Well I have a large datnoid that's 12" in with my 11" arowana, and I dropped in a female 5" Jack Dempsey that is doing fine so far! I'll watch um closel! But it's a large 330 gallon tank so they are fine for the moment! I'll throw in a pair of Oscars and see how they do I was also thinking some catfish to help clean the bottom and help me maintain the bottom food everyone else eats at the top sp