Jacks are pretty brutal. If you're thinking of putting anything in there with him, i'd be getting something bigger and well able to defend itself if he tries it on. If you do introduce new fish, catch him and take him out, rearrange the tank and put the new fish in and then add him in at the end- leave the lights off and let them settle. Good luck!
QUOTE (mosl1 @ Feb 21 2010, 09:30 PM)

Hi
I have a 15cm Mangrove jack in a 4x2 tank, just want to know what is the best tank mate for him. What is everyones thoughts?
Cheers