Sex-changing fish: Secret lives of bluebanded gobies
February 2nd, 2013
05:00 AM ET

Sex-changing fish: Secret lives of bluebanded gobies

By Kelly Murray, CNN

What would it take to change sexes? In humans, it involves complicated surgeries and rigorous hormonal therapies, not to mention hefty social and psychological ramifications. But in the Eastern Pacific Ocean, tiny orange-and-blue fish are naturally transitioning from female to male, and male to female, all the time.

Bluebanded goby fish, about 2 to 2.5 inches long, are able to change their sex when it suits their position in social hierarchies.

Matthew Grober, associate professor of biology at Georgia State University, has received funding from the National Science Foundation to better understand what mechanisms cause some of these fish to change sexes. In his lab, fluorescent lights accentuate dozens of aquariums lined with grayish-green algae where his bluebanded gobies thrive.

“We can detect within minutes, via changes in behavior, when a fish begins the transition, and it generally takes one to two weeks to complete the transition from female to male,” Grober explained.

One indicator of typically male behavior is movements associated with male courtship, such as rapid zig-zag movements called "jerks," as described in a 2007 study that Grober co-authored. Females that become males may also reduce their submissive behaviors.

Although natural sex change is exceedingly rare across the animal kingdom, bluebanded gobies are not the only creatures capable of it. Other examples include the clown fish and the limpet snail.

Groups of these fish have a skewed sex ratio in their natural environment. In other words, goby groups are not 50% male and 50% female, as one might expect. Instead, as Grober explained, “Gobies most often live in groups called harems that usually consist of one male and four to five females.”

In a natural setting, if the leading male dies, the most dominant female remaining in the group will take leadership of the harem and then physically change into a male.

Why would the female change her sex? The answer lies in evolutionary biology.

An organism’s evolutionary success depends on the number of genetic copies of itself it leaves behind in the population. So, a male fish, which mates with all of its harem’s females, has much more success in spreading genes than any given female.

For example, a male in a harem of four females has four times more reproductive success than any of his females because each individual female has only the harem’s one male partner with whom to mate.

Just as in humans, in many sex-changing fishes, social context often determines an individual’s behavior.

The bluebanded goby observes and reacts to the behavior of others around it, so as to optimally position itself within the social hierarchy. Other fish observe that individual’s behavior and react to it, and so on.

Grober wanted to know if the same mechanisms that regulate female-to-male sex change also work in the other direction. Using saltwater aquariums in his lab, he designed an experiment that used isolated groups of all males and all females.

Each group had one fish that was significantly larger than the others to encourage one individual to achieve dominance over the rest of the group. Grober and others argue that while a larger fish is more likely to achieve social dominance over its smaller harem mates, size alone doesn’t completely determine which fish is the most dominant.

His research group observed instances of aggressive behavior (approaches, flaring fins, head-standing) and submissive behavior (retreat or avoidance in response to aggressive behavior) in these groups. Taking all individual interactions into account, they could determine each fish’s social status within the group.

The fish demonstrated male-to-female sex change in this experiment. But something else remarkable happened: One of the fish remained male, and it was the only fish to retain its dominance over the group.

For sex change in either direction, there seems to be one guiding social principle: If subordinate, be female. Because each group had only one dominant individual, each group ended up with only a single male.

Hormones also play a role in the sex changes of these fish.

In one experiment, Grober and colleagues set up pairs of female bluebanded gobies, so that one fish was clearly subordinate. When they loaded up the subordinate with a potent male hormone, 11-ketotestosterone, it was able to make her look like a male, but her female-typical social behavior didn’t shift in a male direction. She continued to behave as a female.

“My team successfully demonstrated that while hormones do have a direct effect on the fish’s physical structure (like gonads, genitalia and fins), the fish's behavior answers more to its position in the social hierarchy,” he said.

So what can we Homo sapiens learn from these fish?

Researchers’ efforts are showing us that two seemingly distant vertebrates actually share quite a lot of characteristics. As Grober firmly asserted, “Us IS them.”

In both people and these fish, behavior answers to social context; it’s only partly determined by physical sex and size. Sexual behavior in humans and gobies is malleable: It is able to change based on an individual’s placement in the social hierarchy.

Grober argues: We should not think of fish as being like robots or automatons, because they make complex decisions regarding reproduction just as humans and other social animals.

More on the bluebanded goby’s amazing sex-changing ability

Other animals that change sex

Post by:
Filed under: Ocean exploration • On Earth
soundoff (71 Responses)
  1. cassidy


    February 5, 2013 at 12:39 pm |
  2. j was censored on CNN, multiple comments never posted par let's golf

    Chickens naturally hermaphrodite; Do you agree?

    February 4, 2013 at 5:57 pm |
  3. j is censored


    February 4, 2013 at 4:35 pm |
  4. empresstrudy

    But can they be mayor of San Francisco

    February 4, 2013 at 2:51 pm |
  5. USA

    WOW! Didn't know that 🙂

    February 4, 2013 at 1:36 pm |
    • Christopher

      This is not news. This has been known for many years and it's not just this fish that can do it.

      February 4, 2013 at 2:04 pm |
  6. RandiRN

    If fish can do it, why then is it so unbelievable that people find that their minds and bodies don't match? Those that are born with this birth defect are often ridiculed, and made fun of. Just read the comments by the ignorant folks who post them? People born with minds and bodies that are in-congruent often commit suicide to make the pain go away. These fish adjust to the needs of the community. How wonderful if people would accept someone getting their minds and body match.

    February 4, 2013 at 12:21 pm |
    • supporting

      Thank you for the support and knowledge sharing. Many here on the listing will never understand until it is their child, mother or father or other family member that is incongruent. It is crude and inhuman to have such views of others that you do not know and find it fun to ridicule. I am certain they are not perfect either unless they are not human beings. What if you were born incongruent? The commenters who are so righteous here need to educate themselves and identify their own fears and rise above such mediocrity. There are about 1% of the human race that are Transgendered and in ancient Indian Cultures they were revered as being healers and close to God not sins of God. Hopefully in our lifetime we will have peace and understanding.

      February 4, 2013 at 2:30 pm |
  7. Mark

    Oddly enough, I just watched Jurassic Park earlier this week.

    February 2, 2013 at 9:40 pm |
  8. Sahelll

    that male fish is super lucky!!!

    February 2, 2013 at 8:04 pm |
    • Homer10


      February 2, 2013 at 9:14 pm |
      • peridot2

        1, 2, 3...

        February 11, 2013 at 2:14 pm |
  9. colin in Florida

    There is no news in this report. Biologists have known about his for many decades. I studied this as a biology student in the early 1970's.

    February 2, 2013 at 6:32 pm |
    • everything in Moderation

      Ah, but this isn't an article in a Biology publication. It's an article on CNN, and on CNN, there are many many readers who haven't a clue that nature isn't strictly ordered according to G_d's plan of one male and one female forming a nuclear family.

      February 2, 2013 at 8:01 pm |
    • kenn

      i am not a biologist and this is new to me but it gives me information

      February 2, 2013 at 9:54 pm |
  10. oakstave

    "Westboro Baptist Church announced they will picket the fish, with signs proclaiming 'God hates Swishy-Fish' and 'Transgendered Fish and Chips will be served in Hell'. Blue-Banded Gobies had no audible comment.

    February 2, 2013 at 4:24 pm |
    • Grunged

      Thank you for the laugh. That was perfect.

      February 2, 2013 at 5:17 pm |
    • Ruby Long

      Too funny!
      No doubt it is because of this that God allows fish to go bad when not properly refregerated.
      Thinking is hard work, believing is easy.

      February 2, 2013 at 6:49 pm |
      • appapo

        Both, thinking and believing are quite hard things to do, actually. Going along with the current fad -and pretending that that is actual thinking- is easy.

        February 4, 2013 at 12:51 pm |
  11. Norman

    Didn't the taxpayers of Massachusetts pick up the tab for an inmate doing the same thing?

    February 2, 2013 at 3:08 pm |
    • Justin

      extremely funny ! needed that laugh today. Thanks

      February 2, 2013 at 3:21 pm |
  12. atienne

    Lost of fish do this. I am a clownfish breeder.... The biggest male becomes the queen.

    February 2, 2013 at 3:06 pm |
    • Kris

      So, mr. fish breeder, what's this called? You should know that, and the name of when females turn into males...

      February 2, 2013 at 4:41 pm |
      • Matt

        It is called Sequential hermaphroditism.

        I grew up in the central Pacific and kept over a dozen aquariums with tropical fish I caught. Numerous fish are born all male and a female is 'born' as needed.

        February 2, 2013 at 5:10 pm |
      • Bart

        The process where an animals starts out as a female and later turns into a male is called protogyny. The opposite is called protandry. There are even fish, like hamlets, that can be male and female simultaneously (simultaneous hermaphrodites). When they mate as a couple they alternately take on the male and female roles, so the burden of the more costly female role is shared evenly.

        February 2, 2013 at 5:22 pm |
  13. Notjealous

    Most bloggers here are so jealous.

    February 2, 2013 at 2:52 pm |
  14. FishGuy

    Try freshwater livebearers like Platies, Guppies and Swordtails. They do this too. Groups of fishes, and when conditions change suddenly one fish is changing gender. We have only X and Y chromosome, XY = male and XX = female. They have W, X and Y chromosome and some complex way of determining gender, based on which is expressed and which is not

    February 2, 2013 at 1:58 pm |
  15. Lew

    The Westboro Baptist Church is demanding the eradication of the 'Satan's Sushi'.

    February 2, 2013 at 1:53 pm |
  16. Chris

    They're going to hell

    February 2, 2013 at 1:42 pm |
    • Jimmy


      February 2, 2013 at 1:43 pm |
  17. TheAntiChrist

    An inny, an outy. An inny, an outy. An inny an outy. Doe!

    February 2, 2013 at 1:08 pm |
  18. ericgoestoholland

    So let me see if I understand: the scientists can tell when a female fish becomes a male fish because they turn into jerks?

    February 2, 2013 at 12:44 pm |
    • Ruby Long

      The article referred to behavior so more correctly the don't turn into jerks, the just act like jerks... or maybe, you remember that dance back in the '60s called the Jerk? It was kind of like the Swim.

      February 2, 2013 at 7:01 pm |
  19. msr

    Seriously, I expected the comments section to be filled with Ian Malcolm and Alan Grant quotes.

    February 2, 2013 at 12:21 pm |
  20. Ming

    Clownfish changing genders puts Finding Nemo in a new light. Marlin and Nemo were the only clownfish in their reef. No wonder Marlin went through all that trouble to get Nemo back. When Nemo grew up he was going to become a she to help keep the population up. I thought the movie was about father-son relationships, but this information makes it a lot different.

    February 2, 2013 at 12:15 pm |
    • image

      Very good article. What an interesting world it would be if humans did this. we would certainly need a bigger closet for both sets of clothes.

      February 2, 2013 at 12:26 pm |
  21. kalo

    "And then god said stone the gays, but what he didn't tell everyone is he secretly loved the transgender fish."

    February 2, 2013 at 12:11 pm |
  22. Screamer

    Michael Jackson did this back in the 90's.

    February 2, 2013 at 11:40 am |
  23. susan

    Awesome! In 100,000 years, humans will be able to do that, too, as SS couples become more and more prevalent. But then I guess it would still be a straight couple?

    February 2, 2013 at 10:57 am |
  24. Pete/Ark

    It would make Halloween easier...

    February 2, 2013 at 10:38 am |
  25. Doodlebug

    If you have settings where the grouping is primarily female, then the more aggressive female will rise to the top, with the other ones falling in line, to receive favor from her, till they can find a way to jockey into position. Ever notice when there is a large amount of women in the setting, they almost emasculate the males in their need to take over?

    I am a female, with aggressive tendencies, however – I do not group. I find that my not grouping and sticking to the edges, actually threatens the dominant group females and they basically try to do you in or ensure you lose all credibility and power.

    Women in groups are interesting.. and the quieter ones in the group that are none aggressive? Food... mere food.

    February 2, 2013 at 10:18 am |
    • Susan

      Good for you. You sound like a real team player. Luckily women like you end up alone and without any real, true loved ones by your side at the end, but I know it was so worth it for you.

      February 2, 2013 at 11:00 am |
      • me

        Why would it be lucky that she end up with no friends/family???? I think you may be one of those group females that she is talking about avoiding.... I wonder why....

        February 2, 2013 at 1:45 pm |
  26. Jeebuusss

    The religious nutters constantly scream about this or that not being natural, especially on topics of sêxual orientation and behaviors. The reality is, the variety of séxual behaviors found in the natural world is staggering and just that: widely varied. Yet again reality stomps on those who spew stüpid out of their mouth that they made up off the top of their head.

    February 2, 2013 at 10:12 am |
  27. Meki60

    just like Obama

    February 2, 2013 at 9:58 am |
  28. derp

    That fish is sinner.

    February 2, 2013 at 9:31 am |
  29. Al

    I don't think we should always compare ourselves to animals and try to emmulate them. Alligators cannibalize their young and male lions kill lion cubs that aren't from them as well as try to kill every other male lion they see. Dung beetles eat other animals' poop. Etc etc. So, yeah...

    February 2, 2013 at 9:26 am |
    • Al

      I guess there are some good survival tips we can learn from them. But still

      February 2, 2013 at 9:29 am |
    • Dan

      Exactly, its so ridiculous when people use (usually rare) animal behavior to justify anything and say its natural. We could condone about anything if we actively search for a reason to say its right. I wonder when it will be accepted to marry your sister/brother/mother/father. Animals incest happens, so it must be natural. Parts of the South will be thrilled

      February 2, 2013 at 10:57 am |
      • cowdog

        Somebody needs to DO SOMETHING about the incestuous animals, Who knew? Next thing you know, dogs and cats will be living together.

        February 2, 2013 at 11:13 am |
      • jnail7

        From what I have seen about the arguments, the only time one side points to occurrences in nature is when they are countering the standard ad hominem standard of "x is not natural". This is, of course, also fallacious as is arguing based on a literal definition of "natural" than what was intended. In the end, it is what most arguments devolve down to, individuals shouting past each other and not trying to hold honest communication about actual issues.

        February 5, 2013 at 11:43 am |
  30. kanye west

    I aint no g@y fish. But I do love fish diiicks....sticks

    February 2, 2013 at 8:42 am |
  31. Equalizer357

    now, now's a FISH..! dont, ever, ever, emulate a fish,,,ever....else grow gills..

    February 2, 2013 at 8:18 am |
    • Edward

      You already have gills. Well, evolved gills anyhow

      February 2, 2013 at 11:47 am |
      • ken

        LOl you fool

        February 2, 2013 at 1:34 pm |
  32. Thomas

    Life found a way.

    February 2, 2013 at 8:01 am |
    • KhakiSacChampion

      I see what you did there. Goldbloom for life.

      February 2, 2013 at 4:49 pm |
  33. Ken

    Crappy article God gave it the ability to change.

    February 2, 2013 at 6:41 am |
    • James

      Wow. Did you read the article?

      February 2, 2013 at 7:05 am |
    • Mario

      You're an idi*t.

      February 2, 2013 at 7:05 am |
      • ken

        up yours

        February 2, 2013 at 1:35 pm |
    • Ed Schultz

      I agree, if you can prove that god exists. If you can't, then you are no smarter than the lie of "macro evolution".

      February 2, 2013 at 8:44 am |
      • Jeff S

        Noe @ed, surely you went to college and took evolution. Macrosevolution is just evolution happening over a longer period of time. Extinction is considered a pattern of macroevolution. Are you saying that we can prove that species that once lived here are no longer here?

        We see species adapting over smaller periods of time. Adaption is a mechanism of evolution. Since we can see adaption working we know evolution is working. If that adaption we see happens over a period of millions of years than we macroevolution. Heck Humans have evolved. We have organs we no longer use as part of that adaption. I don't see how people can say evolution is a lie. We see it happening. Or at least those of us willing to look at something without prejudice.

        February 2, 2013 at 9:36 am |
      • Paul

        Antibiotic resistant bacteria... evolution proven.

        February 2, 2013 at 12:09 pm |
    • Anon

      Ken is able to change his name...god is powerful...on the 8th day he stole Al Gore's credit for inventing the internet. (I love how word of mouth gets distorted when it enters mass and the holy ghost chat about it all the time)

      February 2, 2013 at 9:02 am |
    • KhakiSacChampion

      What a cop out.

      February 2, 2013 at 4:57 pm |
  34. Mark

    They should call it it Michael Jackson fish.

    February 2, 2013 at 6:36 am |
  35. mmi16

    And humans get hung up on the gay-straight conundrum!

    February 2, 2013 at 6:15 am |
    • Patines

      It's just in public environment. Behind the doors everything goes.

      February 2, 2013 at 3:27 pm |
      • DarthSidious

        lol... Behind closed doors. The 1950's called.

        February 2, 2013 at 7:36 pm |


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