What Finding Nemo didn’t tell you about fish sex


Blue Planet II, the BBC’s latest flagship nature documentary is almost open us, and the press is currently awash with teaser stories and clips.

This week, the Daily Mail, the bastion of British conservative reactionary values, ran a story revealing that Blue Planet II will include footage of a fish changing sex.

The fish in question is the delightful Asian sheepshead wrasse.

Semicossyphus reticulatus
What a beauty

Whilst another species of sheepshead wrasse is known to change sex, with some females becoming males, it wasn’t known if the Asian sheepshead wrasse did so too.

Well apparently it does, and the BBC have it on film.

Fish sex as a liberal BBC plot?

That some fish change sex, called sequential hermaphroditism, is not news, it’s been reported in around 2% of bony fishes.

However, this was news to a proportion of the Daily Mail’s readership, and some didn’t react well. The comments section under the story contains some absolute gems, with some of the best collated by the DM reporter.

Many readers questioned the science, interpreting the story as nothing more than a liberal, left wing, BBC plot to shove transgender-accepting values down their throats.

We need to talk about fish sex

It’s easy to laugh at this, and I have, but it’s depressing too. It’s painful seeing people deny elements of the natural world because they feel they challenge their worldview (never mind that a worldview without gender fluidity is a very silly worldview).

So maybe we need to talk more about fish sex?

Not because it’s fun to shock prudes (even though it is), but because it’s interesting, and I think it will help people engage more with the natural world.

I also think that the more you learn about the natural world, the more you realise you can’t impinge your own values on it, and that you shouldn’t try to derive your values from it either.

Clownfish are probably a good place to begin.


Thanks to the Finding Nemo films, clownfish are a loved species, you’ll regularly hear children and adults pointing at them in aquariums and excitedly shouting “Nemo!”

But I suspect few people know that clownfish change sex too.

Nemo, I am your father… but also your mother.

In many clownfish species, fish are born male, but may become female later in life.

Clownfish usually live in groups with a dominance hierarchy. The top male becomes the female, and she forms a mating pair with the number two male. The other males in the group don’t get to mate.

If the female dies or leaves, the top male becomes the new female, and the other males move one step up the hierarchy.

So if Finding Nemo was more scientifically accurate, Nemo’s father would have become his mother. And Nemo, as the only other male in the group, would have fertilised his father/mother’s eggs.

Imagine that as a Disney film.

Enough, get to the point.

Sex in the natural world isn’t as fixed as many Daily Mail readers would like it to be, and sex-changing fish are not agents of liberal BBC propaganda. We can fight this sort of nonsense by talking more about fish sex.

Also, moralising from nature is ludicrous.

Just because something happens in the natural world doesn’t make it right or wrong for us. Nature doesn’t stop to consider the implications of evolution and ecology, because it can’t, because nature isn’t a person.

That fish change their sex should have no bearing on your own views of human sexuality – remember the scientifically accurate version of Finding Nemo.

Thanks to Anna Phillips for inspiring this post via twitter fun!

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