You need a 90g. Bichirs get around a foot, minimum, depending on the species. You need a sand bottom, the finer the sand the better, and they need plenty of hiding places. They're predators, they can't see well, they go by smell. They're nocturnal, but they'll go to the surface to gulp for air. They can escape if the tank's too full. Planted tanks are good, plenty of hiding places. They'll eat a wide variety of foods. Fish small enough to fit in their mouths, worms, dead things, and even insects. They'll death roll like crocodiles and alligators if they can't fit in their mouth. They grow fairly slow. They "walk" on the sandy bottom, so finer sand is better.