These are pretty sensitive fish, and would likely not survive in a 75 with an Oscar. Either that, or the Oscar won't survive with the bichir. When they begin to feel overcrowded, they become violent, and they are outfitted to kill.
The good news is that, as your Oscar grows, and you get more interested, you might end up upgrading to an even larger tank, and the bichir will probably make a good tankmate in a 100g+ tank. It needs a lot of plants, soft substrate,
driftwood, and some form of caves. In addition, it needs lateral space. Depth means nothing for these guys, but the need a lot of space to lay down in.
Lastly, and most importantly, they need a tight-fitting lid with no gaps. They have a "lung," and can live indefinitely while the skin remains wet. The thing is, when escaping, they don't understand that there is no other water nearby and no way to get back to the water when they escape, so they are often found as a piece of fish jerky on the floor.