Anemonefish – Knowing Nemo

Anemonefish – Knowing Nemo
A movie star …

Since “Finding Nemo” was flickering across the screens, almost everybody knows anemonefish. But unfortunately few people are aware of Nemo’s real life or his biology.

As divers, we love the cute bright orange fish with the white stripes because he likes to interact with us in a funny way (not that funny from his perspective) and makes a popular photographic model since he never stays far away from his anemone.

We also know that the anemone protects him and sometimes it seems like a whole family of these fish is living there with bigger and smaller individuals at the same spot.

The truth is that Nemo’s real life is even more interesting and exciting than the actual movie.
The Red Sea Nemo and his anemone

The two-band anemonefish (Amphiprion bictinctus) is the biggest of all known anemonefish with a size up to 14 cm. It belongs to the damselfishes and has a life expectancy of 6 – 10 years in the wild.

As we know Nemo is living in a symbiosis with different species of sea anemones (6 different types in the Red Sea). The fish protects the anemone against predators such as butterfly fish, eats parasites and causes an increased water and therefore nutrient circulation within the sea anemone. On the other hand, Nemo also gets protection from the anemone since their stings are capable of killing small fish instantly. Moreover scientists found that the fish are suffering from less parasites when living in sea anemones.

Therefore the relationship of sea anemones and anemonefish is mutualistic: They protect each other and gain benefits (increased survival chance and health/fitness) from their association.

The interesting life cycle of Nemo

Keep your eyes open when you find an anemone during your next dive! Quite often you may find a nest full of eggs on a hard substrate next to the host anemone. Are the eggs appearing in a red colour the larvae are not yet developed and the female anemonefish recently placed them on the substrate. If the eggs appear silvery the larvae are close to hatching. Have a closer look then (if your buoyancy skills allow) and you might even see the eyes of the baby Nemos within the eggs.

Unlike many other coral reef fish species the anemonefish parents take care of their eggs, fanning them with their fins to provide more oxygen flow and remove algae from them. But now we’re coming to the really interesting part almost nobody knows about Nemo. After hatching all larvae fish are males and they don’t stay with their parents but go unprotected to the open water where they’re drifting with the currents.

After they developed to small juvenile anemonefish they locate the reef through sound and taste. But uninhabited sea anemones are rare so they mostly have to share it with an adult pair of anemonefish and/or other juveniles. Nemo’s young life is very hard and stressful. After finding a host anemone he needs to overcome the stinging and acclimate that can last for several hours.

As juvenile he’s also the lowest in the hierarchy and he’ll first don’t get the chance to grow or even reproduce. There’s only one reproducing adult pair per sea anemone where the largest fish is the female and the second largest her male partner. The growth of the other anemonefish is inhibited by that pair. The years of waiting begin and Nemo moves up the hierarchy if an older animal dies. If he’s lucky, he can take over the position of the dominant male and will be able to reproduce with the dominant female.

But the ladder of success – who would have guessed – is reached when Nemo finally becomes a woman. This happens when the dominant female passes away. Then the dominant male reverses his sex and turns into the reproducing female.

The tiny star of the Red Sea coral reefs

As you can see, the anemonefish is not only a gorgeous fish but also a very interesting species of the Red Sea fauna. Take your knowledge with you underwater and keep observing these cute fish. You will find then on most of Dahab’s dive sites!

We’re sure during your next dive you’ll see anemonefish and their beautiful homes with different eyes.

• Title photo: Juergen Donauer
• All other photos: Christian Alter