The Orange Clownfish (Amphiprion percula) is an aquarium fish. Like other clownfish (also called anemonefish), it often lives in association with sea anemones. A. percula is associated specifically with Heteractis magnifica and Stichodactyla gigantea, and as larva 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 that are 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 it has been shown experimentally to be a combination of the two. The fish feeds on algae, zooplankton, worms, and small crustaceans.
The Amphiron percula can grow to be 11cm in length, but is on average 8cm, 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. This species can be mistaken for the similar species of clownfishes, A. ocellaris. This is known as the Ocellaris clownfish and sometimes referred to as the "false percula clownfish" or "common clownfish" due to its similar color and pattern. The "easiest" way to distinguish the two species is the fact that A. percula has 10 spines in the first dorsal fin and A. ocellaris has 11, which is a more reliable distinction than color patterns. The A. ocellaris does not have thick black edging outlining the fins.
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 0–4 non-breeders. 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 will only change to female if the sole breeding female dies. If the female dies, the breeding male changes sex, becomes the breeding female and the largest non-breeder 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 the 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. Depending on the size of the female spawn about 400–1500 eggs per cycle. The expected tenure of breeding females is approximately 12 years and is relatively long for a fish of its size, but is characteristic of other reef fish.
It has been unclear why the non-breeders continue to associate with these groups. Unlike non-reproductives in some animal groups, they cannot obtain occasional breeding opportunities, because their gonads are non-functional. They cannot be regarded as helpers at the nest, since it has been found their presence does not increase the reproductive success of the breeders. Recent research (Buston, 2004) suggests that they are simply queuing for the territory occupied by the breeders, i.e. the anemone; non-breeders living in association with breeders have a better chance of eventually securing a territory than a non-resident. The probability of a fish ascending in rank in this queue is equal to that of the individual outliving at least one of its dominants because an individual will ascend in rank if any one of its dominants dies, and not simply when its immediate dominant dies.
The development of the fish from juvenile to adult is dependent on the system of hierarchy, and can be described as density-dependent. There is aggression involved in these small families although usually not between the male and the females. The aggression usually exists between the males. The largest male will suppress the development of the next smallest male and the cycle continues until the smallest fish is evicted from the host anemone. Within each anemone, the regulation of the species is controlled by the female, since the amount of space for fish in her anemone is directly proportional to her size (which eventually reaches a maximum), so she ultimately controls the size of the other fish. Amphiprion percula are very competitive fish and this causes the smaller fish to have a stunted growth. There is the potential 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 maintain well-defined size differences between adjacent individuals in rank. However in an aquarium, this fish is peaceful, and it can live in an aquarium environment well.
