Anemonefish clownfish Nemo

The amazing life of clownfish – and a twist ‘Finding Nemo’ missed

You can call them clownfish, you can call them anemonefish but the world probably now knows them best as….Nemos.

Thanks to Pixar and their blockbuster film from 2003, these much-loved creatures have become one of the most popular sights in the underwater world and are a delight to divers who come across them.

However, had the makers accurately followed nature’s work, the film could have had a very interesting twist.

These vibrant fish, with their distinctive orange, white, and black stripes, inhabit the warm waters of all Emperor Divers’ destinations – the Indian and Pacific Oceans and the Red Sea. They belong to the subfamily Amphiprioninae in the family Pomacentridae and are famous for their symbiotic relationship with sea anemones.

Typically about 4.3 inches in length, the largest species reach up to 7 inches. Their bright colouration serves as a warning to predators about their poisonous habitat—the sea anemone. The mucus on their skin provides immunity to the anemone’s stinging tentacles, allowing them to live safely among them. This symbiosis benefits both parties: clownfish receive protection from predators (although not necessarily enough to deter hungry barracuda!), while anemones gain nourishment from the nutrients in the clownfish’s waste.


Clownfish are omnivorous, feeding on algae, zooplankton, and small crustaceans. They are also known to eat the dead tentacles of their host anemone, contributing to the cleanliness of their environment. Socially, clownfish live in groups within a single anemone, consisting of a dominant female, a male mate, and several subordinate males. This hierarchy is maintained through aggressive behaviours, with the dominant female being the largest and most assertive.

And this is where Pixar might have got it wrong.

Clownfish exhibit a fascinating reproductive strategy known as protandry, where all individuals are born male, and the dominant male changes sex to female when the previous female dies.

This means in real life Nemo’s dad, Marlin, would have become his mum if the story followed the species’ natural biology.

In a typical clownfish group, there is a strict social hierarchy. The largest and most dominant individual is the female, the second-largest is her male mate, and the rest are smaller, non-breeding males. If the dominant female dies, the dominant male undergoes a sex change and becomes the new female. The largest of the non-breeding males then matures into the breeding male.

Given this biological framework, if Nemo’s mother had died in real life, Marlin, as the male, would have transitioned to become the female. A new dominant male from the non-breeding males would then become Nemo’s new father. This remarkable adaptive strategy ensures the continuity and stability of the clownfish population.

The breeding pair will engage in a courtship ritual involving dancing and fin displays before the female lays her eggs on a flat surface near the anemone. The male then fertilises the eggs and takes on the primary role of guarding and aerating them until they hatch.

The larvae, once hatched, drift in the open ocean for about 10-12 days before settling on the reef and finding a suitable anemone to inhabit. This process ensures the dispersion of the species across a wide area.

And so clownfish continue to fascinate the world and enthral divers.

A remarkable example of marine biodiversity, showcasing unique adaptations and behaviours that intrigue scientists. Their symbiotic relationship with sea anemones highlights the intricate balance of marine ecosystems and underscores the importance of conservation efforts to preserve these vibrant underwater communities.

A little bit of Hollywood adaptation is, of course, fully understandable. However, the knock-on effect of global attention has been both a benefit and a curse.

The popularity of Finding Nemo led to a marked increase in people’s interest in marine conservation. However, it also brought challenges as the demand for clownfish in the aquarium trade surged, sometimes leading to overfishing.

As most divers will tell you, the best place for fish is in the ocean not a tank – or possibly on a big screen!


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