Amphiprion ocellaris, also known as the Ocellaris clownfish, False Percula clownfish or Common clownfish, is a marine fish belonging to the family Pomacentridae which includes clownfishes and damselfishes.
The Common clownfish is a small fish which grows up to 11 cm (4.3 inches). Its body has a stocky appearance and oval shape. It is compressed laterally, with a round profile. The coloration of its body is orange to reddish-brown, but it can also be black in some particular areas such as the Northern Territory in Australia. It has three vertical white stripes outlined with a fine black line. The first passes just behind the eye, the second in the middle of the body widens forward to the head centrally and the third one circles the caudal peduncle. All the fins are also outlined with a fine black line. Amphiprion ocellaris is often confused with Amphiprion percula, which possesses exactly the same colours and patterns at first sight but distinguishes itself by the thickness of the black outlines.
The species Amphiprion ocellaris belongs to the class Osteichthyes which contains bony fish and ray-finned fish. A. ocellaris is the most basal species in the genus Amphiprion which is closely related to the genus Premnas. The species' most closely related ancestor is Amphiprion percula, the Orange clownfish. It is thought that A. ocellaris specialized after diverging from the Premnas genus, and scientific evidence confirms that all clownfish belonging to the genus Amphiprion could withstand the stings of only one type of anemone, after further diverging the 28 different species of clownfish including A. ocellaris specialized to be able to resist the poisonous stings of many different species.
Amphiprion ocellaris typically lives in small groups on outer reef slopes or in sheltered lagoons at a maximal depth of 15 metres (49 ft). It inhabits three different species of sea anemones: Heteractis magnifica, Stichodactyla gigantea and Stichodactyla mertensii.
Amphiprion ocellaris is a diurnal fish. It is a protandrous hermaphrodite, which means the male can change its gender to female during its life, and lives in a harem in which an established dominance hierarchy manages the group and keeps individuals at a specific social rank. It is aggressively territorial and is completely dependant on its sea anemone, which provides a safe shelter as well as a nest. The associative relationship that binds the clownfish and the sea anemone is called mutualism. On one hand, the fish can live within the sea anemone's tentacles and use it as a shelter because it has developed a thin layer of mucus which covers its body as protection against the stinging anemone's tentacles. On the other hand, the presence of the clownfish can be interpreted as a lure to attract potential anemone's preys close to the tentacles. And the clownfish can also defend the anemone against some reef fishes which could eat the tentacles.
Amphiprion ocellaris are reliant on sea anemone for shelter (they have a symbiotic relationship with the sea anemone). Sea anemone are protection for the fish and their nests. This is because when Amphiprion ocellaris are in the open waters, they have a higher risk of predation. It is postulated that the fanning behavior of the fish and removal of parasites promotes the health of sea anemones which contain Amphiprion ocellaris fish. In addition, the anemone provides protection for the fish with its tentacles, however, the fish’s mucus protection prevents it from being stung by the tentacles.
According to a study performed on Amphiprion ocellaris, queues is the term for social groups of Amphiprion ocellaris. This is because these fish form social hierarchies, or social rank, by “outliving” the more dominant members of the group. The dominant pair of each queue reproduces more compared to the subordinate fishes. This is the reason for why these individuals should adopt various tactics in which they increase their probability of attaining social dominance. There are two types of Amphiprion ocellaris, settlers and switchers. Settlers prefer shorter queues, while switchers will usually move after settlement. However, studies show that there is no difference in the characteristics between switchers and non-switchers, and there is no data demonstrating that Amphiprion ocellaris utilize the switching tactic for dominance. Although settlement preferences increase the likelihood of gaining social dominance, switching could have the function of increasing social dominance benefits after social dominance has been acquired.
Juvenile Amphiprion ocellaris
Juvenile Amphiprion ocellaris have difficulty finding an anemone to live in (since they need anemone for survival and shelter). The difficulty also arises in the fact that there exists a hierarchy in each anemone. Thus, when a new juvenile enters an anemone, it begins at the bottom of the social ladder where it is often the victim of aggression by other clownfish. This aggression from other Amphiprion ocellaris in the anemone can cause the juvenile to be chased out of the anemone.
Group size and patch size
Studies have shown that there is a correlation between the size of the group and and the size of the patch; however this correlation provides no implication that subordinate group members have less resources. More likely, it is the effects of the patch size on the group member that dominates interactions. An experiment was performed to study which one of these above mechanisms was responsible for the positive correlation between the group size and patch size. The scientists argued that the correlation between the group size and patch size is because of the the indirect consequence of the positive relationship between the dominant group member’s length and the anemone size. The length of the dominant group member limits the group size because the length of the dominant group member prevents the group of the subordinate group members. This data shows that the patch size and group size correlation does not necessarily imply the decrease in resources of group members subordinate to the dominant group member.
There is not much data on the reproduction of Amphiprion ocellaris. However, similar behaviors throughout all anemone fishes have been recorded. These fish have monogamous mating systems, and are territorial of their anemone. Males become more aggressive during spawning. Male behavior also changes to attract females: biting, chasing, fin extension. Before spawning, the male prepares the nest near the anemone (so that the tentacles of the anemone can protect the nest). After the male chases the female to the nest, the female begins the spawning process. She lays eggs for about one to two hours, and then leave the nest for the male to fertilize the eggs. The eggs take approximately six to eight days to hatch (this time period can be affected by the temperature of water). Because of the external fertilization, males usually care for the eggs. They also have responsibilities for eating fungi-infected or infertile eggs, and fanning the eggs.
All of the individuals first develop into males and then later there is a possibility that they become females (protandrous hermaphrodites). This also can be termed as plasticity in sex differentiation. This is shown when there are males, females, and juveniles together in an anemone. In the social groups, the female is the dominant and largest member, with signs of aggression towards other members of the social group. The next rank in the social hierarchy were the fishes that will become males and other fishes that stay as non-reproductive. One experiment placed three juvenile anemonefish in a tank and their behaviors were observed over a month. Observations about social rank were made throughout this period, based on interactions with the group. There was also a noticeable correlation between aggressive behaviors and appeasing behaviors. There were many other signs of dominance in this hierarchy, such as the continuous occupation of territory in the tank by the dominant fish, and increase in body mass of the dominant fish compared to that of lower ranked fish (indicating growth suppression). In addition, a difference in certain steroid levels of the fish indicated that there was reproductive suppression also occurring. The individuals that were ranked lower were reproductively suppressed, which was apparent around the first stage of when the group was formed. Gradually, the sex differentiation and dominance were formed after social interactions occurred for awhile.  Another experiment performed was if we removed the female from the anemone, then the next dominant male would become the female. There is also a dominance hierarchy that exists here. Females actually utilize aggressive dominance to control the males to prevent the formation of other females, and dominant males prevent juvenile males from mating.
Amphiprion ocellaris feed on plankton and algae, thus they are considered omnivores. Feeding is also affected by the hierarchy in Amphiprion ocellaris groups. Since the smaller, less dominant fish face aggression from the more aggressive fish, they have less energy to forage for food. Thus, they usually do not eat as much as the dominant fish do, because of reduced energy, but also because of the increased danger they face when they leave their anemone since they are smaller. In other words, the larger fish will usually travel farther than the smaller fish. Generally, the Amphiprion ocellaris feed on algae, copepods, and zooplankton. 
In nature, the false percula clownfish will host Heteractis magnifica and Stichodactyla gigantea. However, in captivity in a reef aquarium, the false percula will host other species of anemone, including Entacmaea quadricolor. In addition, clownfish may adopt a surrogate host as opposed to an anemone, such as Euphyllia divisa, xenia coral, etc.
|Wikimedia Commons has media related to Ocellaris clownfish.|
- Aquaticdatabase entry for Amphiprion ocellaris (Ocellaris Clownfish).
- Photo Gallery of Amphiprion ocellaris and their eggs (ger.)
- Aquarium Wiki care information on Amphiprion ocellaris
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