Throughout the entire marine aquarium trade, there probably is no more recognized animal than a clownfish, especially one that is within a host anemone. Even most individuals unfamiliar with the marine aquarium hobby or marine fish instantly recognize clownfish upon first sighting. Oftentimes aquarists are first drawn into this hobby because of the very first time they witnessed a clownfish swimming effortlessly through the deadly tentacles of their hosts. But is this a good choice as a first aquarium fish? Let's dive into the October issue of 'Fish Tales' and find out.

Meet the Family

Clownfish, although often assumed to be a family of their own, are actually damselfishes of the Family Pomacentridae. Within this damselfish family, the subfamily Amphiprioninae contains the 28 species of anemonefishes, also known as the clownfishes. This subfamily is comprised of two genera, four subgenera, and six complexes. Oddly enough, all but one of the anemonefishes are found within the genus Amphiprion. The odd fish out, the Maroon Clownfish, has a genus all to itself (see below). This monotypic genus was created because the Maroon Clownfish, unlike other clownfish, has a bony cheek spine below each eye located just prior to their gill covers.

"Complexes" are used to further segregate clownfish into species that share similar traits. Six complexes are recognized (see below). The Percula complex is comprised of only two species. These species are similar in that each has three white bands oriented vertically on a variable background, usually in shades of orange to black. Adults of the Tomato complex all have a single white bar behind their eye. Further research will be required, but it is possible that all five specimens of the Tomato complex may be a color variation of a single species. It has been noted that hybridizing has occurred in all species. In addition, captive breeding of the species A. frenatus resulted in color forms of A. frenatus, A. melanopus, and A. rubrocinctus (Marliave, 1985). Members of the Skunk complex are noted as rarely moving outside of their host anemone. Fishes from the Clarkii complex, the largest of the six complexes, also have three white bars on their body similar to the Percula complex. However, they are noted to wander up to several meters away from their host anemone on occasion. They also possess a forked tail which enables it to swim faster than other Anemonefishes. Perhaps this is why they are likely to wander more than their cousins. The Saddleback complex only has three species, and all are noted to have brown to black coloration, with some specimens having a small amount of orange. All three also have white bars or stripes, in some instances appearing as a saddle across their back. As noted above, The Maroon complex has a bony cheek spine below each eye just prior to their gill covers.

The Six Complexes of Anemonefish

Percula:	Tomato:	Skunk:	Clarkii:	Saddleback:	Maroon:
A. ocellaris	A. melanopus	A. akallopisos	A. akindynos	A. latezonatus	P. biaculeatus
A. percula	A. ephippium	A. leucokranos	A. allardi	A. polymnus
	A. frenatus	A. nigripes	A. bicinctus	A. sebae
	A. mccullochi	A. perideraion	A. chagosensis
	A. rubrocinctus	A. sandaracinos	A. chrysogaster
		A. thiellei	A. chrysopterus
			A. clarkii
			A. fuscocaudatus
			A. latifasciatus
			A. tricinctus

In the Wild

All Clownfish are found within the warm waters of the Indo-Pacific region except for A. latezonatus which is located in cooler, temperate seas around New South Wales, Queensland, and Lord Howe Island. Distribution is limited in most species, likely due to the short larval stage, but nevertheless some species are found on just about any reef in the Indo-Pacific region. Amphiprion clarkii has the largest distribution of the subfamily, extending beyond the tropical waters of the Indo-Pacific into the temperate seas off the Japan coast. Likewise, it is found in the cooler waters off the coast of Western Australia, and throughout the tropical waters from Melanesia to the Persian Gulf. In addition to A. clarkii, the subfamily extends to reefs found along the eastern coast of Africa to Tuamotu Archipelago, from the Red Sea to Lord Howe Island. Due primarily to their coexistence with sea anemones hosting zooxanthellae which, in turn, require sunlight, clownfish are generally located only in shallow waters.

Most readers are probably well aware of the obligate symbiotic nature of anemonefish with hosting anemones. This symbiotic relationship between the host anemone and anemonefish is termed "mutualism" as both members of the relationship benefit from the other partner. The single most important benefit of anemones towards anemonefish is protection. In the wild, clownfish are always located within a host anemone. A wild clownfish not hosting within a sea anemone is most often quickly consumed by any number of predators. It is the nematocysts of the sea anemone that ward off the attacks of groupers or other predators of anemonefish. Sea anemones gain several benefits from the hosting fish. In some areas, sea anemones will not survive without their host anemonefish. Butterfly fish are quick to dine upon anemones without a symbiotic partner standing guard. In some cases it has been noted that anemones will be consumed in less than 24 hours after removal of anemonefish (Fautin, 1986). In addition to protection, clownfish will achieve several tasks just from normal swimming. They will aerate the water around the tentacles, they will remove waste from the oral disc, and finally they will provide nitrogenous waste (food) to the host anemone. It is considered folklore, by many researchers, that an anemonefish will capture food items from the water column and "feed" the anemone. This has been known to happen within the confines of aquariums, but has not been witnessed by researchers in the wild.

Some readers, at this point, may be curious why the nematocysts of the sea anemone can offer protection to the anemonefish, and yet not harm the anemonefish. Quite frankly, we still do not know, although several hypothesis have been offered. Schlichter's hypothesis of camouflage was the first one offered, and was generally accepted until 1980. Schlichter's decade long study concluded that anemonefish will become coated with the mucus of the anemone by careful acclimation into the host. The result was an anemonefish that was "invisible" to the nematocysts. Opponents to this hypothesis argue that the shred mucus was a result of acclimation, not the explanation of how the mutualism can take place. Then in 1980 Lubbock released his hypothesis of inert mucus, which showed A. clarkii to have predominantly neutral polysaccharides. These neutral polysaccharides differ from that of the acidic mucus found on non-symbiotic fishes. Additionally, they failed to induce a triggered response from nematocysts, unlike the acidic mucus of the aforementioned non-symbiotic fish. All was well with this theory and Lubbock was a hero until he couldn't leave well enough alone. He took his study one step further and discovered that A. clarkii needed a four day acclimation upon leaving Stichodactyla haddoni for Entacmaea quadricolor. Obviously, this four day waiting period would not have been needed if the mucus of the fish was truly inert. Hence was born the hypothesis of thick mucus, which was rather short lived. It was believed that a clownfish inhabiting a host would have a thicker mucus coating which would in turn afford greater protection from the deadly nematocysts. Lubbock, once again, discounted his own hypothesis when he showed that the mucus coating of A. clarkii not in a host anemone was the same as one that was acclimated to a host anemone. Research continued until Lubbock proposed his hypothesis of customized mucus chemistry, which was based on the principle that a clownfish will reduce the amalgamation of substances within its mucus which stimulate nematocyst discharge. In 1984 the hypothesis of thick mucus was revisited when Brooks and Mariscal tried to discount the hypothesis of camouflage. Instead of discounting the work, they assisted in the confusion. They showed a limited, albeit shortened, acclimation period was required even when anemonefish were previously acclimated to fake anemones created with rubber bands and silicone. This required acclimation did not eliminate the hypothesis of camouflage, revived discussion on the hypothesis of thick mucus, and neither discounted nor proved the hypothesis of customized mucus chemistry. Confused yet? More recently, Miyagawa (1989) proposed the hypothesis of innate protection. He demonstrated that planktonic post larvae are stung when forced into contact with a host anemone. However, juveniles 12 to 24 hours older are not stung by the nematocysts. This 12 to 24 hour period directly coincides with the period that juvenile anemonefish institute a union with its preferred host anemone. Finally, Elliot set his sights on this complex interrelation. In 1994 he attempted to solve the mystery surrounding the mucus of the fish and anemone. What he found was that A. clarkii does not produce or have similar mucus to that of its host anemone, but it will collect the anemone mucus within its own once contact has been made to the anemone and thereby carry both the mucus of itself and the host anemone (Elliot, 1994). His 1997 work detailed how A. clarkii was innately protected from host anemones, however, A. ocellaris and A. perideraion are not (Elliot, 1997a). Furthermore, he showed larvae of ten species of clownfish will all be captured and consumed by the host anemones, but shortly after metamorphose this did not occur to certain species (Elliot, 1997b). Despite all of the research performed on this topic, no clear-cut answer has yet been determined. It remains one of life's great mysteries.

Clownfish definitely have their preferences of hosting anemones, though this preference is strangely not adhered to in captivity nearly as strongly as in the wild. Of the nearly 1,000 species of anemones, only ten species from five genera are ever used as symbiotic hosts for clownfish.

The anemonefish and their known natural symbiotic host anemones are detailed below with the anemone at the top of the chart and all natural hosting anemonefish below. It should be noted that A. clarkii is known to naturally host with each known hosting anemone. It should also be noted that in rare circumstances it has been noted that anemonefish may host in large-polyped stony corals such Euphyllia spp. or Goniopora spp. (Michael, Coral Realm).

Stichodactyla mertensii

A. akallopisos	A. fuscocaudatus
A. akindynos	A. latifasciatus
A. allardi	A. leucokranos
A. chrysogaster	A. ocellaris
A. chrysopterus	A. sandaracinos
A. clarkii	A. tricinctus

At about this time I would expect the reader to wonder how and why clownfish choose the anemone that they do. Thankfully, you are not the only person that has ever contemplated this. Arvedlund, et. al. (1999) found that the eggs of the clownfish were imprinted with cues during the development process. The eggs are laid nearby the base of the host anemone of the parents, where the imprinting occurs. Olfactory cues are imprinted according to the mucus released from the oral disc and tentacles of the anemone. These olfactory cues assist the juvenile clownfish in locating the same species of anemone that its parents preferred. Arvedlund's work was an extension of the work performed by Elliot in 1995 where they concluded clownfish species were able to track the scents of hosting anemones from as far away as 8m down current (Elliot, 1995).

All clownfish females are the result of males undergoing a sex change, or protandric hermaphrodites as they are called. In most host anemones a small harem of clownfish are present. Generally, this harem contains a single female, a single male, and several juvenile fish. The female is the most dominant member of the harem, and her constant attention to the harem ensures that the male does not develop into a female. When the female becomes absent from the harem, the male will assume the role of the female. Once a female, the fish cannot revert back to male. Both the male and female inhibit the sex change tendency of the juveniles. This phenomenon is often referred to as "psychophysical castration." When the male undergoes sex change and becomes a female, the juveniles will battle to determine who the most dominant member is. The winner will then grow testicles and become a male. These sex changes will occur in less than one month. In some instances, immigrating fish may disrupt this natural hierarchy. Some species (A. clarkii) have been noted to roam over 500 feet in search of another host anemone. In these cases, males and females may get thrown out of their host anemone by a stronger individual that left their original host anemone. Generally, these migrating specimens were displaced from their previous anemone in similar fashion. Juveniles will also migrate to nearby host anemones in hopes of moving up in the pecking order. In rare situations, juveniles may skip over the step of becoming a male, instead maturing from a juvenile into a female. This may occur if a male and female are not present in the host anemone, or a roaming juvenile is more dominant than the present female and male.

In most species of clownfish sexual dimorphism is present with the female being the larger of the two sexes. This is most pronounced in Premnas biaculeatus where the male is usually 30% of the size of the female. Although noted in Amphiprion clarkii and A. frenatus, sexual dichromatism is considered rare.

In the Home Aquarium

The majority of clownfish can be kept in home aquariums rather successfully, with several accounts of clownfish surviving for over 20 years. As with any marine fish, certain parameters must be met to ensure a happy, healthy fish. Similar to all the other fish I have covered in this column, pristine water parameters are assumed to be in place prior to introduction of the inhabitants. If optimum conditions are not yet present, this is obviously the first area of concern. For the purpose of this column, "optimum" should mirror natural sea water as closely as possible.

Once water parameters are under control the hobbyist needs to choose a clownfish and determine if it will require an aquarium to itself. Some species, like Premnas biaculeatus, are extremely aggressive fish. Juveniles can coexist with other fish, but as they age, their temperament will change as well. Adults of this species generally prefer an aquarium to themselves. Do not be surprised if Premnas biaculeatus decides to kill its tankmates, preferring to create a species aquarium for herself (and her mate). Despite Premnas biaculeatus gaining the reputation as the "meanest" clownfish, all clownfish are aggressive to some degree or another. Remember, they are damselfish after all. All clownfish will aggressively defend their host and a territory surrounding the host. Assuming you choose a clownfish other than P. biaculeatus, there are some fish that need to be avoided in their aquarium. Basically, any large predators, such as groupers or lionfish, need to be avoided. For these fish a clownfish represents an easy meal. Triggerfish or moray eels should also be added to this list. For a complete list, see below. Please note the list is specifically for Amphiprion species, as Premnas biaculeatus usually requires a tank to itself. However, this does not mean P. biaculeatus can be housed with predatory fish. They will likely either become food for the predators, or kill them in self-defense. Lastly, it is very important to note that for all species of clownfish the corallimorpharian commonly referred to as the elephant ear anemone, Amplexidiscus fenestrafer, will consume the clownfish. Do not place this anemone into any aquarium containing clownfish.

Compatibility chart for Amphiprioninae:

Fish	Will Co-Exist	May Co-Exist	Will Not Co-Exist	Notes
Angels, Dwarf	X			Should be excellent tankmates.
Angels, Large		X		Large Angels may become territorial.
Anthias	X			Should be excellent tankmates.
Assessors	X			Should be excellent tankmates.
Basses			X	Adults may consume clownfish.
Batfish	X			Should be excellent tankmates.
Blennies	X			Should be excellent tankmates.
Boxfishes	X			Should be excellent tankmates.
Butterflies	X			Should be excellent tankmates.
Cardinals	X			Should be excellent tankmates.
Catfish			X	Adults may consume clownfish.
Comet	X			Should be excellent tankmates.
Cowfish	X			Should be excellent tankmates.
Damsels		X		Best avoided except for large aquariums.
Dottybacks		X		Some dottybacks are very aggressive and are best housed by themselves.
Dragonets	X			Should be excellent tankmates.
Drums		X		Drums can become aggressive. Clownfish in first.
Eels		X		Some eels become large enough to consume clownfish.
Filefish	X			Should be excellent tankmates.
Frogfish			X	Adults may consume clownfish.
Goatfish	X			Should be excellent tankmates.
Gobies	X			Should be excellent tankmates.
Grammas	X			Should be excellent tankmates.
Groupers			X	Adults may consume clownfish.
Hamlets	X			Should be excellent tankmates.
Hawkfish		X		Large hawkfish may consume clownfish.
Jawfish	X			Should be excellent tankmates.
Lionfish			X	Adults may consume clownfish.
Parrotfish	X			Should be excellent tankmates.
Pineapple Fish	X			Should be excellent tankmates.
Pipefish			X	Pipefish are best housed by themselves.
Puffers		X		Some puffers can become aggressive. Clownfish in first..
Rabbitfish	X			Should be excellent tankmates.
Sand Perches		X		Sand perches can become incredibly aggressive. Clownfish in first.
Scorpionfish			X	Adults may consume clownfish.
Seahorses			X	Seahorses are best housed by themselves.
Snappers			X	Adults may consume clownfish.
Soapfishes			X	Adults may consume clownfish.
Soldierfish			X	Adults may consume clownfish.
Spinecheeks	X			Should be excellent tankmates.
Squirrelfish			X	Adults may consume clownfish.
Surgeonfish	X			Should be excellent tankmates.
Sweetlips			X	Adults may consume clownfish.
Tilefish	X			Should be excellent tankmates.
Toadfish			X	Adults may consume clownfish.
Triggerfish		X		Some triggerfish are incredibly aggressive. Clownfish in first.
Waspfish