I feed my bichirs live food. Bichirs can realisticly eat anything that is up to 2/3s their body length, but a fish that is 4-5 inches may be hard for him to catch. Mine are 5-6 inches, and I feed them guppies, rosy reds, and ghost shrimp, they can eat about 10 a day actually. If you are jus ttsarting to feed them live food, get ready to start seeing some growth spurts. mine get live food every couple of months. And they get forzen silversides every other week. They go through growth spurts after ever feeding of live fish, and when I started them on the silversides, tehy started another growth spurt.
At one time, I only had 1 in there, and it took him months to go through all the live food in the tank, when I put in another bichir, tehy clear the same amount of food in a few days now...with the help of a few carniverous catfish as well.