Distinguishing Features
Clownfish typically grow to between 5 and 13 cm and are coloured with a vivid orange hue and 3 vertical white stripes. Their fins are rounded more than pointed and have a fringe of black. They also feature a single nostril on either side of their snouts.
Their name most likely comes from their bright uniform and comical behaviour; ducking and darting around their host anemone or dashing out, full of bluster, to ward off an encroaching diver, thousands of times its body size, only to then turn and dart back to the safety of the anemone.
There are about 30 different species of anemonefish, of which the clownfish is just one, and it is likely that you'll see several different species in one single dive so it is important to be able distinguish between them.
A very similar species is the false clown fish, Amphiprion ocellaris, which have narrower black borders on the stripes and fins. They also have a taller anterior dorsal fin and 10 (not 11 dorsal spines). So unless you have a very keen eye and a picture of a 'real' clownfish handy it could be difficult to identify Amphiprion ocellaris.
Spinecheek anemonefish are another similar species and they can be recognised by their brown to red body, with 2 pale white bands 1 on either side of the face and a central white stripe running down the spine, making it obvious where the name came from.
Another common type is the Tomato anemonefish, Amphiprion frenatus, which tends to be dark red (especially juveniles) to black with 1 white side bar (juveniles may have 2 to 3 narrow bars). These can grow up to 14 cm in length and some varieties have darker coloration including more obscured stripes.
Finally you may want to know the difference between the clownfish and Clark's anemonefish (Amphiprion clarkii). This tends to have vivid black, white and yellow stripes, though the exact pattern shows considerable geographical variation. The tail fin is always lighter than rest of the body and usually you can see 2 white bands - 1 behind the eye and the other above the anus.Behaviour
Clownfish live in a symbiotic relationship with sea anemones normally the species Heteractis magnifica, Stichodactyla gigantean and Stichodactyla mertensii. The stinging cells (nematocysts) of the anemone are used to entrap fish as food. However the clown fish develops a mucous membrane on its body which offers protection from its otherwise lethal host.
One theory is that the membrane is based on sugars rather than protein and this prevents the nematocysts from firing, since the fish is not recognised as food. However it may owe more to the unique movements of the fish which indicate to the anemone that they are not to be treated as food. Evidence of this may come in the fact that juveniles, who have no mucous membrane can also seek refuge in an anemone without being stung.
Some believe that the anemone gains no benefit from the presence of the clown fish although some suggest that the fish contributes to the marriage by eating the parasites that would otherwise harm the anemone and by its movement; fanning fresh water around the anemone's body. Once a clownfish, or a number of them, have set up home in an anemone they will defend it vigorously, never straying further than a 30 cm or so from their host during their entire lifetime.Feeding Habits
The diet of the clownfish suggest that it is an opportunistic diner rather than a predator. It can wait until the anemone has stung and eaten its prey and then it gobbles up the leftovers, whether these pieces have not been eaten, or take the form of undigested excrement. It is also known to eat dead anemone tentacles, plankton, molluscs, crustacea and certain parasites that it finds on its host's body.Reproduction
The most extraordinary fact about clownfish is that they are hermaphrodites, i.e. they have sex-changing ability. Clown fish society has a hierarchical structure headed by a reproducing female and mating male, with a number of non-mating males waiting in the wings. Should the female die the mating male will turn into a female and choose to promote one of the non-mating males to active duty, a new dynamic to choosing the right partner!
Spawning year round, the eggs are laid in large batches around full moon, normally on a relatively flat surface near their host anemone. Both parents guard the eggs and fan them with fresh water for around 5 to 7 days. The eggs tend to hatch after darkness has descended upon the reef in an anti-predation strategy.Life Cycle
Upon hatching, the babies rise up to the sea's surface and begin the planktonic stage of their lives. When they descend back down the water column the fish must find a suitable anemone in which to live and seek protection.
When they are born, all clownfish are males. Juveniles who have just descended from the surface will be non-mating males within the host anemone unless a higher hierarchical place is available. Juveniles do not mature sexually until they are large enough to develop mature gonads and replace the dominant male.Predation
The host anemone offers great protection from most predators that know not to make contact with the anemone's potentially lethal tentacles. However, it seems that just about any larger fish such as eels and barracuda might eat a clownfish, given the chance.Distribution
Clownfish are tropical reef fish found in the warm waters of the Pacific Ocean (
Fiji),
the Red Sea, the Indian Ocean (
Thailand,
the Maldives and
Burma), and Australia's Great Barrier Reef but not in the Atlantic Ocean.
Many species ranges overlap with others and it is not unusual in places like
Malaysia and
Indonesia to see several different types of related anemone fish on one dive.
Ecological Considerations
A combination of factors have protected clown fish numbers against the threat of humans: they are found in small groups they are small fish without a great amount of meat on them, and are found living in quiet spots of the reef. However, due to their recent increased popularity, they have become very popular inhabitants of salt-water aquariums. Often this means they live without an anemone since these can be difficult animals to maintain in such conditions. Many reefs have been damaged in the drive to satisfy this market although many aquarium clownfish are now also tank bred.
Thankfully many local governments now restrict the numbers that can be removed, and the methods of their removal, simply to protect their numbers and preserve an important attraction to the scuba diving and snorkeling industry.
They continue to be in danger since coral reefs are under threat due to pollution, climate change, and damaging fishing practices such as trawl-fishing.
