Ropefish (Erpetoichthys calabaricus)

Ropefish are close cousins of the bichir, in the same ancient Polypteridae family and sharing that same pair of functional lungs, but they've gone even further down the eel-like path — no pelvic fins at all, just a slender, rope-thin body built for burrowing into substrate and squeezing through tank decor. That flexible, air-breathing body also makes them notorious escape artists, so a genuinely tight-fitting lid isn't optional.

Care level: Easy · Temperament: Peaceful, shoaling · Max size: ~16" · Min tank: 30 gal, tightly covered · Diet: Carnivore, sinking meaty foods