Whats the sex of my Corys ???

[Jmoto]

i got 2 juli corys and im gonna buy 2 more i want them to start breeding but i dunno how to tell there sex

 

[Tokis-Phoenix]

Females are larger and more robust looking than the males, males are small and more streamlined than the females- most lfs's sell corys quite young so they are not easily told apart gender wise.
Corys are egg layers and need very good water quality to encourge them to spawn and practically all other fish prize their eggs as very tasty snacks, a newly cycled or cycling tank will be unlikely to incourage them to spawn.