Dascyllus aruanus (Linnaeus, 1758)

Size

Whitetail dascyllus (Dascyllus aruanus) reaches a maximum total length of 10 centimetres (3.9 in), with a common adult size of 6 centimetres (2.4 in).

Appearance

Its body is white with three black vertical bars, and has a small mouth, a flat spine, and a large white spot between the eyes.

Similar Species

It closely resembles the closely related species D. abudafur, and may also be mistaken for D. melanurus, which has four black stripes instead of three.

Coloration Function

Body coloration does not change across its lifespan, and the bold black-and-white contrast is hypothesized to serve two purposes: attracting conspecifics, and signaling that the fish’s host coral is toxic to potential predators.

Growth and Lifespan

This species grows to about 6 centimetres in its first year of life, reaches full adult size by the end of its second year, and lives for another three to four years at its maximum 10-centimetre length before dying.

Habitat Association

Whitetail dascyllus is associated with coral reefs, and most often occurs in groups above the heads of Acropora corals.

Coral Symbiosis

This species, also called the black and white damselfish or humbug damselfish, maintains a symbiotic relationship with its host coral reef: the fish receives shelter from the reef, and exchanges nutrients in return.

Diet and Coral Benefit

As a planktivore, it acts as a "gardener" by grazing on unwanted algae, and excretes waste in the form of phosphate and ammonium that benefits the coral.

Feeding Range

To stay within the safety of the reef, the humbug feeds on nearby waste and small prey.

Native Distribution

Dascyllus aruanus is native to the Indo-Pacific, where it occurs east and north of the Sunda Shelf.

Group Size and Depth Range

It lives in small groups of around 30 individuals, and prefers small territories in shallow coral reefs between 1 and 10 meters deep.

Site Fidelity

Individuals rarely stray far from their birth home.

Inhabited Coral Traits

The coral reefs they inhabit are most often small, with lower species diversity.

Territoriality

Humbug damselfish are highly territorial, and will act to protect their coral shelters.

Interspecies Cohabitation

They can cohabit efficiently with Dascyllus marginatus in the same coral, having adapted similar behaviors and do not treat one another as competitors.

Spawning Season

Unlike many other fish species, black and white damselfish do not have a defined spawning season, and mating occurs daily.

Female Reproductive Output

Females may mate with multiple males, and can produce a new batch of up to 2000 eggs every two days.

Male Courtship Frequency

Males court females constantly.

Mating Selection Drivers

Non-random mating is selected by females, so only male preference affects spawning consistency, and multiple factors shape female selection of a male.

Female Preference Behaviors

Courting behavior and mate copying are the two dominant behaviors linked to female preference.

Mate Copying Definition

Mate copying occurs when a female chooses to mate with a male that has already mated with another female recently.

Courtship Rate and Reproductive Success

Males with higher courtship rates have higher reproductive success.

Courtship Display

To attract mates, males perform a "signal jump": they quickly rise up the water column before swimming back down.

Mating Success Bias

Recently mated males are also more likely to mate again with a new female.

Nest Site Preference

Females prefer to spawn at nesting sites that already hold eggs, as this indicates the male is higher quality and has successfully spawned with another female.

Mate Copying Benefits

This mate copying strategy reduces the energy females spend on choosing a mate, lowers the chance of selecting a low-quality male, and increases a female’s reproductive rate and success.

Male Nest Territoriality

Males are highly territorial of their nesting sites, and act aggressively toward other males during courtship.

Post-Spawning Male Behavior

After spawning is complete, males build and guard the nests.

Reproductive System Benefit

This consistent, efficient reproductive system is thought to be a major contributor to the stable conservation status of Dascyllus aruanus.