i have a 7" Senegal in my 29 gal, i think its to tiny for him so soon he will be in the 180, its just that they need more space to swim because mine is always active
in a 29 ansorgii if you could ever find one but a 55 would be better why not try a senegal or another small bichir in the 55 with the jackdempsy that could work if its female mabye male but thats pretty risky