transgender fish

Surprisingly, transgender fish do exist and in fact around 2% of all fish species are able to change biological sex! 

Species of fish that are able to change biological sex, i.e. transgender fish, are said to be ‘sexually labile’. Some of you reading this with a particular interest in fish biology may already have an example in mind. For those of you who don’t, let me give you perhaps the most well known case of a species of transgender fish!


Transgender fish number 1 : clownfish


Schools of clownfish (they’re not studying, that’s just the name for a group) are organised into hierarchical structures. At the very top of this hierarchy is the female, the largest and most dominant clownfish in the school. Then, there is one male who takes up the role of ‘breeding male’ and is the second largest of the group. Then there are several other non-breeding males who are organised down the hierarchy based on their size. There’s a joke to be made there but i like to think i’m better than that.

transgender fish

The breeding process of the clownfish goes as follows. The female, or leader of the group, lays a very large clutch of eggs. This can range from 100 to 1500 depending on her size (imagine having 1500 kids???). Then, the dominant male (otherwise known as the breeding male) plays his part. This means he fertilizes the eggs. Then, with time, the eggs hatch and there are hundreds of new little Nemo’s swimming around!

You may be wondering, what happens if the female dies since there’s only one of them? A very good question indeed, and one with a remarkable answer.

When a female clownfish dies, the most dominant male changes sex and takes her place! Isn’t that amazing!

In case you’re wondering how this works, let me give you a run down. Male clownfish has fully functional testes (a male reproductive organ) much like males of almost every other species on earth. However, they also possess latent cells that can become ovaries (a female reproductive organ) under the right conditions. If you were unsure as to the meaning of ‘latent’ it literally just means existing, but not yet developed.

transgender fish

When the female clownfish dies, the most dominant male’s testes degenerate and the latent cells grow to form fully functional ovaries!

Hopefully i haven’t changed the way you’ll see Finding Nemo forever with this amazing fact! because, think about it. Nemo’s mother died meaning that his dad, good old Marlon, probably became a female to take her place. Something to consider next time you give it a watch.

Other transgender fish

Of course, clownfish aren’t the only species of transgender fish.

Young male moray eels are born jet black with a thin yellow line down their back. They later turn a beautiful electric blue, before eventually becoming bright yellow… and female! They gain the ability to lay eggs and can even do this sooner to aid the survival of the species.

transgender fish

Some species of fish actually possess male and female sex organs at the same time. These species are quite aptly named simultaneous hermaphrodites, a very fitting name indeed.

I encourage you to research this topic more, there’s plenty more to be learned!


Extra information


Animal-Club provides animal parties or animal handling workshops. You will be able to see, learn and interact with many wonderful animals with the help of our presenters. Our mobile zoo has many friendly animals such as rabbits, tarantulas, geckos, vinegaroons and more, perfect for an animal party. We can also come over to your school for an animal school visit or arrange for an animal workshop with us where the children can learn about looking after animals and animal behaviour, and have fun too.