You're talking about a fish (clown knife) that in the wild has reached 50", and that when raised in a tank has reached 30-40" (and that grows quickly as well), so no, not for life.
Also, a fire eel (which also gets enormous and grows quickly) would probably do best if it had at least the whole tank to itself. If there were any new additions, I'd lean towards much smaller ones.
There are of course many other options, but not having any knowledge on lap bichirs, I'll pass on making a suggestion.