Gar aren't aggressive, barring the alligator in general. they aren't territorial like cichlids... they will however eat anything that can fit in their mouthes or is silver( they hold great hate for silver arrowana in particular ime) some fish bend or break this general rule. But most do not. Cichlids work until the fish decide to start breeding or dont want the gar in their territory any longer, the gar don't really "fight back" and will cower in a corner until they get spooked badly enough they jump out of the tank or break their backs. atm I keep a CK, and some Spiney eels with my gar and this has worked going on year 3. the CK has only been in the tank about 6 monthes now? maybe less and has only recently been bitten by my Cuban. Since then things have been fine, both went for the same chunk of worm.