1. Yes, they can be kept together; a 40 gallon breeder would be ideal, imo.
Best go for a 75gal minimum, 40gal is tiny even if its a breeder tank. For a fast moving close to a foot long when mature african knife that darts about the tank at speed in and out of cover you will need a 75gal 4ft long minimum as they need the space to move at speed. The bichir will get to a similar size but is nowhere near as active but 2 x 12inch long carnivorous fish in a 40gal tank does not sound quite right to me. I have been keeping african oddballs for years and have a knife that ive had for over 8 years now. I also have a 40gal breeder tank that i used for a couple of axolotls and that tank would be nothing more than a cramped temporary hospital tank if it ever came down to it.
Diet wise pellets are a no go with mine (each to their own i guess), hes just not interested. He's very much a meat eater so its bloodworm, chopped shrimp, chopped mussels, chopped cockles and earthworms for him.
They love their caves, plants and bog wood structures and if you get it all right they are incredibly friendly, active fish and a joy to keep.
If i was you get the biggest tank that space and money will allow and go for an african riverine biotope, some large african tetras along with your bichir and knife would be the dogs danglies!
Any questions man just ask, i love my african fish. I have a 900gal slice of the congo in my living room in the pipeline which is all very exciting!
Ed
