I am saying you could keep the lungfish for a few years, and it could live with things greater than or equal to the size of a congo tetra. A royal knife would get too big. You could keep an african knife, a mottled, brown or black ghost. Never mix two ghost knives or an african with a ghost. Their electrical currents will meet and they will fight. A good community oddball tank would be with plants and caves and 2 indo dats, 2 polypterus endlicheri's and/or 2 polypterus delhizi's, an african knife and a tire track eel. As for feeding the bichirs, dats, and knife will eat most foods that can fit in their mouths. And the eel will eat earthworms and possibly frozen foods.