Distinguishing fish by sex is not easy. This can be done only visually, but, in this case, the result may be unreliable. It is much easier to ask the seller right away when buying. But even a person who sells fish does not always know who is male and who is female. Try to make a comparative analysis of individuals by their appearance.
Determining the size of the sex of the fish is quite difficult. Females are not always smaller than males. In the period of preparation for spawning, females have an increase in the size of the abdomen, while in males everything remains the same.
It is worth paying attention to their color. Males have a bright color, while females, on the contrary, often have a nondescript appearance.
The fins and tail of males are usually longer than those of females. The color is bright, saturated. Changes in the color of the fins are sometimes noticeable during the spawning period. At this time, they become even brighter, additional pigmentation appears.
The fin coloration of females remains unchanged.
If you cannot distinguish a male from a female, but you see a visual difference in their structure, then, most likely, you have different-sex fish and, perhaps, offspring will appear in the near future. If there is no difference, then contact the pet store. Consult a specialist and buy another fish.