Clownfish or anemonefish are fishes from the subfamily Amphiprioninae in the family Pomacentridae. Thirty species are recognized, one in the genus Premnas, while the remaining are in the genus Amphiprion. In the wild they all form symbiotic mutualisms with sea anemones. Depending on species, clownfish are overall yellow, orange, or a reddish or blackish color, and many show white bars or patches. The largest can reach a length of 18 centimetres (7.1 in), while the smallest barely can reach 10 centimetres (3.9 in).
Ecology and habitat
Clownfish are native to warmer waters of the Indian and Pacific oceans, including the Great Barrier Reef and the Red Sea. While most species have restricted distributions, others are widespread. Clownfish live at the bottom of shallow seas in sheltered reefs or in shallow lagoons. There are no clownfish in the Atlantic.
Clownfish are omnivorous and can feed on undigested food from their host anemones, and the fecal matter from the clownfish provides nutrients to the sea anemone. Clownfish primarily feed on small zooplankton from the water column, such as copepods and tunicate larvae, with a small portion of their diet coming from algae, with the exception of Amphiprion perideraion, which primarily feeds on algae. They may also consume the tentacles of their host anemone.
Symbiosis and mutualism
Clownfish and sea anemones have a symbiotic, mutualistic relationship, each providing a number of benefits to the other. The individual species are generally highly host specific, and especially the genera Heteractis and Stichodactyla, and the species Entacmaea quadricolor are frequent clownfish partners. The sea anemone protects the clownfish from predators, as well as providing food through the scraps left from the anemone's meals and occasional dead anemone tentacles. In return, the clownfish defends the anemone from its predators, and parasites. The anemone also picks up nutrients from the clownfish's excrement, and functions as a safe nest site. The nitrogen excreted from Clownfish increases the amount of algae incorporated into the tissue of their hosts, which aids the anemone in tissue growth and regeneration. It has been theorized that the clownfish use their bright coloring to lure small fish to the anemone, and that the activity of the clownfish results in greater water circulation around the sea anemone. Studies on anemonefish have found that clownfish alter the flow of water around sea anemone tentacles by certain behaviours and movements such as “wedging” and “switching.” Aeration of the host anemone tentacles allows for benefits to the metabolism of both partners, mainly by increasing anemone body size and both clownfish and anemone respiration. 
Clownfish and certain damselfish are among the few species of fish that can avoid the potent poison of a sea anemone. There are several theories about how they can survive the sea anemone poison:
- The mucus coating of the fish may be based on sugars rather than proteins. This would mean that anemones fail to recognize the fish as a potential food source and do not fire their nematocysts, or sting organelles.
- The coevolution of certain species of clownfish with specific anemone host species and may have acquired an immunity to the nematocysts and toxins of their host anemone. Experimentation has shown that Amphiprion percula may develop resistance to the toxin from Heteractis magnifica, but it is not totally protected, since it was shown experimentally to die when its skin, devoid of mucus, was exposed to the nematocysts of its host.
In a group of clownfish, there is a strict dominance hierarchy. The largest and most aggressive female is found at the top. Only two clownfish, a male and a female, in a group reproduce through external fertilization. Clownfish are sequential hermaphrodites, meaning that they develop into males first, and when they mature, they become females. If the female clownfish is removed from the group, such as by death, one of the largest and most dominant males will become a female. The remaining males will move up a rank in the hierarchy.
Clownfish lay eggs on any flat surface close to their host anemones. In the wild, clownfish spawn around the time of the full moon. Depending on the species, clownfish can lay hundreds or thousands of eggs. The male parent guards the eggs until they hatch about six to ten days later, typically two hours after dusk.
Most clownfish are protandrous hermaphrodites, meaning they alternate between the male and female sexes at some point in their lives. Anemonefish colonies usually consist of the reproductive male and female and a few juveniles, who help tend the colony.  Although multiple males co-habit an environment with a single female, polygamy does not occur and only the adult pair exhibit reproductive behavior. However, if the largest female dies, the social hierarchy shifts with the breeding male exhibiting protandrous sex reversal to become the breeding female. The largest juvenile will then become the new breeding male after a period of rapid growth. The existence of protandry in clownfish may rest on the case that non-breeders modulate their phenotype in a way that causes breeders to tolerate them. This strategy prevents conflict by reducing competition between the males for one female. For example, by purposefully modifying their growth rate to remain small and submissive, the juveniles in a colony present no threat to the fitness of the adult male, thereby protecting themselves from being evicted by the dominant fish. 
The reproductive cycle of clownfish is often correlated with the lunar cycle. Rates of spawning for clownfish peak at approximately the first and third quarters of the moon. The timing of this spawn means that the eggs will hatch around the full moon or new moon periods. One explanation for this lunar clock is that spring tides produce the highest tides during full or new moons. Nocturnal hatching during high tide may reduce predation by allowing for a greater capacity for escape. Namely, the stronger currents and greater water volume during high tide protects the hatchlings by effectively sweeping them to safety. Before spawning, clownfish exhibit increased rates of anemone and substrate biting, which help prepare and clean the nest for the spawn. 
In terms of parental care, male clownfish are often the caretakers of eggs. Before making the clutch, the parents often clear an oval sized clutch varying in diameter for the spawn. Fecundity, or reproductive rate, of the females usually ranges from 600 to 1500 eggs depending on the size of the female. In contrast to most animal species, the female only occasionally takes responsibility for the eggs, with males expending most of the time and effort. Male clownfish care for their eggs by fanning and guarding them for 6 to 10 days until they hatch. Studies have shown that, in general, eggs develop more rapidly in a clutch when males fanned properly and that fanning represents a crucial mechanism of successfully developing eggs. This suggests that males have the ability to control the success of hatching an egg clutch by investing different amounts of time and energy towards the eggs. For example, a male could choose to fan less in times of scarcity or fan more in times of abundance. Furthermore, males display increased alertness when guarding more valuable broods, or eggs in which paternity was guaranteed. Females, on the other hand, display generally less preference for parental behavior than males. All these suggest that males have increased parental investment towards the eggs compared to females. 
Clownfish make up 43% of the global marine ornamental trade, and 25% of the global trade comes from fish bred in captivity, while the majority are captured from the wild, accounting for decreased densities in exploited areas. Public aquaria and captive breeding programs are essential to sustain their trade as marine ornamentals, and has recently become economically feasible. It is one of a handful of marine ornamentals whose complete life cycle has been closed in captivity. Members of some clownfish species, such as the maroon clownfish, become aggressive in captivity; others, like the false percula clownfish, can be kept successfully with other individuals of the same species.
When a sea anemone is not available in an aquarium, the clownfish may settle in some varieties of soft corals, or large polyp stony corals. Once an anemone or coral has been adopted, the clownfish will defend it. As there is less pressure to forage for food in an aquarium, it is common for clownfish to remain within 2-4 inches of their host for their entire lifetime. Clownfish, however, are not obligately tied to hosts, and can survive alone in captivity.
- Genus Amphiprion:
- Amphiprion akallopisos – Skunk clownfish
- Amphiprion akindynos – Barrier Reef Anemonefish
- Amphiprion allardi – Twobar anemonefish
- Amphiprion barberi
- Amphiprion bicinctus – Twoband anemonefish
- Amphiprion chagosensis – Chagos anemonefish
- Amphiprion chrysogaster – Mauritian anemonefish
- Amphiprion chrysopterus – Orange-fin anemonefish
- Amphiprion clarkii – Yellowtail clownfish
- Amphiprion ephippium – Saddle anemonefish
- Amphiprion frenatus – Tomato clownfish
- Amphiprion fuscocaudatus – Seychelles anemonefish
- Amphiprion latezonatus – Wide-band Anemonefish
- Amphiprion latifasciatus – Madagascar anemonefish
- Amphiprion leucokranos – Whitebonnet anemonefish
- Amphiprion mccullochi – Whitesnout anemonefish
- Amphiprion melanopus – Fire clownfish
- Amphiprion nigripes – Maldive anemonefish
- Amphiprion ocellaris – Clown anemonefish
- Amphiprion omanensis – Oman anemonefish
- Amphiprion pacificus – Pacific anemonefish
- Amphiprion percula – Orange clownfish
- Amphiprion perideraion – Pink skunk clownfish
- Amphiprion polymnus – Saddleback clownfish
- Amphiprion rubacinctus – Red Anemonefish
- Amphiprion sandaracinos – Yellow clownfish
- Amphiprion sebae – Sebae anemonefish
- Amphiprion thiellei – Thielle's anemonefish
- Amphiprion tricinctus – Three-band anemonefish
- Genus Premnas:
- Premnas biaculeatus – Maroon clownfish
In popular culture
Allard's clownfish (Amphiprion allardi).
Pink skunk clownfish (Amphiprion perideraion).
Yellow clownfish (Amphiprion sandaracinos) and sea anemone off Sulawesi, Indonesia.
Yellowtail clownfish (Amphiprion clarkii) with sea anemone.
Orange-fin anemonefish (Amphiprion chrysopterus) is one of the few anemonefish with a white tail.
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