I've never heard any success stories of them being kept with tankmates, but I don't have any hands-on experience with these guys so don't take my word as final.
I've had luck with my wyckii (14") and tankmates...my jardini (16-17") is in with 2 other arowanas (15") and I have 3 moray eels (3 feet +)in my salt tank. These are all fish that shouldn't be with tankmates (or in the case with the morays; similar species), but if you take extra precautions it
may be a possibility.
I really have to emphasize that 'may'...it's a gamble. I've done specific things for each setup to allow for this compatability, whether it's specific feeding schedules and altered tank decor (like visual barriers and driftwood/rock cluster)
Worst comes to worst, give him a try for a while and if you see him starting to show aggression then sell him...I'm sure there will be someone on MFK willing to pick him up.
Just a side note, in my Baensch Vol. II atlas there is a note in the breeding section of the yarrelli that says ''Who wants to breed this demon, anyway?''
Best of luck...I hope it works out. You'll have to keep this thread updated because I know I'll be looking for updates.
