Permanent? None.
They will kill everything whether they can fit it in their mouth or not.
Mine are juvies (Aprox 20 cm), and they already killed Geos twice their size.
If you wanna keep tankmates, you can try for a few month, once they reach maturity it's over, though. Only chance would be a fish that can bully them, but then they won't move, and might die of stress, so it's not a solution at all.
Afraid there is no tankmate alternative for any channa other than the rare cases of Pleurophthalmas and Marulius that some people manage to make work.