Ok, so, a few weeks ago, i saved a senegal bichir from my little sisters' class. it lived in a 5 gallon bucket with 2 inches of gross, cold water. here is his story. he was purchased at petco
(i DO NOT like petco) and lived in the bucket. i took him home (the teacher wanted me to, so they didn't have to care for t over the summer) and put him in one of my many tanks. he has moved through all of my tanks, because he kept trying to eat every thing, and a thought he was a horrible pain. now i have him all alone in a 15 gallon tank, and i love him. i might have some room for him in the 120 gallon, or the 900 gallon indoor archerfish pond. 'm waanting to know some tankmates for him, after seeing a 3 inch fish scarf down 30 feeder guppys and a ghost shrimp, i'm scared of keeping him with any thing!!!!!!!!!!!
The bichir will need at least a 48"x12" (imo) to be happy. They are very active animals that need lots of room to move around. They can get up to 12", but you will usually only see them around 8-10". Tankmates should be chosen wisely... anything that can fit in the bichir's mouth will become food and anything that can slurp the bichir down won't hesitate.
I love bichirs (I own 8 different species) and think that the 120 is a great tank for them. Much better than in the 15 and in the 900, I'm sure you are going to have fish that are too large for the bichirs. They can easily become spaghetti.
Feed them meaty foods: bloodworm for starters, beef heart, earthworms, uncooked shrimp, strips of whitefish, ghost shrimp, pellets, etc. I would stay away from feeder fish, unless they are guppies that are quarantined before feeding and only as a treat.
You can keep different species and sexes together, with no problem, as long as you don't mix the larger lower jawed species (endlicheri, congicus, lap) with the smaller upper jaws (palmas var, delhezi, senegalus).
I hope that helps!
EDIT: I also want to add that you should not choose tankmates that are very fast and quick to eat all of the food, as bichirs can be pretty slow to find food, as they are pretty blind.
They rely mainly on their sense of smell, which can sometimes slow them down. As they get used to your feeding schedule, they get better at getting the food, though.