How can some fish change from female to male?

Parrotfish an anemonefish can live for a while as male or female – but different hormones kick in and cause it to change.

No fish can reproduce immediately after hatching from its egg. Like humans, fish have to mature before they can reproduce.

As a fish matures, hormones are released. These are chemical signals that travel through the blood to the rest of the fish’s body – they stimulate the fish’s reproductive organs to begin to change.

If the fish is to become a female, then the reproductive organs produce fish eggs – as well as other hormones that cause the fish to behave, look, and function as a female. In males, the reproductive organs produce sperm cells – and the fish begins to behave, function, and appear as males do.

In fish that change gender – for example, parrotfish or anemonefish – only parts of the reproductive organs mature at first. The fish lives as a male or a female for awhile.

But – when the fish reaches a certain age, or its mate dies – those initial reproductive organs wither away – and other reproductive organs mature, so that the fish becomes the opposite sex. And what causes the change? The answer is hormones – or chemical messengers in the blood.