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Kobudai and California Sheephead Fish: Facts and Gender Change

Linda Crampton is a writer and experienced science teacher with an honors degree in biology. She enjoys writing about science and nature.

Some people have noticed that the face of a kobudai can look somewhat like that of a human, despite the bulging forehead.

Some people have noticed that the face of a kobudai can look somewhat like that of a human, despite the bulging forehead.

Interesting Relatives in the Wrasse Family

The Asian sheepshead wrasse (Semicossyphus reticulatus) has an unusual appearance. Both genders have a bulbous forehead, but the male’s forehead can be huge. The fish may change gender during its life. It lives in the water around Japan, China, and Korea. In Japan, it’s known as the kobudai.

The California sheephead (Semicossyphus pulcher) is a colorful animal that can be found from Monterey Bay to the Sea of Cortez. The male has a slightly bulbous forehead. The animal has the ability to change its gender, like its relative described above. It has large canine teeth that sometimes protrude from its mouth.

Animals in the genus Semicossyphus belong to the wrasse family, or the Labridae. Other members of the family and some fish in other families can also change their gender. They develop the reproductive organs, external features, and behavior of the opposite sex. Some species of fish do this multiple times in their life.

A kobudai with slightly different coloration

A kobudai with slightly different coloration

Asian Sheepshead Wrasse or Kobudai

The Asian sheepshead wrasse is usually seen in areas with rocky reefs. The fish may be as long as thirty-nine inches but is usually shorter. Its color ranges from very pale pink to brown. It has a large chin as well as a bump on its forehead. The wrasse feeds on shellfish and on crustaceans such as crabs.

The International Union for Conservation of Nature or IUCN says that "remarkably little information" is known about the fish considering it's large, has conspicuous features, and is caught for food. The document was written in 2004 and hasn't been updated. The population status of the animal is listed as "Data Deficient".

Yoriko, the kobudai described below, is probably an exception to the generalization that little is known about the species. She has been observed for over thirty years and has become locally famous.

A Famous Kobudai Named Yoriko

An Introduction to Yoriko

Yoriko lives in Hasama Underwater Park in Japan and is referred to as "she". I'll follow this tradition. I've seen photos of kobudai with multiple variations in the size of their forehead knob and chin. The features probably depend on the animal's age as well as its sex. I don't like to identify the gender of a particular fish (except in extreme circumstances) unless this has been confirmed by a kobudai expert.

Around thirty years ago, a scuba diver named Hiroyuki Arakawa discovered that Yoriko was injured and couldn't catch her own food. He brought her crabs to eat every day until she recovered. The pair bonded during this activity.

Hasama Underwater Park

Based on the photos that I've seen, the park where Yuriko lives is open to the surrounding water, so she's free to come and go. The fish in the park should be safe from human hunters as long as they don't leave the area.

Hiroyuki visits the park regularly in order to maintain the underwater Shinto shrine that is located there. Yoriko lives near the gates of the shrine. The diver strikes the metal gates when he arrives to attract the attention of the fish. He and Yoriko often meet when he does this and have done so since the diver rescued her.

An Interspecies Friendship

The fish appears to appreciate the meetings with her friend and allows him and certain other people to touch her. She allows only Hiroyuki to kiss her, however. The idea of a fish having a friend may sound strange to some people. Scientists are discovering that at least some species of fish are more intelligent than we realized, however.

A Confident and Friendly Fish

The video above is longer than the first one but gives a good idea of the nature of Hasama Underwater Park and its inhabitants. Yoriko plays a starring role in the video, especially in the first part. She's shown by the shrine in the video screen above.

At one point in the video, Yoriko is so confident and perhaps so interested in what Hiroyuki is dislodging from the shrine that he has to gently push her away several times so that she doesn't get hit by his hammer.

Gender Change in the Kobudai

The IUCN says that it's unknown whether an Asian sheepshead wrasse can change its gender. As mentioned above, its report was written a long time ago. Two more recent studies suggest that the gender of the fish can change, but only from a female to a male. A transformed female has testes, a very large and bulbous forehead, a big lower jaw, and a more aggressive nature.

The BBC series Blue Planet ll has filmed transition stages between females and males in Japan. The producer of the series says that the change from a female to a male takes months and that it was impossible for the team to film a single female during her entire transition. Instead, during two seasons they filmed multiple fish that were in different stages in their transition. This enabled them to create a timeline of events in the transition.

I haven't watched the Blue Planet series so I can't give my personal opinion about the value of the process described above. The process sounds logical, but I do have some questions about it. I wonder whether specific individuals were identified and followed as they changed gender during a season and whether a normal variation in some fish could have been mistaken for a transition stage.

The second reference from the BBC below suggests that in at least one case the film team did follow the change in a particular fish. The article mentions a ten-year-old female that changed into a male with "a huge bulbous forehead". After her sex change, the fish defeated the aging male that she had previously mated with and became dominant herself (or more accurately, himself).

By filming multiple individuals at different stages, over two seasons of observation, we were able to reveal the entire story of the incredible transformation as a female changes sex to become a male.

— Jonathan Smith, Producer of Blue Planet ll, with reference to the kobudai

A Diving Instructor's Observations

According to an article written by a diver and photographer on the Dive Photo Guide website, a diving instructor in Japan named Yoshifumi Aihoshi says that he's observed a kobudai named Kinjiro for eighteen years. The fish was once a female. After she had reached maturity, she changed into a male over a period of several months.

The writer of the article says that Aihoshi has an "in-depth knowledge of the species." The diving instructor was frequently in the area where Kinjiro lived and recognized her. He was able to watch the change in her body over time.

In some fish species that can change gender, nearly all the animals appear to do so. It can't be said with certainty that all the individuals in the species change their gender, however.

Features and Life of the California Sheephead

More is known about the California sheephead than the Asian sheepshead wrasse, perhaps because the Californian animals are popular food fish in the United States. The fish may reach up to three feet in length. Males are larger than females. The males, females, and juveniles look different from one another.

  • Mature males have red eyes, a black, dark blue, or brown head and tail, an orange or partially orange middle section, and a white chin. The males have a bulge on their forehead, though it's nowhere near as large as that of a male kobudai. The females lack the bulge.
  • Mature females are pink with orange highlights and a white undersurface.
  • The young sheephead is bright orange in color with a horizontal white line along each side. It has black spots on its fins.

The animals live in kelp forests and by rocky reefs. They hunt during the day and hide at night. Most of their prey are covered with hard shells and are attached to rocks. The strong teeth of the fish enable the animals to detach the prey from rocks. Sea urchins, crabs, and lobsters are some of the prey types that are eaten. The fish has a throat plate made of modified bones that crush the prey into smaller pieces after the teeth have dealt with it.

At night, the California sheephead finds a crevice in a rock in which it can hide and sleep. It secretes a mucus cocoon, which prevents predators from detecting its scent.

A female California sheephead

A female California sheephead

Reproduction, Lifespan, and Status

The mating season of the California sheephead lasts from July to September. A single male establishes a mating territory and mates with several females during this time. He's said to have a harem. The male leads a female in a circle. He deposits sperm, and then the female deposits eggs over the sperm. The female may lay thousands of eggs in one day. The eggs hatch into larvae, which then develop into adults (if they're not eaten by predators).

Like its Asian relative, the California sheephead is potentially a very long-lived animal. According to the University of California, San Diego, one animal died at the age of 53, which is the current record for a wild member of the species. Unfortunately, some fish don't get the opportunity to live this long due to fishing activities.

The IUCN Red List classifies the animal's population as 'Vulnerable" and says that its numbers are decreasing. Once again, this is based on an old assessment. It was performed in 2006. Other sources are concerned about the population size of the species today, however. The fish is eaten by seals and sea lions as well as humans.

A juvenile California sheephead

A juvenile California sheephead

All sheephead are born female and can develop into males when the ratio of males to females becomes imbalanced in a local population.

— Monterey Bay Aquarium

Gender Change in California Sheepheads

Gender change is quite common in fish. There are still many unanswered questions about the process, but it appears to have developed because it's beneficial for the local population of the species in some way. The ability of the California sheephead to change gender has been confirmed by scientists. The age at which a female changes into a male (if she actually does this) seems to vary considerably, however.

One stimulus for the change is stress in the composition of the population. Researchers have found that if a dominant male in a mating territory dies, a female in the area will become a male and replace him. The fish also change gender in other situations when the male to female ratio is not ideal in a population.

It has been suggested that if males are preferentially caught for food because they are bigger, females may be able to replace them by changing gender. Discovering whether this is actually the case requires more study.

Being able to switch sex maximises the chances of passing on genes if environmental or social circumstances should change.

— Zoe Cormier, via the BBC blog

Facts About Gender Change in Fish


Some gender-changing fish begins their lives as females while others begin as males. Fish that are female first and then become male (such as the two species highlighted in this article) are said to be protogynous. Those that are male first and then become a female are classified as protandrous. Both types of fish are also known as sequential hermaphrodites.

Reproductive Structures

The change in gender is fish not completely understood yet, but some facts have been discovered. Research suggests that in at least some gender-changing fish, male and female reproductive organs and tissue are present at the same time. One type may be inactivated while the other is active or one type may be present in an immature form while the other type is mature. As the gender of the fish changes in the latter case, the immature structures of the opposite gender mature and the previously used ones are inactivated. In the wrasse described below, the change goes a step further. An ovary is completely transformed into a testis during the sex change.

Sex Change in the Bluehead Wrasse

Though the bluehead wrasse (Thalassoma bifasciatum) belongs to a different genus from the two species described above, it's a member of the same family. It's a smaller animal than the other two species and lives for a much shorter time, but it does change gender. It lives in reefs of the Caribbean. Some interesting discoveries have been made in the species that may apply to the other two.

When the male bluehead wrasse is removed from the harem, the biggest female becomes a male. Genes that direct the production of estrogen (the female hormone) are inactivated, and genes that direct the production of androgens (male hormones) are activated. Other genes related to female features are turned off, and ones that are related to male characteristics are turned on. Researchers have also discovered that genes that can change differentiated cells back into the unspecialized cells characteristic of an embryo become active. The animal's ovaries are converted into testes during the changes.

If (the) male is removed from the group, something extraordinary happens: the largest female in the group changes sex to become male. Her behaviour changes within minutes. Within ten days, her ovaries transform into sperm-producing testes. Within 21 days she appears completely male.

— Jenny Graves et al, via The Conversation, with respect to the bluehead wrasse

Triggers for Gender Change

The cells of fish contain chromosomes, as ours do. In addition, as in us the chromosomes of fish contain genes that determine many of an individual's characteristics. While we have two sex chromosomes that determine gender, the situation is not as simple in fish. (Even in us, the situation is sometimes not as simple as it appears.)

Gender imbalance in a group can cause a sex change in one or more fish, as described above. Water temperature is another factor that controls gender in at least some species of fish. Chemicals that are produced in an animal (such as hormones and enzymes) play an important role in the sex changes. The pH of the water and the identity of chemicals that enter the fish from the environment might influence gender as well.

Though some of the triggers for gender change are known or suspected, a detailed description about what happens in an animal's body after a trigger appears requires more research. The study could be very educational.

Fascinating Fish

The ability of the Asian sheepshead wrasse and the California sheephead to change gender is intriguing. There is probably a lot more to discover about both of these species and about the triggers for change in gender in fish. Learning more about the factors involved in the change (preferably without harming the animals) would likely be very interesting.

The undersea world still holds many mysteries. The diverse organisms that live there and the influence of their environment on their lives are fascinating to explore. Understanding more about marine life might be useful for us as well as interesting.


This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on December 04, 2020:

Thank you, Devika. I always appreciate your visits.

Devika Primić from Dubrovnik, Croatia on December 04, 2020:

AliciaC A great write up here and with your knowledge, it enlightens us about something different and interesting. Thank you for this fascinating hub.

Linda Crampton (author) from British Columbia, Canada on December 04, 2020:

Hi. The gender change is a natural process. Nature can be very interesting!

Brinafr3sh from West Coast, United States on December 04, 2020:

Hi Alicia, this is too interesting and strange fish. Have the Japanese kobudai fish been genetically modified to change gender or have they always been that way? Thanks

Linda Crampton (author) from British Columbia, Canada on November 26, 2020:

Thank you very much, Devika.

Devika Primić from Dubrovnik, Croatia on November 26, 2020:

AliciaC Great writing about nature the world has to offer. Beautiful and most fascinating.

Linda Crampton (author) from British Columbia, Canada on November 25, 2020:

Hi, Denise. Thank you very much for commenting. The world of nature is certainly amazing!

I hope you have a very enjoyable Thanksgiving. Blessings to you.

Denise McGill from Fresno CA on November 25, 2020:

That is incredible. Isn't it amazing how much there still is to learn in the world? I am never ceased to be amazed.

Happy Thanksgiving.



Linda Crampton (author) from British Columbia, Canada on November 23, 2020:

Thanks for the visit, Adrienne. I think it's an interesting fish, too!

Adrienne Farricelli on November 23, 2020:

What an interesting fish! I never heard about kobudai before. Thanks for sharing such interesting information. I liked watching the videos.

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Hi, Linda. Public aquariums can be interesting and educational places, though I think it's important that the animals there have a satisfactory habitat and life. The Vancouver Aquarium (the nearest one to my home) is closed at the moment due to the coronavirus situation. I hope it's able to open again soon.

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Thank you very much, Bill. I hope the rest of the weekend is enjoyable for you.

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Thank you, Fran. Nature shows can be very interesting. There is so much to learn about living things!

Linda Chechar from Arizona on November 22, 2020:

These are odd fish that change their genders. I lived in La Jolla and I always enjoyed the aquarium. I did see those sheepheads!

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Thank you very much, Peggy. I wish more people considered the sentience of other animals. I think it's an important topic.

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Hi, Eric. Thank you for commenting. I like the friendship part, too. It's interesting that the relationship has lasted for so long.

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

I appreciate your comment, Pamela. I often discover new facts about fish that surprise me. I think it's sad that some people only think of them as food. They are interesting organisms.

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Hi, Dora. Thank you for the comment. There are some amazing sights in the ocean! I hope you're having a good weekend.

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Hi, Bill. The ocean is a very interesting place. There seems to be so much to learn about it. The relationship between the man and the fish is fascinating, as you say. I appreciate your comment.

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Hi, Nithya. Thanks for the visit, I hope the fish survive for a long time to come.

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Thank you for the visit and for sharing the interesting story, Manatita. I agree with the idea in your last paragraph. I hope you have a good Sunday.

Bill Holland from Olympia, WA on November 22, 2020:

Excellent as always, once I found it so I could read it. It was worth the wait, and I appreciate the efforts you make in researching. Well done, Linda!

Linda Crampton (author) from British Columbia, Canada on November 22, 2020:

Hi, John. I think it's quite a remarkable fish, too. There are a lot of interesting sights in the ocean! Thank you for the comment.

fran rooks from Toledo, Ohio on November 22, 2020:

Excellent article. One of my favorite programs is Planet Earth and Blue Planet. The fish is almost sad looking. I love the fact Toriko takes such good care of his 'friend'. Thanks so much for your article.

Peggy Woods from Houston, Texas on November 22, 2020:

Your article about the Kodudai and the wrasse fish is fascinating! That one who became a pet of sorts at the underwater shrine makes a sweet story. It proves (at least to me) that all animal species are sentient beings and have feelings. I loved reading this article! Yours are always so informative.

Eric Dierker from Spring Valley, CA. U.S.A. on November 22, 2020:

How very interesting. Thank you for this, I may never have known. I liked the friendship part the most.

Pamela Oglesby from Sunny Florida on November 22, 2020:

I knew almost nothing about the sheephead until now. This is a very well-written article with a wealth of information, Linda. The videos were interesting as well. I never thought about a fish finding a safe place to sleep.I also thought the sex change information was interesting.

Dora Weithers from The Caribbean on November 22, 2020:

The uniqueness of the sheephead is in a mysterious class all by itself. With features that are almost human and its ability to change genders, it is an amazing creature. Thanks again for bringing us the facts on such awesome specimen.

Bill De Giulio from Massachusetts on November 22, 2020:

What an amazing species. I was not familiar with the kobudai or the California sheepshead. The relationship between Yoriko and Hiroyuki is fascinating and I really enjoyed the videos of them interacting. I was not aware that some fish species exhibit gender change, amazing. Great job, Linda. This is another educational article and proves that we have so much to learn about our oceans and the creatures that live there.

Nithya Venkat from Dubai on November 22, 2020:

An interesting and informative article about the Kobudai and the California Sheephead. I hope that these fishes do not become extinct before we get to know about them.

manatita44 from london on November 22, 2020:

I found the videos of the underwater Park and Kobudai of Japan most interesting. It is a very clever fish.

I'm reminded of King Bharata who was on the verge of enlightenment. He saved a fawn of a pregnant deer who died giving birth, while jumping across a river. The King nursed it to health and gradually became so attached to it, that when he died, he became a deer.

This deer, however, was quite clever and always visited spiritual retreats and stayed around Saints all its life. So your fish seems to like shrines and good men. Similar thing. Haha.

Great seeing the different species and leaning of their ability to change sex and yes, there is a tiny bit of the human appearance visible.

Not wanting to push you this Sunday morning, but the mystic says that it is God in all things, or you might say that all things, sentient and non-sentient, are a spark of the Divine. Very informative article and I'm glad I caught you before the Niche site takes over. Peace.

John Hansen from Australia (Gondwana Land) on November 22, 2020:

What an interesting article and wonderful videos. Quite a remarkable fish. Thank you for sharing, Linda.

Linda Crampton (author) from British Columbia, Canada on November 21, 2020:

Thank you very much, Liz. I appreciate your visit and your comment.

Liz Westwood from UK on November 21, 2020:

This is an excellent article. It is well-researched and well-illustrated. The Blue Planet was very popular in the UK. I was intrigued by Hasama inderwater park and the relationship between Hiroyuki and Yoriko. The concept of sex-changing fish is new to me too.