Transition across polymorphic phenotypes observed in a male Sternarchogiton nattereri (Gymnotiformes: Apteronotidae).

A transition between polymorphic phenotypes was observed within a single male Sternarchogiton nattereri. This individual was initially toothless, but developed into a toothed phenotype characterized by a swollen distal upper jaw and distinctive external dentition. Changes in morphological features were accompanied by shifts in electrocommunication (chirping) behaviour.