Humbug Dascyllus

Whitetail dascyllus is up to 10 centimetres (3.9 in) in length but its common size is 6 centimetres (2.4 in) and is white with three black vertical bars.

It is morphologically identical to D. emamo, differing only in the sounds they make and their geographic distribution. It also appears very similar to the closely related D. abudafur. It may also be mistaken for D. melanurus, which has four black stripes instead of three. They have a small mouth, a flat spine, a black and white body with a large white spot between the eyes.

Associated with coral reefs, most usually in groups above Acropora coral heads. The black and white damselfish maintains a symbiotic relationship with its coral reef through exchange of nutrients for shelter. As planktivores, the humbug acts as a "gardener" by grazing on unwanted algae and excreting its waste in the form of phosphate and ammonium. In return, they can use the coral reef for protection and shelter, leaving only when necessary. To remain in the safety of the reef, the humbug will feed on waste and small prey nearby.

As a group that will stay at the same coral reef for their entire life, Dascyllus aruanus is very aggressive when it comes to their territory. All resources are heavily guarded and any unfamiliar species is seen as a threat. Living in a coral reef in shallow waters can make protection a full time job for some of these fish, making them extremely observant and wary. Some individuals are more aggressive than others, making an attack first response rather than observing for warning signs. As a species residing in shallow waters, there are multiple species of fish that come across the damselfish habitat. The humbug recognizes individuals of its own species by the dominant color pattern of the black stripes rather than movement.

Unlike other fish, black and white damselfish do not have a spawning season. Mating occurs daily, with females mating with multiple males in a season. A new batch of eggs can be produced every two days with up to two thousand eggs per batch and males court females constantly. Male preference is the only factor affecting the consistency of spawning, with non-random mating selected by females. However, many factors come into play when selecting a male. Courting and mate copying are the two dominant behaviors that correlate to female preference. Mate copying is when a female will mate with a male that just previously mated with another female. Males with higher courtship rates positively correlate with higher reproductive success.

As climate change continues to raise ocean temperatures, the humbug's lifestyle dwindles in response. Despite maintaining a status of Least Concern according to the IUCN Red List, the damselfish population remains susceptible to thermal stress and habitat loss by coral bleaching. According to a climate change study conducted in 2020, warmer oceans will result in an increase in mobility and a decrease in aggression by Dascyllus aruanus. The change in behavioral patterns are predicted to shift the social dynamics of a variety of fish that live in cohabitation with the humbug.