African Knife Fish (Xenomystus nigri)

African knife fish lack a dorsal fin entirely, relying only on a long undulating anal fin running most of the body's length for propulsion — letting it hover, reverse, and maneuver with a precision dorsal-finned fish can't match. It's also an accessory air-breather, gulping air at the surface to supplement gills in the low-oxygen swamps and backwaters it calls home.

Care level: Moderate · Temperament: Peaceful, territorial with own kind · Max size: ~8" · Min tank: 40 gal · Diet: Carnivore, live/frozen foods