The Nemo Factor

Nemo, the animated film star, is now part of popular culture. But what is it about its real-life counterpart that turned this little fish so readily into a Hollywood icon? Sarah Curran finds anemonefish as fascinating as they are frustrating

IT HAPPENED ON AN UNPRECEDENTED SCALE, almost overnight. After the movie, it seems it is no longer possible for a diver to see or photograph an anemonefish without referring to it as Nemo. Similarities are quick to be drawn, too. 'He even had a little fin like Nemo,' Ken, a 45-year-old doctor, said to me, every bit as animated as his cartoon hero. No longer were the cute critters called 'it', but each was assigned a gender. 'He had his dad with him,' continued Ken, scrolling through the pictures on his camera, stopping on appropriate images for them to be cooed over. The hero of the animated wildlife extravaganza Finding Nemo is enshrined in popular dive culture for the foreseeable future. The world's smallest screen idol has become so popular that it is now an official emblem of Queensland in Australia. This is surely an unprecedented rise for any species. But Nemo's eccentric odyssey made me take another look at a fish that is such an intrinsic part of divers' reef experience. Beyond poking fingers into anemones to watch the little fish work itself up into a frenzy of territoriality, few divers take time to understand the creature. The anemonefish was first described in 1869. It is often called the clownfish, but in fact only two of the many varieties of anemonefish can legitimately be referred to as 'clown'. The red-and-white-striped 'clown anemonefish' and, surprisingly, the 'false clown anemonefish', are the cause of this naming confusion, which arises in part because these more jovial names are used in the aquarium trade. The fish bounce and bumble around in their clownish clothing and it seems appropriate to use the term for a fish that makes us smile. But clownfish are anemonefish and belong to the same scientific genus. Whatever we call them, anemonefish have always fascinated, charmed and frustrated us. The fascinating kind were those whose pictures Ken had shown us on the boat; the charming are the ones Queensland has shown the world; and the frustrating I experienced recently as I waited desperately for two examples to stay within the frame of my camera. I'd just get them lined up and, click - one more shot of an empty anemone, or of a tiny orange blaze in one corner. Anemonefish fascinate us because of their unique collaboration with a different species. The word 'symbiosis' describes the true partnership nature of the relationship, but its literal translation 'living together' tells little of the benefits or disadvantages for either party. Twenty-eight species of anemonefish use anemones as hosts but, of 1000 species of anemone, only 10 play hostto anemonefish, and all are found in tropical waters. Anemones are related to corals and jellyfish and carry the same nematocysts - tiny, lethal harpoons capable of inflicting pain on fish and, as many divers can testify, humans too. So how do the fish survive in what is essentially a hostile environment, and a death-trap for other fish? The movie made much in its early scenes of Nemo's dad swimming in and out of anemone tentacles. This rapid movement, cute though it is, is essentially functional. The fish are smearing mucous from the anemone onto their skin to give them a protective chemical camouflage, and the constant contact with the anemone maintains this covering. Research shows that, after extended periods away, the fish will get stung on their return. There are also suggestions that they have evolved their own mucous so that it lacks the components that stimulate the fatal nematocysts. Like most things in nature, it's probably a bit of both. Either way, that's one hell of an advanced and sneaky defence system; dressing yourself up like the enemy and then evolving skin that doesn't react to missiles. Anemonefish are never found without an anemone host in the wild, but haven't we all seen anemonefish in aquaria seemingly as happy as, well, Nemo? It appears that they can survive without their hosts in captivity, but take away the anemone in the wild, and they quickly become vulnerable to larger predators. Would you believe that fish could be poor swimmers? Well, our candy-striped friends are just that, making them easy prey. So not only do they require the protection of the host, but they also lay their eggs under the oral disc (mouth area) of the anemone, where the male tends to them. And there may be other, less obvious, ways in which the fish benefits from the anemone host. Captive fish tend to bask in the bubbles of filter systems or in the fronds of aquarium vegetation, so they may just feel good to be among the anemone's tentacles. My dive buddy Paddy sat staring at a little Amphiprion clarkii, frantically defending his host from my camera and Paddy's mask. I refused to accept defeat as he bobbed in and out at breakneck speed. But looking around, I realised that, although the entire reef before me was carpeted in anemones, I could not see one without a little red-and-white fish dancing around in its tentacles. I understood that the fish needed the host, but just what did the anemone get out of the relationship? The advantages for anemones are not obvious. The fish don't seem to harm them in any way, but is this a one-sided relationship? The fact that anemones are found thriving with our little friends suggests not, and research has shown that, for some anemones at least, being deprived of their guests means that they become prey to other hunters on the reef, such as butterflyfish. The fish eat parasites that infect anemones, and increase water circulation, as well as keeping other fish away. In return, the anemone stings any other predators that come near the little fish. I watched Ken poking his finger into an anemone to entice the fish out for a photo-shoot. It darted in and out and came up to his mask, inquisitive and at the same time defensive. Ken giggled with glee. It is this interaction that we find so charming, this and the childlike swim-waddle as anemonefish try to get back to the safety of their host. Anemonefish display what seem to us to be human characteristics: they appear curious, protective, have a 'home', couples mate and stay together, sometimes for years. The males tend to the eggs, wafting their tiny fins to clear the nest of debris, which endears them to emancipated women and new men. Domesticated men - what a blessing, defending the marital home and also looking after the little ones! One of the strangest things about anemonefish, one not highlighted in the movie, is that they change sex. But it's not the traditional female-to-male thing found in most fish. For gender-bending fish desperate to get in touch with their feminine urges, being an anemonefish is the right choice. 'Protandrous hermaphroditism' will come up in a bar quiz one of these days, so pay attention! The largest and socially dominant fish in an anemone is the female. She has functioning ovaries with remnants of male gonads. The smaller male may be less than half the size of the female, and has functioning testes but also non-functioning female sex cells. If the dominant female dies, the male's gonads stop working as testes and his egg-producing cells become active. At the same time, the largest of the non-breeding individuals living in the anemone becomes the functioning male. Quick sex change, anybody? No sharp objects, no hospital and no counselling. All these things make Nemo a cute but complex critter, and we have Hollywood to thank for showing the world the wonders of his daily existence. Ken was back in the water snapping away happily, this time at a little goby on the sand. Gobies, I thought, there's an interesting group of fish. I wondered if they had what it took to become Hollywood superstars, like their red-and-white-striped cousins across the reef. I watched a shrimp goby calmly surveying outside its burrow while its shrimp sentinel stood on duty - yup, with a little PR, I'm sure I could get a goby into the next awards ceremony.

This anemonefish is Amphiprion ocellaris also known as the false clownfish. Are you getting to see the differences? This is a pink anemonefish (Amphiprion perideraion) in a purple Magnifica anemone. The spinecheek anemonefish, Premnas biaculeatus A pair of spinecheeks with eggs A pair of false clownfish.