Bichirs are predatory fish and in captivity will take any live or dead animal that can be swallowed or broken apart and then swallowed. The only thing preventing a bichir from emptying an aquarium of smaller fish is its speed; the pectoral fins only allow for slow cruising, and while it can achieve amazing bursts of speed, it can't catch fish of average speed. Given enough time, any fish that can fit in the bichir's mouth will be eaten. This fish should not be kept with any other fish smaller than three inches.
I've had Senegal Bichir for about 5 months now. It's actually a pretty peaceful fish. I have it with a bunch of Gouramis and tetras. But, if the fish is small enough to fit in its mouth it will hunt it and eat it whole!
I'm in love with these guys. They're smaller than their much bigger cousins and a lot more active during the day too. Mines like to hide in the java mass or sleep in her log. She likes to ambush prey like shrimp and small fish. Also bichir gulp air, so your tanks cannot be filled to the brim or else they won't be able to breathe.
One of the smaller bichirs commonly seen. They grow to about 11"-12" give or take. Really fun to watch and great additions to oddball aquariums. These guys do better with a tank with a larger footprint. While 55s are sometimes said to work, the deeper footprint of a 75 would be more ideal. These guys seem to grow fast up till 7" inches then slow down. I feed mine beef heart, earthworms, and a variety of other meaty foods (no feeder fish though. Don't want to lose these gorgeous fish to parasites or anything else). Don't try to put small fish in after these guys are settled. Mine is only about 5"-6" and he already wolfed down two 3" swordtails and a 2" gudgeon in less than 10 minutes. Like everyone says, it's not an if thing with smaller fish, it's a when thing. All in all, if you have a big tank, give these guys a shot. They're one of my favorite kinds of fish.
Have had individual bichirs in community tanks for many years and even though they will rapidly consume tetras and swords, they have always gotten along very well with any clown loaches I had in the tank. To the point of when I unknowingly received a wild caught bichir, he slept with the clown loaches all over and under him and followed them around learning from them how to eat fish food pellets. Many amusing bichir stories available upon request.