Sheephead fish: sex change without surgery

Photo credit: Magnus Kjaergaard

Photo credit: Magnus Kjaergaard

It’s Friday night at the local saloon and not one person of the opposite sex in sight. Dating can be such a drag. But instead of moping, why not head to the restroom and perform a quick sex change and become the hottest commodity at the bar?

Welcome to the potential benefits of being a California sheephead fish. Well, it’s not exactly a quick phone booth style transformation like Clark Kent to Superman. But Semicossyphus pulcher, the scientific name for the California sheephead fish, does begin its life as a female and then transforms to male later with the potential to grow up to three feet long.

This transformation is old news to scientists and fish fact fanatics, but still fantastic!

Another fantastic characteristic of the sheephead fish is their teeth. They possess huge chompers allowing them to eat a variety of hard-shelled creatures such as crabs, clams and sea urchins, and placing them in an important role for maintaining balance in California’s ocean ecosystem.

But enough about teeth, let’s get back to sex! The sex change trait is called protogynous hermaphrodism, excellent lingo to stump friends with the next time you’re having drinks or stuck at the bar without members of the opposite sex.

Not to break form with humans, female California sheephead fish begin their lives wearing pink, kind of a mauve reddish pink with a white chin. Then once the sex transformation takes place and the female becomes male, the head and tail turn black but the midriff remains reddish pink. The males continue flaunting a white chin, the polar opposite of a man’s black beard.

But how does this sex change really work?

Similar to other species’ mating strategies, male sheephead fish need be able to defend a territory or ocean plot from predators and other sheephead males interested in the same ladies. This requires bulk and the ability to be aggressive. Once a female is able to fulfill this more domineering role, it only takes hormones to jump start this life-changing transformation.

UC Santa Barbara researcher Jennifer Caselle graciously explained the details to me, “It is hormonal changes that cause functional ovaries to transform into functional testes. The ovaries literally change into testes,” she said. “For fish, these structures are relatively simple. A lot of the specifics are still unknown, including the hormones that kick off the process. These fish spawn externally so that means that they rise up in the water column and release eggs (female) and sperm (male) where fertilization takes place (outside the body). Yes, the ‘hole’ is the same, fish are relatively simple in this department.”

The reason ‘hole’ has single quotation marks around it is because she is quoting my email asking if eggs and sperm are distributed through the same hole. Of course I had to know this!

Now that the sex change process is a bit clearer; we turn to more existential questions.

And who better to turn to for an expert opinion on the love life of a fish than Dr. Milton Love, a marine biologist at the Marine Science Institute and author of Probably More Than You Want To Know About The Fishes Of The Pacific Coast. An expert ichthyologist (a biologist who studies fish) with the last name Love has to have the answers.

In his book, Dr. Love takes more of a philosophical approach to understanding fish gender transformation.
“Personally, I think it’s neat to contemplate the effect on our society if we changed sex,” states Love. “Consider for a moment if most humans changed sex when they were 30 years old. Sexism would be less common as all of us would understand what both sexes experience.”

This reflection inspired him to write the following limerick: “There are fishes, we scarcely dare mention, with behavior that merits attention. At ages quite tender they blithely change gender disdaining the normal convention.” (For the full limerick see Dr. Love’s book Probably More Than You Want To Know About The Fishes Of The Pacific Coast.)

But alas, for the California sheephead, times have changed and their sex change is no longer as acceptable as it used to be, but not for the typical reasons humans debate.

In an ongoing study by local scientists from UC Santa Barbara and CSU Long Beach, research indicates that large sheephead males are strangely absent near Catalina Island. Without large males available, females may be changing sex earlier than normal to fill the void.

But as always, there is more to this story than meets the eye.

Dr. Chris Lowe, Professor of Marine Biology at CSU Long Beach explained that research at San Nicholas Island found a ratio of four females to every one male sheephead, which is the typical arrangement historically; while data gathered at San Clemente and Catalina Islands found a ratio of one female for every one male sheephead.

And the main difference between these sites is fishing access. San Nicholas is used by the Navy for weapons testing and is a highly restricted area, while San Clemente and Catalina are easy to access for fishing.

But the different gender ratios are still puzzling because usually large sheephead males breed using a harem style set-up, fertilizing as many eggs as possible from several females. But how does the harem lifestyle change with a female for every male?

Figuring this out will require additional research observing sheephead behavior during breeding season at each location. Not an easy task.

“One of things that Jennifer Caselle, Kelly Young and I have noticed in our research is that females at Santa Clemente and Catalina Islands are transitioning to males during the breeding season. And this is an unusual situation because that means those fish are not able to breed that year,” said Lowe. “Unfortunately, it’s not clear why they are transitioning during the summer or how long the transition takes. Nevertheless, it looks like fishing pressure is playing an important role. But these are the southern most of the Channel Islands we’ve studied and it’s possible that oceanographic conditions or diet may also influence this unusual sex transition pattern.”

With fewer and smaller sheephead fish, UC Santa Barbara postdoctoral researcher Scott Hamilton said, “This can have important implications for kelp forest ecosystems because sheephead are one of the main predators of sea urchins (along with lobsters) in southern California. By eating urchins, sheephead may help control the formation of urchin barrens.”

Based on detailed diet studies Hamilton is doing with several other researchers, only the large sheephead fish with the biggest chompers are eating urchins. So without as many large sheephead fish chomping urchins, more urchins are left to gorge on kelp.

Wow, all this outfall from an early sex change! Not good.

So the next time you’re sipping a beer on a Friday night, bummed to be surrounded by members of the same sex, take time to raise a glass and toast the California sheephead fish who could change from female to male in a similar situation without worrying about having to explain it to her parents. Let’s just hope she waits and reaches a healthy larger size before making the switch.


  1. Abraham says

    This is awesome! I toast to you sheephead fish, for only you will know what women really want, well eventually of course…

  2. Alexis says

    I really loved this article! But i was kind of hoping to see how the sheephead reproduce if there are only male adults and no females. I mean don’t all of you think that would be an interesting?

    • Carolyn Kraft says

      Hi Alexis, Alas, if there are only male sheephead adults around, they can’t reproduce! Once a sheephead has transitioned from female to male, there’s no going back. That’s why females don’t typically transition to male until the male in their territory has either left or died. This is their way of avoiding a sheephead sausage party so to speak.

Leave a Reply

Your email address will not be published. Required fields are marked *