Here's why:
* No external sex organs: Goldfish don't have visible external sex organs like some other animals.
* Similar appearances: Both male and female goldfish have the same basic body shape, fin structure, and coloration.
How to determine sex:
* Breeding season: During breeding season, males develop small white bumps called "breeding tubercles" on their gills and head. These tubercles disappear after breeding.
* Egg laying: If you have a group of goldfish, the female will be the one that lays eggs.
* Expert examination: A veterinarian or experienced fish breeder can sometimes differentiate sexes based on internal anatomy, but this requires a more invasive examination.
In conclusion: While there are ways to tell the sex of a goldfish, it's not possible just by looking at them.