BIIIIIG TANK BIIIIG BIIIIG TANK. I think its sad that carapos haven't yet reached 2 foot in captivity, If I had the money I would get one, but youd need at least a 300 gallon to take care of it right. Also, I think its important to note that they spend half their time in open water and half in shallow swamps, wherein they make nests. I have read many a scientific paper on this, look them up on goole scholar.
If I ever got a carapo knife, It would be in a tank at least 6 foot by 12 foot, with half the tank being 1.5-2 foot deep, elevated, and the rest at least 4 foot.
This is the consensus I have come to after research, I really wanted one until I found out about their life cycle. I think it's mean to force a wild caught fish into a tank without considering its natural cycles. They also need a rainy season, though that can be accomplished with a TDS/conductivity tester and D/I or R/O water.