The bony-tongued fish that hunt with electricity and bite with their own mouths

Nature · Published 3 October 2026 Swipe more like this →

In short: Known as Osteoglossiformes, these primitive, heavy-bodied fish are defined by a bizarre anatomical quirk: they use their tongues to bite into food. Found across tropical freshwater environments, this diverse order includes everything from tiny two-centimetre minnows to the massive arapaima, which can grow to over two metres in length.

The order Osteoglossiformes, or 'bony tongues,' represents a lineage of ray-finned fish that has existed since the Early Cretaceous period. While they are primarily freshwater inhabitants found in Africa, Asia, South America, Australia, and the tropical Pacific islands, their evolutionary history is deeply tied to the ancient supercontinent of Gondwana. Their distribution across these disparate landmasses suggests they originated before the continent fragmented, though recent fossil discoveries in marine environments indicate their history may be more complex than once thought.

Physically, these fish are distinguished by large, hard scales and a primitive jaw suspension. Their most striking feature is the primary bite of the mouth, which occurs between the parasphenoid bone in the skull and the tongue itself, which is equipped with well-developed teeth. Internally, they also possess a unique gastrointestinal structure: the forward part of the tract passes to the left of the oesophagus and stomach, a trait that sets them apart from all other fish, which typically pass to the right.

Beyond their anatomy, some members of this group, such as the Mormyridae and the African knifefish, have evolved the remarkable ability to generate and detect weak electric fields. This biological sonar allows them to navigate and communicate effectively in murky, low-visibility waters. While some species are strictly freshwater, a few are known to occasionally venture into slightly brackish environments, showcasing a surprising level of adaptability for a group often labelled as primitive.

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