Dude, they dont get to 5 or 6 feet like that.Especially in captivity. It will be an great achievement if you get the Cachapira , tsn (cachara) x rtc (pirarara) , to reach the 3 ' mark. They get big, but it has a smaller mouth and is less threatning than a pure rtc. They need to be in the wild and be really, really, old to get to the 4 or 5 feet mark. The biggest ones , here in brazil, are in the Panatanal , in a very special fishing spot and they get one 5 footer a year. Is very rare. You will be fine with it in the pond.