Which I have read are two of the most aggressive Cichlids.
they are indeed large cichlids, but neither is really too aggressive compared to a lot of the other fish out there like managuense, trimacs, devils, convicts, etc.
I bought them and put them together in a 29 gallon tank with other fish
a 29 gallon is not nearly large enough for either one of those fish alone, nonetheless for both of them. a 55 gallon is really needed for either one alone, a 75 or larger for the both of them.
Is it possible that these fish would always be peaceful together or should I be worried about if I buy more. I bought another Oscar but I'm scared to buy a Jack because the pet stores tell me they will be mean to each other. Does anyone have these two fish together? Are they peaceful with each other?
i have kept them together several times and found that jacks are typically a little more aggressive than the oscars, but also do not grow as large.
if the oscar has a little size advantage on the jack they do very well together in a large enough tank IMO.
cichlid aggression is largely dependent on tank size for available territories.....i.e. a jack in a 29 is going to seem much more aggressive than that same jack in a 55 gallon or larger.
HTH
M