Clownfish
Clownfish or anemonefishes are saltwater fish found in the warm and tropical waters of the Indo-Pacific. They mainly inhabit coral reefs and have a distinctive colouration typically consisting of white vertical bars on a red, orange, yellow, brown or black background. Clownfish developed a symbiotic and mutually beneficial relationship with sea anemones, on which they rely for shelter and protection from predators. In turn, clownfish protect the anemone from anemone-eating fish, as well as clean and fan them, and attract beneficial microorganisms with their waste.
Clownfish are omnivorous and mostly feed on plankton. They live in groups consisting of a breeding female and male, along with some non-breeding individuals. Clownfish have a size-based dominance hierarchy with the breeding female ranking at the top, followed by the breeding male and then the largest non-breeder and so on. When the female disappears, the breeding male changes sex and takes her place while the others move up the hierarchy. During reproduction, the female deposits eggs on a rock near their anemone, and the male fertilises them. After hatching, clownfish disperse into the open ocean as larvae, eventually settling on the bottom and searching for an anemone host as juveniles.
The recognisable colour patterns and social nature of clownfish have contributed to their popularity. They are featured in the Disney/Pixar film Finding Nemo and are sought after in the aquarium trade. The ocellaris clownfish ranks among the most commonly traded marine fish. Many captive clownfish were taken from the wild and this has led to their decline. Clownfish are more numerous in marine protected areas, where collecting is forbidden. Other threats to populations include global warming, which causes ocean warming and acidification.
Taxonomy
Clownfish are damselfishes in the genus Amphiprion, which was coined by Marcus Elieser Bloch and Johann Gottlob Theaenus Schneider in 1801 using the red saddleback anemonefish as the type species. Georges Cuvier considered the maroon clownfish morphologically different enough to be placed in its own genus Premnas in 1816. The status of Premnas has been disputed over the years, switching between a synonym or subgenus of Amphiprion and being its own genus. In 2021, two expansive phylogenetic analyses of damselfishes found the species to be within Amphiprion, making Premnas a junior synonym. In 1975, ichthyologist Gerald R. Allen placed clownfish in their own subfamily Amphiprioninae. A 2009 genetic study suggested creating the tribe Amphiprionini for clownfish and moving them to the subfamily Pomacentrinae. Eschmeyer's Catalog of Fishes considers the genus to be part of Pomacentrinae though scientific papers still use Amphiprioninae.Phylogeny
The clownfish lineage diverged from that of other living damselfishes around 35 million years ago during the late Eocene, and the most recent common ancestor of extant species is dated around 10.5 mya during the Early Miocene. A 2014 study placed their origin in the waters of the Malay Archipelago. Clownfish experienced an increase in species diversification starting around 5 mya, with two major adaptive radiations; one centred on the Malay Archipelago and a later one in the waters of the western Indian Ocean. There is genetic evidence for high amounts of interbreeding between species through their evolutionary history. Clownfish speciation has been linked to their sea anemone hosts, species of which can be found in different habitats and thus drove ecological separation.Prior to 2025, 28 living species of clownfish were recognised along with and two hybrids, the white-bonnet clownfish and Thielle's clownfish. In 2025, a new species, the Polynesian anemonefish, was classified. This fish was previously seen as a colour morph of the orange-fin anemonefish. In 1972, Allen listed five major clades or complexes based on morphology; percula, akallopisos, ephippium, polymnus and clarkii with the maroon clownfish being in a clade on its own. A 2014 study lists two more major clades: Australian and Indian, with the maroon clownfish under the percula clade and the orange-fin anemonefish and wide-band anemonefish being single-species clades. A 2021 study placed the members of the clade polymnus in the Indian clade, while a 2025 study found the maroon clownfish to be a single-species clade.
The following cladogram of 28 clownfish species is based on a 2025 genetic study, with clade/complex group labels based on a 2014 study.
Characteristics
Clownfish vary in size; the maroon clownfish can reach long while the orange clownfish reaches only. Females are larger than males and the smallest individuals in a group are only. Clownfish vary from oval-shaped to streamlined, and have rounded heads that lack scales between the snout and eyes. Teeth are present on both the oral and pharyngeal jaws but absent on the palate, and may be conical or chisel-shaped. Clownfish have saw-shaped edges along the operculum and under the eyes, which is the source of their genus name. The dorsal fin has 10 spines followed by 14–20 soft rays. It varies in shape; the ocellaris clownfish has a large recess between the spines and soft rays, while in the red saddleback anemonefish they are mostly continuous. Rays number 15–21 in the pectoral fins, five in the pelvic fins, 11–15 in the anal fin, and 14–15 in the caudal fin.Clownfish eyes are located at the sides of the head, as in most fish, but they can be seen from the front suggesting they have some binocular vision. Additional light can enter their eyes via small gaps between the iris and lens, and the fish can see both in colour and ultraviolet light. They have a single nostril opening with an arrow-shaped olfactory organ positioned around the midline of the olfactory cavity. This organ often contains extra flaps that are fork-like, a unique trait among fish. Their ears appear to be attuned for relatively low frequencies.
Colour patterns
Clownfish have distinctive colour patterns consisting of a red, orange, yellow, brown or black background with zero to three white vertical bars lined with black. Some species have a horizontal bar along the back, while the red saddleback anemonefish has no bars at all. Orange, yellow and red colouration is created by xanthophore pigment cells, black and brown by melanophores and the white bars by iridophores. Vertical bar formation starts at the front: species with only one bar have it at the head, those with two at the head and trunk, and those with three at the head, trunk and tail. Variations in the number of vertical bars between individuals of the same species occurs in the cinnamon clownfish, saddleback clownfish and Clark's anemonefish. Numerous colour morph mutations occur particularly in captive clownfish, including melanism, a "misbar" morph, and a "golden" morph that is caused by a lack of both melanophores and iridophores. There are also morphs with thickened and merged bars.A 2018 study found that clownfish species with only one or no vertical bars tend to be more specialised for anemone species with greater toxicity and shorter tentacles. Conversely, those with two or three bars are more likely to use more anemone species within their range, several of which have longer tentacles. The researchers suggest that vertical bars function in camouflage while warning colouration is more important for species that cannot hide in the tentacles of their hosts. This would be a unique case since it warns about another animal, namely the anemone. The study found no evidence for the use of the bars in species recognition, noting the geographic and ecological overlap between the similar-looking orange and ocellaris clownfish. By contrast, another 2018 study supported species recognition, finding little overlap between species with the same bar numbers within various clownfish communities. A 2024 study also found evidence for this function as the ocellaris clownfish can distinguish between individuals of different bar numbers.
Distribution and habitat
Clownfish inhabit warm and tropical waters spanning the Indian Ocean and the western Pacific; from the Red Sea to French Polynesia, and from Japan down to Australia. Some species are more widespread than others, and some live only around islands or archipelagos. Areas closer to the edges of their distribution have fewer species; both the Red Sea and French Polynesia have only one species each. By contrast, as many as 12 species can be found in an area in other regions such as Southeast Asian and northern Australian waters.Clownfish are limited by the distribution of their sea anemone hosts, which is usually near the surface at the sunlight zone where there are more photosynthetic microorganisms for anemones to depend on. This includes coral reefs and surrounding areas. Within a reef, clownfish species that use the same anemone species as their main hosts avoid competition by having individuals at different zones. Some species cohabitate on the same anemone host.
Behaviour and ecology
Feeding
Clownfish are omnivorous, and mostly feed on planktonic food such as algae, copepods and larval tunicates. Algae makes up much of the diet of the pink skunk clownfish. Clownfish also feed on the waste discharged by the anemone. Feeding takes up most of a clownfish's daily activity. Where predators are less common, clownfish may forage in an area as large as around their anemone. Otherwise they are restricted to feeding in the water column above their host. The dominant pair in a clownfish group feed further from the anemone than the smaller subordinates.Relationship with sea anemones
Clownfish have a mutualistic and symbiotic relationship with sea anemones. They acclimate themselves to their hosts by touching, nipping and fanning the tentacles over a period of minutes to days. The main benefit of living among anemones is protection from predators by anemone's stinging tentacles. A straying clownfish retreats to the safety of the tentacles when it encounters a potential threat, and it is always near its host, with smaller fish rarely leaving the oral disc. A clownfish may even swim into the coelenteron, though Allen observes this to be uncommon. Nighttime is spent resting deep among the tentacles. A less important benefit for clownfish is nourishment from the discharged waste and parasites.File:Clark's Anemonefish.jpg|thumb|right|Clark's anemonefish within a bubble-tip anemone. This clownfish utilises all ten anemone species that host clownfish species.|alt=Two clownfish on a sea anemone
Anemones are less dependent on clownfish than the fish are on them, as is evident as many individuals of host species lack clownfish. Nevertheless, clownfish contribute to the survival of their hosts by guarding from anemone-eating fish such as the raccoon butterflyfish. Other benefits they provide include the removal of copepod parasites, increased oxygen flow via the rapid movements of the fish's fins and the attraction of additional zooxanthellae by clownfish waste. A 2005 study found that anemones grew and regenerated faster in the presence of clownfish groups, and attributed this to ammonium from clownfish waste. Experimental evidence finds that when a clownfish is given small and large pieces of food, it consumes the former and give the latter to their anemone.
A total of ten sea anemone species are used by clownfish as hosts: the malu anemone, sebae anemone, magnificent sea anemone, corkscrew tentacle sea anemone, Mertens' carpet sea anemone, Haddon's sea anemone, giant carpet anemone, adhesive anemone, bubble-tip anemone, and beaded sea anemone. Some clownfishes are generalist in their choice of hosts, while others are more specialised. Clark's anemonefish is the most generalised species and utilises all ten anemone species, while nine clownfish species — the tomato clownfish, Chagos anemonefish, Pacific anemonefish, Seychelles anemonefish, Madagascar anemonefish, McCulloch's anemonefish, Maldive anemonefish, sebae clownfish, and maroon clownfish — use just one anemone species respectively. Desirable traits in a host include long tentacles to hide among. In addition, certain anemones like the beaded and bubble-tip sea anemone have tentacles with knob-like structures, which provide more surface area for the fish to conceal itself. The magnificent sea anemone can provide extra protection as clownfish can hide inside its soft body when it engulfs its tentacles. The potency of venom is also important; highly toxic anemone species tend to have smaller tentacles and so provide less shelter but more protection. Clownfish can cohabitate with other species on an anemone, including other clownfish, other fish such as the threespot dascyllus, and various decapods. Tolerance of the threespot dascyllus can vary between clownfish species.
The ability of clownfish to avoid being stung is attributed to their mucus coating. There is evidence that clownfish mucus mimics the molecules or bacteria of anemone mucus and lacks the trigger for the anemone's nematocysts. Mucus thickness may also play a role, but the evidence is ambiguous. There is dispute over how much of the mucus is innate to the clownfish and how much is gained from the anemone during the acclimation period. This may vary between species. A 2019 study found evidence that clownfish exchange microbiota with their anemone hosts.