Editor's Note: William Gilly, a professor of cell and developmental biology and marine and organismal biology at Stanford University, is traveling with a group of students on board the Don José in the Sea of Cortez. They will monitor and track Humboldt squid and sperm whales in their watery habitats. This is the group's seventh blog post.

SEA OF CORTEZ—In our pursuit of discovery, we have snorkeled four times in the last two days and completed three intertidal transects. The diversity and beauty in the Gulf of California continually challenge us to open our minds to new organisms and concepts, and I have learned a great deal about the bright fish that swim across our path. It has come to my attention that Cortez wrasses (Thalassoma lucasanum) have a particularly interesting life cycle, and I hope to impart my new knowledge in this area to all the wrasse parents I have seen swimming beneath us.

What is Happening To My Body: Instructions for Cortez Wrasses

An Introduction for Wrasse Parents: There comes a time in every wrasse’s life when intertidal algae no longer hold any mystery and lights from Christmas-tree worms no longer warm the soul. This time is called puberty, and these instructions are intended to answer the many questions that may float unspoken between adult and juvenile wrasses as these many changes unfold. Of course we all know that wrasses are protogynous, but this fact still leaves many wrasses unprepared for the raging hormones and internal reconfigurations that come with changing from a female to a male. Perhaps this surprises you elder wrasses—it has been so long since you yourself made this leap. But try to remember what it felt like when you were no longer the belle of the intertidal ball and no longer led group spawning as an egg-filled female, but began to participate as one of many eager adult males. Then maybe you can recapture some of the excitement and questions that accompany this monumental change.

And maybe you will remember how confused you felt as your four- to five-inch body morphed from female to male. Bear with your young wrasse; if young Alexandra—now Alexander—comes back to your rock crevice and refuses to cover himself with sand, he is just asserting his independence as a newly formed male. Let him be dangerous—he will soon grow out of this rebellious stage with a little nurturing. Sometimes sneaking extra crustaceans into his path, or allowing him a prime cleaning spot on some passing fish, will help boost his confidence so that he embraces being a male. While we all think of our female days fondly, it is not the way of nature for us to be that way always. And with a little luck, your Alexander, or Michelle turned Michael, will become a large and dominant individual, one of the few ornate secondary-phase males. At this stage he will change color from red, black and yellow horizontal stripes to large chunks of blue, red and yellow. Now he can one-on-one mate, and that is something that every parent should anticipate with pride.

By reading this book, you and your young and newly male offspring may successfully and quickly come to terms with the beauty that is protogyny, and our wrasse way of life.

Image of Sea of Cortez wrassesfemale juveniles and male adultscourtesy of Micki Ream; image of colorful secondary male Sea of Cortez wrasse courtesy of Micki Ream.