See those parrotfish? Though they look different, they actually belong to the same species. They’re called stoplight parrotfish, or Sparisoma viride, and they can change gender and color throughout their lives. As juveniles, these parrotfish appear reddish-brown; this is their “initial phase” coloration, similar to that of adult females. After they’ve matured, they can change sex and turn bluish-green, a “terminal phase” coloration associated with adult males.
Why the sex change?
It’s an evolutionary advantage. If the dominant male in a group dies, a female parrotfish can take its place as the next dominant male. It can then mate with other females and reproduce successfully, thus maintaining its population.
Other things you probably didn’t know about parrotfish:
- They wear pajamas. At night, they can secrete a mucus cocoon to mask their scent from sharks and other predators.
- They poop sand. They use their beak-like teeth to grind up coral, digest it to absorb its nutrients, and then excrete it as fine white sand.
- They have mustaches. Over time, as algae grows on parrotfish mouths (the area from which cleaner fish stay away), it starts to resemble facial hair.
…You knew I’d bring up sea hares again, didn’t you? Well, unlike parrotfish, they can’t change gender, but they have both male and female reproductive organs. When they mate they form chains (or “conga lines” as I like to call them) in which each individual serves as both a male and a female, altogether producing HUNDREDS OF MILLIONS of eggs. Only a small fraction of those survive, but still, how’s that for an evolutionary advantage?