we once had a jurapari (sp?) with 2 - 18" aros...lives peacefully for about 10 years or so and then the jurapari could not be found...the aros didnt have any unsightly bulges and the jurapari was always cautious when swimming from one side of the tank to the other...i remember that he would swim sideways at times to keep an eye on the bruisers above.
I have some weird mixes as well
one tank converting to brackish has 2 gsp with a bunch of feeder guppy
other tank = fire eel, rope fish, leaf fish, corys, kribensis