The orange clownfish (Amphiprion percula) also known as percula clownfish and clown anemonefish, is widely known as a popular aquarium fish. Like other clownfishes (also known as anemonefishes), it often lives in association with sea anemones. A. percula is associated specifically with Heteractis magnifica and Stichodactyla gigantea, and as larvae use chemical cues released from the anemones to identify and locate the appropriate host species to use them for shelter and protection. This causes preferential selection when finding their anemone host species.
Although popular, maintaining this species in captivity is rather complex. The Great Barrier Reef Marine Park Authority regulates the number of collection permits issued to aquarium fish dealers who seek this, and other tropical fish within the Great Barrier Reef Marine Park.
The symbiosis between anemonefish and anemones depends on the presence of the fish drawing other fish to the anemone, where they are stung by its venomous tentacles. The anemone helps the fish by giving it protection from predators, which include brittle stars, wrasses, and other damselfish, and the fish helps the anemone by feeding it, increasing oxygenation, and removing waste material from the host.
Various hypotheses exist about the fish's ability to live within the anemone without being harmed. One study carried out at Marineland of the Pacific by Dr. Demorest Davenport and Dr. Kenneth Noris in 1958 revealed that the mucus secreted by the anemone fish prevented the anemone from discharging its lethal stinging nematocysts. A second hypothesis is that A. percula has acquired immunity towards the sea anemone's toxins, and a combination of the two has been shown to be the case. The fish feed on algae, zooplankton, worms, and small crustaceans.
Description
Amphiprion percula can grow to be in length, but is on average , and can be recognized by three white lines across their bright orange bodies, with no distinction in color between sexes. The anterior white bar is placed just behind the eye, the middle bar goes straight down the middle of the fish, and the posterior bar occurs near the caudal fin. An anterior projecting bulge also exists on the middle bar. In addition to the white coloring, black edging outlines each fin with varying thickness.
Reproduction
Since these fish live in a warm-water environment, they can reproduce all year long. Each group of fish consists of a breeding pair and none to four nonbreeders. Within each group there is a size-based hierarchy: the female is largest, the breeding male is second largest, and the male non-breeders get progressively smaller as the hierarchy descends. They exhibit protandry, meaning each fish is born male, but changes to female if the sole breeding female dies. If the female dies, the breeding male becomes the breeding female, and the largest nonbreeder becomes the breeding male.
The spawning process is correlated with the lunar cycle. At night time the moon maintains a higher level of alertness in A. percula and this increases the interaction with the males and females. Before spawning, the male attracts the female via courting behaviour. These courting actions include extending their fins, biting the female and chasing her. The males also swim rapidly in an upward and downward motion to attract the females. The nest site is also important for the survival of the eggs. The expected tenure of breeding females is roughly 12 years and is relatively long for a fish of its size, but is characteristic of other reef fish.
Why the nonbreeders continue to associate with these groups has been unclear. Unlike nonreproductives in some animal groups, they cannot obtain occasional breeding opportunities, because their gonads are not functional. They cannot be regarded as helpers at the nest, since their presence does not increase the reproductive success of the breeders. Recent research suggests that they are simply queuing for the territory occupied by the breeders, i.e. the anemone; nonbreeders living in association with breeders have a better chance of eventually securing a territory than a nonresident. A. percula is a very competitive fish and this causes the smaller fish to have stunted growth. A potential exists for a fish to ascend in rank by contesting its dominant. This depends on the relative body sizes of the two fish, and is very unlikely to happen since A. percula maintains well-defined size differences between individuals adjacent in rank. The higher the level of recruitment, the better chance a larva has of surviving long enough to become an adult fish. Large food supplies, low predator threats, and the availability of nearby anemones are all factors that affect their recruitment levels.
A. percula, like most coral reef fish, has a bipartite lifecycle, which has a scattering pelagic larval stage, whereas its resident phase is motionless. At the end of the pelagic phase, the larvae begin to settle on the coral reef and begin their recruiting process in the resident population. This could allow them to be preyed upon more easily, and lead to higher population mortality rates. Impairment of larval olfaction may also make them less able to locate appropriate reef habitats at the higher levels of ocean acidification that are projected to occur with increased carbon dioxide emissions. A paper published in Nature in 2020 cast doubt on the effect of acidification, stating "our findings indicate that the reported effects of ocean acidification on the behaviour of coral reef fishes are not reproducible, suggesting that behavioural perturbations will not be a major consequence for coral reef fishes in high CO2 oceans". A meta-analysis published in 2022 also found that effect sizes of studies assessing ocean acidification effects on fish behaviour have declined dramatically over a decade of research on this topic, with effects appearing negligible since 2015, representing one of the most extreme examples of the decline effect in ecology.
Development
The development of A. percula is relatively fast. After the eggs are fertilized, they are ready to hatch after about 6–7 days. After hatching, the larvae are very small and are transparent except for the eyes, yolk sac, and a few colors across the body. The larvae then sink to the benthic environment, but then swim to the upper water column. The larvae spend about a week floating among plankton and are transported by ocean currents.