The sexual orifice in fish. The sex glands in females are ovaries: they form oocytes, which are commonly referred to as eggs. The mature eggs are excreted through short ducts that open into the cloaca or genital opening. Some species of round fish do not have such ducts, so the eggs come out in the cavity, then - through the urethra. According to the shape of the genital opening can be established sex and degree of maturity of fish of many species.