The recently described Poecilocharax callipterus, male above and female below. Notice the dimorphic coloration and dorsal- and anal-fin elongation. Males are reddish in color and slightly darker than females and have a conspicuously long filament on the dorsal and anal fins. Dimorphism is a term scientists use to describe the differences in appearance between males and females of the same species. Fish size ~3 centimeters.