I had my mangrove jack up until about 45cm..... and when they get thise size they are VERY VERY difficult to keep.
They are prone to illness and also as they mature preferre a more brackish water setup.
Mine ended up dieing of unknown reasons just got sick.... there ws no ammonia, nitrates, nitrites or anything.... i blame lack of salt in the water could have been an issue?
But yeh... just so you guys know what your in for... he broke about 10 lids and was going through 4kg of coral prawns a fortnight and a 1kg of whitebait
woah thats alot of food bud!!!!
my togas and other big fish dont even go through that much, not even my old clown trigger!
yeah i agree with your idea of not being in salt water.
when i used to work at Pet Magic (Cannington) we had a larger one (35cm or so) in fresh water and appered stressed out, put him in a marine tank with the salinity around 1.020 (kept it lower to reduce marine disease such as ick etc) and he came right back.
From memory he was an awesome orangy colour and sold him for about $80 i think (close to 2.5-3 years ago now though)