The Amazon basin has a freshwater fish diversity comparable to a tropical sea. Although many Amazonian fish species are popular ornamental fish across the world, the ecology of most species in their natural habitat remains poorly known (van der Sleen and Albert 2017). We report on shoaling behavior in Platydoras hancockii in a floodplain forest of the middle Rio Negro, Brazil. As the shoal consisted of only adult males, whereas gravid females were caught individually in nearby areas, we hypothesize that this aggregation may relate to spawning. Moreover, considering that Platydoras hancockii is capable of producing sounds, it is possible that these aggregations entail the formation of a chorus-like call with the function of attracting females from a larger area.