I have been to 99 Ranch they are brutal on there live fish tanks with bass and catfish. I will probably head over there I usually find some cool frozen fish.
As long as you're supplementing with vitachem or pellets thiaminaise isn't an issue. I think the lipid profile of tuna would be more of a concern given you're supplementing with b-1 already.
My army usually take yellow croaker and gourami along with sardine. Tried to feed it ompok and red snapper but tosses it aside after holding it in it's teeth for a minute. Can't tell whether it's feeling it with it's tongue to decide to swallow it or not.