It depends on what size tank you put them in.I have a single GT in a 55,he's about 9 inches,and it just look like there is not enough room to keep anything else with him to me.He swims all over the tank.So he lives alone.
HrHagel;3573677; said:Rofl.
A 40g will do fine, for a VERY long time. a 55g they could live healthy and happily for life.

cichlid2006;3573814; said:so your saying that 2 known tank aggressors can live happily in a 3ft tank??
thats terrible advice. a 55g may start to look small for a male GT once it starts hitting 8"+ (my midas is starting to make my 4ft tank look small at 8.5"), and your saying they will be ok when they are 10" long and most likely aggressive as adults.
the 4ft (55g) would be pushing it if they are both male and will likely become too small leading to fights and possibly a death, but as mentioned 5ft+ would be better. of course this paragraph is just my opinion.