Well personally I suggest setting up the new tank as if the Bichir was fully grown and overfed a bit. That's the way I set up this 150 gallon for my Blackbelt. There are so many "right ways" of doing things that it's impossible to tell you the way to do it right in such a small writing, but just keep in mind that your fish would want as much room and filtration as possible without blowing him around the tank with water current (which will be hard to do). Plan on doubling what manufacturers suggest and you will be close to what I'd suggest! My fish is beefy/tall-bodied, and eats alot, but isn't as messy as an Oscar or similar, but I chose a 5'x2' 150 gallon tank (about 125 actual volume) for him. with a 26 gallon wet/dry sump run by a pump doing approximately 600 gph, and a Filstar XP-3 canister (350 gph). I also run a powerhead pumping 350 gph with a prefilter. This adds up to about roughly 1300 (probably less) so it's maybe 7 or 8 times turnover per hour, actually. Better to err on the side of caution, don't you agree?