The Blue Groper fish have a unique way to control their population: they can change their sex!
Bob Harcourt, Associate Professor Macquarie University: "The blue groper is a large fish, but the really sexy thing about Blue Groper is they start off as females. We've got lots of blue groper that are small green groper and as an old male dies then the largest most dominant females turns blue and becomes male.
And so one of the really cool things about these fish, is the sex ratio doesn't really vary, but it is a function of how well protected they are. If you take a lot of males out, then the females have to spend a lot of their time turning into males, which means they can't breed and they can't lay eggs."
Now, the blue groper may be in danger. Their population has crashed and scientists are trying to figure out why. National Geographic has the video clip: Link - Thanks Marilyn!