Depending on the species, determining the sex of a fish ranges from easy to nearly impossible. These tips will help you sex common species of aquarium fish.
This is by no means an exhaustive list, but does provide a general overview of the differences between the fish sexes. If you need help with a specific fish, send me an e-mail and I'll give you details for that species.
Angelfish Gender
Angelfish are nearly impossible to sex accurately. Occasionally fully mature males will show a modest nuchal hump, which is a bump on the head just above the eyes. However, don't count on it.