, is more than adequate for me, and a better use for this quality of meat IMO. The frozen loins are then only the best quality meat, perfect for poke bowls, sashimi, seared/grilled etc. No tough/chewy bits involved. It works for me, YMMV.
