The tank doesn't need to be to big, a 75 gallon would be fine. (They spend a lot of time curled up.)
Ropefishes (Erpetoichthys calabaricus) are bichirs in the family Polypteridae. They grow to three feet, as UncaBret said. They need plenty of places to hide and are primarily nocturnal. These fish are carnivorous and small fish will get eaten, but they are not aggressive.
They will eat pellets, beefheart, frozen and freeze-dried food, as well as live foods such as shrimp, earthworms, and feeder tetras (which should be quarantined and Gut-Loaded).