Unlike other members of the genus Sternarchogiton, there is pronounced sexual dimorphism in S. nattereri, with reproductively mature males developing strong external teeth on tips of their jaws.

These males are so different from the females and juveniles that they were thought to be a different genus and species, the "tooth-lip knifefish" Oedemognathus exodon, for over 40 years.

[1] In reproductively mature males, the head becomes elongated and prominent external teeth develop on the upper and lower jaws.

[4] The diet of S. nattereri consists of freshwater sponges growing on submerged trees, stumps, and other woody debris.

[6] The external teeth of male S. nattereri are now thought to be used in combat for territory or mates; scars and scratches have been found on the napes of several specimens.

[4][7] In the Tefé region of Brazil, breeding occurs during the rising water period, with adults spawning in floating meadows along the edges of paraná channels (side branches of whitewater rivers that run through adjacent várzea floodplains).