Since the release of Finding Nemo, coral reef clownfish have joined the ranks of whale sharks and manta rays and become one of the most beloved species for scuba divers.
These pint-sized anemonefish are colourful, fun to photograph, and packed with personality. They also display some fascinating and unique behaviours, forming mutually beneficial relationships with an unlikely ally - the sea anemone. Affectionately nicknamed Nemo fish, these lovable little reef dwellers come in a wide variety of colours and can be spotted at dive sites around the world.
There are 30 known species of clownfish and while you're probably familiar with the classic orange and white clown anemonefish - the species Nemo was inspired by - clownfish actually come in a wide variety of shapes and sizes. Depending on the species, anemonefish can be yellow, orange, red, or black, with or without their signature white bars or patches. The largest clownfish can reach a length of 17 centimetres, while the smallest top out at just seven to eight.
Anemonefish evolved over the course of millennia to survive the potent poison of their host species. But, scientists still aren't exactly sure how they do it! One theory is that the chemical signature of the mucous coating that covers the fish isn’t recognised as a threat by the anemone, which therefore doesn't fire its stinging cells. But, anemonefish could also have evolved an immunity to the toxins of their hosts - allowing themselves to be stung without feeling the effects.
Anemonefish have also developed the ability to balance their own populations through a surprising role reversal. All clownfish begin their lives as small males that live in a group ruled over by a dominant female. She only mates with the largest male in the group. If the female dies, this male changes sex to take over the role as a female and the other males move up a step in the queue. It is thought that this unusual life history has evolved because of the risks involved in moving away from the anemone are outweighed by the benefits of waiting in line for a chance to breed.
Clownfish lay clutches of eggs inside or next to their anemone hosts for added protection. The male then cares for its unborn young for six to ten days until they hatch and disperse - each starting its own search for the perfect host anemone.
Anemonefish can be found in warm waters around the world, including the Indian Ocean, Red Sea, and Pacific Ocean, from Southeast Asia, Oceania, and the Indo-Malaysian region all the way to the Maldives, coastal Africa, and the Middle East.
While most clownfish species are region-specific and found in just one small area, others are widespread. But, no matter where in the world you're hoping to find Nemo, you should start the search in their favourite habitat. These feisty underwater entertainers prefer to live on sheltered reefs and in shallow lagoons and won’t stray too far from their host anemones.
Ecology and Behaviour
While they are commonly referred to as clownfish, or just Nemo, anemonefish are aptly named for their fascinating relationships with the anemones they inhabit. One anemone can host a single fish or an entire colony. This living home protects the anemonefish from predators with its stinging tentacles, offering a safe place to rest, nest, and guard the next generation of Nemo fish. And, in return, the anemonefish defends its anemone from potential predators and parasites - that's why they do that little dance for divers. Believe it or not, that's actually a warning to keep away!
'Nemo' and the evolution of helping behaviour
Anemonefish are omnivores with a twist. Much of their diet comes from the undigested food and faecal matter of their host anemones. They may also feed on zooplankton, algae, and even the tentacles of the anemones they live in. The anemone also benefits, absorbing nitrogen and other nutrients from the skin and excrement of its partner. The swimming motion of the fish also circulates water around the anemone's tentacles, bringing new nutrients, oxygen and potential prey close enough to catch.
As a diver, you can help keep clownfish safe by maintaining perfect buoyancy, well away from the reef. And, as cute as all that swishing and darting might be - remember, the anemonefish dance is actually a sign of distress. So, once you notice Nemo starting to get nervous, it's time to move on. Photographers should try to keep their flashes to a minimum, with no more than four or five shots per subject. More than that can leave an anemonefish blinded, stunned, and vulnerable to passing predators.
You can also positively contribute to clownfish conservation by not purchasing wild-caught specimens from the reef. If you're an aquarium enthusiast, opt for an ethically sourced and captive-bred animal instead.
Lastly, scuba divers can opt for reef-safe sunscreen, insect repellant, and mask defogger rather than traditional products. These earth-friendly alternatives often use natural ingredients in place of harsh chemicals that have been linked to coral bleaching.