You might be able to get away with a lemon peel angel in the tank if you scratched the flame angel...that'd give you the yellow fish look you might be seeking.
You can get a reproducing population of pods
in 2 liter bottles, but I've never attempted it.
I've heard rumors of sallys eating small fish, but have never seen such a thing happen and have a hard time believing it. Crabs are opportunistic animals, though I don't believe they are fast enough to catch a healthy fish it is even mentioned on LA's page for them. I just think that is one huge crab and the world's smallest fish.