single tropheus

They generally won't predate other fish...they may well snack on fry size fish.

They are better in a colony as they like social interaction with their own kind. That said I know a number of people who have one or two in with mbuna and have not had problems - these would be where they are kept with very aggressive mbuna which are well able to look after themselves. I don't think you'll find many other tank mates which will be able to survive with them. You would still want a big tank, ideally 55 G plus.
 
Its best to keep them in a setup that will be most comfortable to them. Sort of like stocking tetras or rasboras, they feel best in large colonies. They may not go completely out of control on their own but as coler said a mbuna tank is much different than your suggested stocking. Plus, you're pretty much maxed out for bioload IMHO.
 
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