Emperor Tetras are highly sexually dimorphic and thus males and females are quite easily distinguished from each other. There are several ways to tell a male and female apart, the most reliable method is to observe the eye color. Males will have metallic blue eyes while females possess metallic green eyes. Also, the male has a three pronged tail with the medial black stripe usually extending beyond the rest of the tail while in the females this median black stripe will typically only reach as far as the clear part of the tail. However, this is not always the best indicator as the third prong in males can sometimes be nipped off in competitions with tank mates and more dominant females may sometimes grow this extension of the tail as well.