i usually try to not post links to other sites but not many people keep this species so i figured it would be welcomed here in this case. You might want to consider contacting this person , theirs are 20 inches so they probably have had them a long time and can give you lots of info on them. I have only seen them before in videos from the wild...
http://aquaticpredators.com/forums/index.php?showtopic=38701
What size tank do you have yours in ? This person has his in a 400 gallon tank because of the extreme size they attain.