by Alec61 on Wed Jan 04, 2012 12:04 am
For the most part, a GT won't be overly aggressive... the only fish out of the 3 that could live for life in a 40gal tank would be the dempsey. Just the oscar alone will reach up to or over 14" long...so a 72/75 gal tank just for it would be the way to go.
For the most part, pikes will get too large for a 40gal, same with a texas or black belt..and all 3 would be more aggressive than a green terror (not sure on the pike for aggro behavior).
Going with female fish might be an idea, but it is pretty much impossible to sex an oscar unless you vent it. The dempsey and GT will show some some signs of sex, but not until they are 3-4" long or larger.