I have a breeding pair of jags in a 125 gallon tank. They are with, all mature, breeding pair of convicts, an oscar, jack dempsey, severum, featherfin catfish, and huge pleco...to clean up the eggs before they hatch. The only reason this works with a breeding pair is the fact that the dominant fish in the tank is the oscar. Jags can have a nasty reputation, but its mostly because people put them in small tanks. Anything over 100 gallons will provide plenty of swimming room and floor space to establish territory. Make sure you buy the other tank mates soon, so they have a chance to grow up together. Adding tankmates when the jags are full grown will prove to be much more difficult. Just to note, the male jag fights with the dempsey over territory on occasion. The other fish are pretty much ignored .