According to Wikipedia
How many animals can change gender?
Animals that can change sex. There are species that have the ability to change their sex and/or appearance. While there are over 1,500 species that exhibit homosexual signs, there are also animals that are ‘gender-bending’, with the ability to change how they look and/or their biology.
When animals change their gender?
Natural sex change, going in either direction, has even been reported in certain types of corals. Usually sex change in animals is due to necessity, from changes to environmental or social conditions. One animal you might be surprised can sex change are chickens, which occasionally switch genders from female to male.
Can frogs change their gender?
Frogs. Researchers have observed frogs spontaneously changing genders in the lab. Now they’re observing it in the wild too, and it’s not a natural process. More and more male frogs are becoming females, complete with fully functioning reproductive organs.
Can reptiles change their gender?
That’s right: In warm environments, a type of lizard known as the Australian bearded dragon can switch from having its sex determined by genes to having it determined by temperature. Some types of fish can reverse their sex — for example, parrotfish start life as females and change to males.