Xenomystus

The African knifefish, Xenomystus nigri, is a notopterid recorded from numerous African rivers, including the Nile, Congo and Niger systems. Its swim bladder acts as an accessory breathing organ, and it rises to the surface periodically to gulp air, often with a bell-like sound. Often confused with the far more aggressive Asian knifefish, Notopterus notopterus, it lacks the dorsal fin present in its Asian relative. A scaleless species, it is very sensitive to medications.