the 2 convicts are about 4-5" the tank is 300 gal. shared with other fish of course. i'm just worried about dempseys ganging up and bullying the convicts. other fish can handle themselves if they were to be picked on. athe moment only have 1 jack 3-4" in seperate tank. getting 3 more, not sure on size yet. 1 convict is new and not yet developed into a pair with other one. she has been paired with a dominant 7" parrot.