well in my150us i have a parachanna obscura/channa pleuro/with a male krib,seven months now all's still fine and dandy,
also in another tank i have three 0.5-1inch dwarf puffer's with a 13inch reed fish and one has become best buddys with the reed fish going around all day with him
I had 2 glass cats that tried to school with a shoal of barbs once.
Don't have it anymore, but I had a 8" oscar that grew up with a 0.5" Jag (when I got him.) The jag is still there, but the oscar jumped out of the tank at 10"
Years ago read up about a guy who had a Red Snakehead with a Labidchromis Caerelus as mates. The amazing thing was the Sankehead ate or killed anything he put in except the African cichlid!!