I had a similar experience with a red-tail shark and a polypterus. The red-tail was about 4-1/2 inches and the polypterus was only 8" long. I thought for sure the red-tail was too large to fit in the polypterus' mouth and they seemed like tough fish...after the first day I noticed the polypterus seemed to be hunting the red-tail and before I could set up a temporary tank all of a sudden the polypterus looked twice it's normal diameter and the red-tail was gone.