I have an african brown knife. it's a bit smaller than most other knife species but i do know a bit about them. Most knives are very shy, and don't like being around their own type. As a gereral rule of thumb they can eat anything that fits into their mouth (just like most fish). My African brown knife ate all my Neon tetras and its maximum size is only 8". Most knives do get large and prefer live foods, but will acclimate to most other foods including flakes. Mine has been on a flake diet for almost a year. It is also supplemented with live shrimp or frozen blood worms from time to time. The mouths on knives are surprisingly large. My girlfriend's knives grew to be over a foot and a half.