What is the difference between male and female fish?

Answer 1

for most fish looking at the anal and the vent is the most effective way to tell. on females the vent is often bigger then the anus and on males the vent and anus look the same size. this often takes some practice but after a while it will become fist nature. this isn't true for all fish just most of them so do your reaserch to make sure you can. good luck
Typically the female fish is bigger than the male fish. Females lay the eggs while the males fertilize them.
The male fighter is more colourful and has longer fins than the female.

Answer 2

That depends upon the species. In some species there is no visible difference in others the difference is so great as to make the fish look as if they are entirely different species.