Swai is fine to feed. I normally use tilapia and shrimp as a staple but recently have tried haddock and cod. They have all been eaten without any hesitation, so go for trying any of these.
Salmon is the one thing that all my predators go for the most, but like it was said earlier, it can leave an oily film on the top of the water. Because of this, I always feed salmon on a water change day - never had an issue with doing it this way. I also noticed a lot more growth out of some of my slower growing fish using salmon in the rotation.