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Secret sex life of a clownfish

Harald Franzen
June 29, 2017

"Finding Nemo" delivered the little clownfish into the collective consciousness with an almighty splash, but it didn't divulge their reproductive quirks.

Clown fish
Image: imago/OceanPhoto

Everyone loves Nemo and his overprotective dad Marlin, the clownfish duo from the Great Barrier Reef comically immortalized in two animated blockbuster movies. In the first, following the death of his wife, Marlin is left to raise his adventurous son Nemo as a single dad, surviving unthinkable dangers to find him when he goes missing. Had it been a real-life story of a clownfish, it would likely have had an even more unimaginable twist.

Clownfish are monogamous, that much is true, but out in the wild, they don't have the luxury of turning an anemone into a private single-family home. In fact, because the little orange and white fish rely on the toxic tentacled sea creatures for the shelter they need to survive, it can get quite crowded inside. As a result, there is a strict hierarchy in place and the only ones who get to breed are the dominant couple.

It gets really interesting when the boss, aka the dominant female, dies. Because clownfish are so-called sequential hermaphrodites - they can, having started life as males, become females as they mature.

So when the she-boss departs this mortal coil, the dominant male steps into the breech. Not by becoming a single dad, but by becoming a female. The new mother. His place is taken by the largest remaining juvenile. And they can then mate, thus ensuring the continued circle of life. Seems like Marlin got off easy.

three clown fish
The younger clown fish do not get the chance to reproduceImage: Colourbox.com