The serpae tetra (Hyphessobrycon eques) also may be called the jewel tetra, blood serpae or red minor tetra. This fish popular freshwater fish does best in schools of five or more, and you'll most likely have mixed genders in your aquarium. Whether for curiosity's sake or for breeding purposes, you should be able to identify the genders of serpae tetras in your aquarium.
Females are Dull and Round
The differences between male and females serpae tetras are slight but with a close eye, you can distinguish the difference. Males are generally smaller than females, but they have a vivid red color. Females tend to be a dull red and are round, especially during the mating process when they tend to become much fuller than males.