Determining the sex of cockerels (Betta Splendens) - in comparison with other aquarium fish, determining the sex of cockerels is quite an easy task.
The male cockerel fish is slimmer and brighter in color, has longer fins. Female cockerels are often smaller and have short fins. The main distinguishing feature of the female is the presence of a small "white grit" on the abdomen near the anal opening.
the main feature distinguishing the female from the male, which is noticeable already at 3 months of age:
This feature does not give a 100% guarantee, as it occurs in young males.