I like all of them. I just wanna know ALL of options of fish. hahaha. I'd like to keep a lungfish but i'd need a larger tank for that.Senegal and Delhizi bichirs can both get 12" easily, and the delhizi will easily get 14" and some even more, and will do moderately fine in a 55g for life, maybe go to a 75 when they do get 12"+. They arn't eels, but they have the look of them. If you want a true eel, you could try a smaller spiny eel, peacock eel, or tire track eel.
I'm talking about picking ONE and sticking only ONE fish/inhabitant ina 55g in total.
Also like snakeheads and bowfins.