"Is it real tuna?"
Or is it 'escolar'http://en.wikipedia.org/wiki/Escolar
I have to say this makes me uneasy. We buy 'whole chunk white albacore' tuna in cans in the belief that if we can actually see the texture of a chunk of fish it must be OK. Are we eating escolar?
Aside from this being yet another of numerous posts already on this topic, the issue is fresh fish, where the substituted fish are substantially cheaper than the fish they're replacing. Albacore tuna that gets into cans is a relatively inexpensive fish, so even if the canner was that brazen, there's no money in it.