mine is approx 12" and in a tank on his own.not because he cant have tankmates,but,thats the way i prefer it.
do not put odoes in with any fish that look simimlar as it will end in tears.my odoe has eaten apollo sharks,clown loaches,tryed to kill a gar after the gar was in the tank for about 10 seconds.odoe tankmates are trial and error really.just be prepared to watch the tank for a few days if you add new tankmates.
any other questions,just ask away.