The Domino Damselfish imitates a “domino” in their juvenile coloration!

The Domino Damsel Dascyllus trimaculatus is one of the most striking damselfish as a juvenile. This small black fish has a distinct white spot on the forehead and a prominent white spot on the upper side. Thus it is also known as the Three Spot Damsel or Three Spot Dascyllus. Elegant in form and high in contrast, it quickly catches the eye.

In the mature fish, the white marks will most likely disappear or leave just a remnant spot on the side. The body colors of the full grown adult range from light to dark gray, depending on their nuptual state or activities they are involved in. Those that are in a breeding mood, or engaged in aggressive interactions, tend to be white or light gray. When they are feeding or being cleaned, their bodies tend to be black or gray. They can reach up to 5 1/2 inches (14 cm) in length, though 5 inches is more likely in the aquarium.

These damsels are very hardy making them suitable for beginner aquarists. They are easy to keep and gregarious as juveniles, swimming in large groups together. This changes as they get older, however, because they become extremely aggressive and territorial. In a captive environment this aggression becomes disastrous for inappropriate tank mates. Even aggressive fish added to the tank after this fish has become established and full grown, will be attacked. Thus, an aquarist may need to set up a separate tank for their Domino Damsel if it will not allow any other fish into their domain.

Tank mates need to be carefully chosen. It’s best to keep only one Domino Damsel per tank, with no other damselfish. Make sure that the tank has aggressive or large semi-aggressive fish. Male and female pairs need a large tank or may have serious squabbles which result in injury. Peaceful and smaller semi-aggressive fish will be attacked, especially in smaller tanks.

Provide a tank that is at least 55 gallons for one Domino Damsel with rock work creating places for them to hide. They are planktivores which eat continuously in the wild, so should be fed at least 3 times a day in the aquarium. Feeding them often has been known to help with aggression to a minor degree. Providing many places for them to hide as juveniles will help them adjust.

For more Information on keeping saltwater fish see:
Marine Aquarium Basics: Guide to a Healthy Saltwater Aquarium

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Perciformes
  • Family: Pomacentridae
  • Genus: Dascyllus
  • Species: trimaculatus
Domino Damsel – Quick Aquarium Care
  • Aquarist Experience Level: Beginner
  • Aquarium Hardiness: Very Hardy
  • Minimum Tank Size: 55 gal (208 L)
  • Size of fish – inches: 5.5 inches (14.00 cm)
  • Temperament: Aggressive
  • Temperature: 72.0 to 82.0° F (22.2 to 27.8&deg C)
  • Range ph: 8.1-8.4
  • Diet Type: Omnivore
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Habitat: Distribution / Background

The Domino Damsel Dascyllus trimaculatus was described by Ruppell in 1829. They are found in the Indo-Pacific from the Red Sea and East Africa to the Pitcairn Island and Line Islands. They are also found from southern Japan down to Sydney, Australia. They are not found in Hawaii or the Marquesas Islands. This species is not listed on the IUCN Red List of Threatened Species.

This species is best known by the name Domino Damsel. There are a number of other common names as well, and most relate to their coloring as juveniles. These include Domino Damselfish, Three Spot Damsel, Three Spot Damselfish, Three Spot Dascyllus, Threespot Humbug, Threespot Damselfish, White Spot Puller, and Damsel Fish.

This species is a member of the very large Pomacentridae family of Damselfish and Anemonefish. It belongs to the subfamily Chrominae in the Dascyllus genus. There are currently 10 recognized species in this genus and they are only found in the Indo-Pacific.

The Dascyllus species are very deep bodied damselfish. They have a commensal relationship with corals and are often found hovering around isolated coral heads in groups. These groups range in size depending on the size of the coral. Once a Dascyllus has located a home at a coral colony it remains there.

They hide within the coral colony when frightened and use it as protection at night. In turn, the coral colony benefits from the fish waste and water movement they produce between their branches. In fact, studies have shown those corals with groups of Dascyllus grow faster and larger than those without. These damsels have the ability to visually tell the difference between a nearby herbivore and a predator by the placement of their eyes and the shape of their mouths.

The largest dominant fish in a group is always male, but when the dominant male is removed the largest female then transforms into the dominant male. With some species there may be several females in the process of becoming male even while subordinate. Many Dascyllus species are known to be hermaphrodites, with all starting life as female. Yet it is also thought that there are some species that are gonochorists, where they are born as either male or female.

Similar to clownfish, this genus produces sounds to communicate. They make at least three distinct pulse sounds, and the larger the specimen the lower the frequency. Chirps and pops are audible with some species when the males are engaged in fighting, during courting, and when caring for and defending eggs in the nest site.

Of all the damselfish species only two (possibly three) from the Dascyllus genus are known to associate with anemones. These are the Domino Damsel Dascyllus trimaculatus, the Hawaiian Dascyllus Dascyllus albisella, and possibly the Strasburg’s Dascyllus Dascyllus strasburgi. Unlike their Clownfish relatives they are only found with anemones as juveniles, so are considered “facultative symbionts.” Clownfish, on the other hand, live with anemones their entire lives so are known as “obligate symbionts.”

Dascyllus are very attractive as juveniles, exhibiting dynamic color patterns. As juveniles they can be kept in a group, but as they age they become extremely territorial and mean in the confined space of the aquarium. They will be aggressive with their own kind and other damsels, as well as other fish that are not equally boisterous and pugnacious.

Domino Damselfish adults are found in lagoon patch reefs, reef faces, back reefs, fore reef slopes, and coastal and off-shore coral and rocky reefs. Adults are found in small to large groups of 3 to 25, and an odd adult can be found near a sea anemone, although they prefer stony branching corals. Juveniles are found in very large groups with large sea anemones, sea urchins, or over small coral heads.

They can be found at depths between 3 to 180 feet (1 to 55 m). Both adults and juveniles feed on copepods, benthic algae and weeds, and other planktonic crustaceans. Benthic algae ingested is from consuming copepods and other small crustaceans that inhabit algae covered surfaces.

  • Scientific Name: Dascyllus trimaculatus
  • Social Grouping: Varies – They are mostly found in groups up to 25 individuals, though occasionally alone.
  • IUCN Red List: NE – Not Evaluated or not listed


The Domino Damsel is a deep bodied fish that’s not built for speed as well as other damselfish, so they tend to stay closer to their host coral. Some interactions, such as being engaged in fighting or when courting or caring for their nest, may result in these fish producing distinct pulsing sounds. They can reach up to 5 1/2 inches (6 cm) in length, though typically only grow to about 5 inches in the aquarium. In the wild their life span is 2 to 8 years, though they may live up to 20 years in captivity.

Juveniles have black scales with the centers being blue. Their fins are all black, though the spaces between the rays on their dorsal fin have a bluish color. They have three small white spots on their body with one on the forehead and one on each side of their upper back just below the middle of their dorsal fin, thus earning them the name “Domino” Damsel.

Adult coloration varies from light gray to dark gray and the dot on their forehead disappears, though the white spots on their sides may remain. Some individuals that occur where the waters are relatively turbid will have partly red-orange on the fins and adjacent parts of the body. When feeding adults tend to be black or gray overall. Aggressive interactions, spawning or courtship will tend to turn their body color to white or light gray, while the eye stays black. At times a black bar can be seen through the eyes.

There are some Dascyllus that are similar in appearance to the Domino Damsel:

  • Hawaiian Dascyllus Dascyllus albisella
    The Hawaiian Dascyllus is also black but has a large white oval on each side of the body and a white dash across their forehead. The Hawaiian Dascyllus is found only around the Hawaiian and Johnston Islands. Juveniles associate with the the Delicate Sea Anemone Heteractis malu.
  • Yellow Threespot Dascyllus Dascyllus auripinnis
    The Yellow Threespot Dascyllus behaves the same as the Domino Damsel and looks very similar too, especially in body shape. Their overall color is bluish gray in the adults, however is different in the belly area, which is yellow. Also, the bottom fins are yellow with black edging and there is a dot of yellow between each of their blue dorsal rays. This beauty is a highly sought after Dascyllus!
  • Strasburg’s Dascyllus Dascyllus strasburgi
    Juveniles are identical to the Domino Damsel but as adults they have a grayish colored body and the fins are white. This damselfish is found only in the south central Pacific Islands, called the Marquesas, and are rarely available in the hobby except as a specialty order. As juveniles they are usually found associated with the Adhesive Sea Anemone Cryptodendrum adhaesivum and possibly the Delicate Sea Anemone Heteractis malu.

Male Domino Damselfish are larger and are the dominant fish in a group or pair. These damselfish are all born female and some females may have slightly undeveloped male organs to allow them to quickly turn into a male if the dominant male disappears.

  • Size of fish – inches: 5.5 inches (14.00 cm) – They can reach up to 5 1/2 inches, but typically grow to about 5 inches in captivity.
  • Lifespan: 20 years – In the wild their life span is 2 to 8 years, but in captivity this species may live up to 20 years.

Fish Keeping Difficulty

The Domino Damselfish is among the easiest of all marine fish to care for. Being very hardy it is suitable for the beginner saltwater hobbyist. The only things they really need are a few places to hide in rockwork and to be fed 3 times a day. Even though they are quite durable, they still can fall ill if exposed to poor water conditions for too long.

Even though they are gregarious as juveniles and can be kept in a group, they become very aggressive as they age. Adults will attack any other damselfish as well as other tankmates that are not equally aggressive. These fish need 55 gallons or more and should be kept singly, unless the tank is very large with many hiding places for shelter. Doing normal water changes, feeding them a variety of foods several times a day, and having the proper tank mates are necessary to keep this damselfish.

  • Aquarium Hardiness: Very Hardy
  • Aquarist Experience Level: Beginner – They are suitable for a beginner, but tankmates must be selected with great care.

Foods and Feeding

Domino Damselfish are omnivores. They are mostly planktivores in the wild that feed on copepods and other planktonic crustaceans, but also consume benthic algae and weeds as they ingest small crustaceans that are inhabiting algae covered surfaces. In the aquarium provide variety in their diet that includes meaty foods such as mysis shrimp, enriched brine shrimp, krill, finely chopped shrimp or other crustacean flesh, and other meaty foods. If there is no algae in the tank, then a little flake food for herbivores can be given.

They will feed in the water column and at the top of the tank. If feeding pellets, make sure they are wet before adding them to the tank so air will not get into the damsel’s digestive tract, which can cause issues. It is best to feed small amounts of food several times a day. These fish eat constantly in the wild so they do better when fed at least 3 times a day.

  • Diet Type: Omnivore – They lean more towards a planktivore, feeding on planktonic crustaceans in the water column, and incidentally ingesting algae.
  • Flake Food: Yes
  • Tablet / Pellet: Yes – Make sure the pellets are wet before adding to prevent air from getting trapped in their digestive tract.
  • Live foods (fishes, shrimps, worms): Some of Diet – Not really necessary unless trying to condition a pair to spawn.
  • Vegetable Food: Some of Diet – They need very little. If there is no algae in the tank, you may feed vegetable food once in a while.
  • Meaty Food: All of Diet – Lean towards meaty foods in the shrimp category.
  • Feeding Frequency: Several feedings per day – As with all planktivores, feed at least 3 times a day.

Aquarium Care

These damselfish are hardy and easy to keep in a well maintained tank. Regular water changes done bi-weekly will also help replace the trace elements that the fish and corals use up. Guidelines for water changes with different types and sizes of aquariums are:

  • Fish only tanks:
    • Nano/Small tanks up to 40 gallons, perform 5% water changes bi-weekly.
    • Medium sized up to 90 gallons, perform 15% bi-weekly.
    • Large Tanks 100 gallons and over, once water is aged and stable, can be changed 10% bi-weekly to 20% monthly, depending on bioload.
  • Reef tanks:
    • Nano/Small tanks up to 40 gallons, perform 15% water changes bi-weekly.
    • Medium sized up to 90 gallons, perform 20% to 30% monthly depending on bioload.
    • Large Tanks 100 gallons and over, once water is aged and stable, can be changed 20% to 30% every 6 weeks depending on bioload.

For more information on maintaining a saltwater aquarium see: Saltwater Aquarium Basics: Maintenance. A reef tank will require specialized filtration and lighting equipment. Learn more about reef keeping see: Mini Reef Aquarium Basics.

  • Water Changes: Bi-weekly – Do bi-weekly water changes of 15% in a reef setting or 20% monthly in a fish only tank.

Aquarium Setup

The Domino Damsel can be kept in either a saltwater aquarium or a mini reef. They reach around 5 inches in length, but they are very deep bodied so need plenty of room to get around. Provide a tank that is at least 55 gallons or more for one Domino. Adults become very aggressive so other tank mates should be chosen wisely. If keeping a male and female pair, provide 75 gallons or more with plenty of hiding places.

Any substrate is fine, but provide a decor of rocks or coral that offer plenty of hiding places for shelter and retreat. Live rock with various hiding places, or even branching small polyp stony (SPS) corals, are ideal. Having many places to hide will reduce aggression between them and other fish in the tank.

There are no special requirements for water movement or lighting, unless they are housed with corals, in which case the coral requirements will need to be considered. Normal water temperatures between 72˚F to 82˚F (22 – 28˚C) and a pH from 8.1 to 8.4 will keep this damselfish healthy. Similar to clownfish, optimal spawning production occurs between 79°F to 83°F (26°C to 28°C).

  • Minimum Tank Size: 55 gal (208 L) – A 55 gallon tank is suggested for one specimen, 75 gallons or more for a pair.
  • Suitable for Nano Tank: No
  • Live Rock Requirement: Typical Amount
  • Substrate Type: Any
  • Lighting Needs: Any – It has no special lighting requirements, though if kept with live coral, they may need strong lighting.
  • Temperature: 72.0 to 82.0° F (22.2 to 27.8&deg C)
  • Breeding Temperature: 79.0° F – The optimal temperature for good quality eggs and larvae occurs with temperatures of 79° F to 82° F (26° – 28°C).
  • Specific gravity: 1.023-1.025 SG
  • Range ph: 8.1-8.4
  • Brackish: No
  • Water Movement: Any
  • Water Region: All – Will stay near a coral if present.

Social Behaviors

Domino Damselfish are aggressive, though when compared to some damsels like the Fiji Blue Devil DamselfishChrysiptera taupou, they may not seem so so bad. But still, they are aggressive. They are fine as juveniles, either in a school or alone,but as they grow older their attitude grows bolder and they become a dominant fish in the tank. It is best to keep just one per tank, unless it is a male/female pair.

Tank mates need to be as aggressive as the Domino’s are, or much larger. Peaceful and smaller semi-aggressive fish will be attacked as this fish ages to the point where the damsel takes over an entire community tank. If attempting to keep with smaller semi-aggressive fish, like dwarf angelfish, the tank should be at least 100 gallons with plenty of hiding place for the other fish.

In tanks under 100 gallons, it’s best to house them with triggerfish, large angelfish, butterflyfish, larger dottybacks or other species that can hold their own with aggressive fish. Do not house them with fish who can swallow them whole. It may be wise to avoid housing with any predatory fish, even if they are not big enough to eat the Domino Damsel. This is because of the Domino’s ability to recognize a predator, which may keep them from coming out and eating.

They will work great in a reef tank, and really pose no threat to corals. Their presence can actually benefit branching small polyp stony (SPS) corals. It helps if the coral is there from the start, as one aquarist noted that they added a coral frag and it was quickly attacked and shaken ruthlessly by a large male Domino Damsel guarding his eggs. Attempting to remove the frag resulted in the owner getting bit!

Domino Damsel, Dascyllus trimaculatus, with anemone
Photo courtesy: Joe D

In the wild, young Domino Damsels will often live in a commensal relationship with anemones like the one shown here. Adults share a commensal relationship with certain small polyp stony (SPS) corals.

Juveniles of this species are known to associate with 8 anemones in the wild:

Invertebrates are generally safe, though copepods and amphipods are eaten if present. If the tank is very large with a huge colony of established copepods, however, will they not be depleted. Be cautious with small ornamental shrimps, like the Sexy Anemone Shrimp Thor amboinensis, as they may be attacked.

  • Venomous: No
  • Temperament: Aggressive
  • Compatible with:
    • Same species – conspecifics: Sometimes – A male/female pair will need 75 gallons or more, with plenty of places for retreat in the rockwork.
    • Peaceful fish (gobies, dartfish, assessors, fairy wrasses): Threat – Domino Damsels are too aggressive for these fish.
    • Semi-Aggressive (anthias, clownfish, dwarf angels): Monitor – Domino Damsels are too aggressive for these fish, unless tank is 100 gallons or more.
    • Monitor – Six-line or Eight-line wrasses may be picked on, depending on the individual damsel and the tank size.
    • Large Semi-Aggressive (tangs, large angels, large wrasses): Safe
    • Large Aggressive, Predatory (lionfish, groupers, soapfish): Threat – Even a smaller predatory fish that cannot swallow them whole would make the Domino Damsel too afraid to come out and feed.
    • Threat – These fish are too slow, delicate, and peaceful to be kept with the Domino Damsel.
    • Anemones: Safe – Juveniles will live in a commensal relationship with a variety of anemones, though adults generally will not.
    • Mushroom Anemones – Corallimorphs: Safe
    • LPS corals: Safe – These damsels are beneficial to branching small polyp stony (SPS) corals.
    • SPS corals: Safe
    • Gorgonians, Sea Fans: Safe
    • Leather Corals: Safe
    • Soft Corals (xenias, tree corals): Safe
    • Star Polyps, Organ Pipe Coral: Safe
    • Zoanthids – Button Polyps, Sea Mats: Safe
    • Sponges, Tunicates: Safe
    • Shrimps, Crabs, Snails: Safe
    • Starfish: Safe
    • Feather Dusters, Bristle Worms, Flatworms: Safe
    • Clams, Scallops, Oysters: Safe
    • Copepods, Amphipods, Mini Brittle Stars: Monitor – Copepod and amphipods populations should be well established in a larger tank, or they can easily be diminished by the Domino Damsel.

Sex: Sexual differences

The opposite of clownfish, Domino Damsel males are larger and are the dominant fish in the group or pair. They are all born female and some females may have slightly undeveloped male organs to allow them to quickly turn into a male if the dominant male disappears.

Breeding / Reproduction

The Domino Damselfish have been bred in captivity and have been noted to spawn every 3 weeks. This follows the general pattern of clownfish. If breeding in captivity note that brittle stars, serpent stars, wrasses and crabs will eat the eggs of damselfish. The eggs and larvae are much smaller than those of clownfish, and are difficult to rear.

Successful breeding requires perfect water parameters and a large, non-predatory aquarium system. Domino Damsels, the opposite of clownfish, are born female and change to male as they move up the hierarchy. Similar to clownfish, optimal spawns are between 79°F to 83°F (26°C to 28°C). In typical Dascyllus genus fashion, the male chooses a spawning site which can be a rock, dead coral branch, coral rubble, or flat rock.

To attract a female, the male will engage in signal jumping and will produce sounds. Signal jumping is the behavior of dipping up and down quickly. Once the female sees that the male is ready to spawn, she will join him. They will then swim side by side, with the male slightly behind the female, or will swim at each other from opposite directions. Once they are side by side they both turn almost completely white, vibrate, then deposit their gametes. This spawning behavior is repeated every few minutes. Once they are done spawning, their regular color returns quickly as they swim away.

After the eggs are laid and fertilized, the male produces more pulse sounds as he defends the nest. One clutch can have over 1,000 eggs. The male will oxygenate the eggs and remove any that are undeveloped. He will viciously guard his nest until they hatch. The eggs will hatch in 2 to 2.5 days and then the larval stage lasts for 22 – 24 days (Wellington and Victor 1989). Due to similarities, see breeding techniques under Clownfish on the Marine Fish Breeding page.

  • Ease of Breeding: Difficult

Fish Diseases

Dascyllus are very durable damsels, even as juveniles. However there does seem to be an unexplained “sudden death” that damselfish can occasionally fall victim to. There are no signs, the fish is just dead one day. They can contract any normal disease that other saltwater fish are susceptible to. But it is pretty rare unless they are captured with an illness already in motion, so a quarantine period is a good idea.

Damselfish are susceptible to Marine Ich Cryptocaryon irritans, also called White Spot Disease or Crypt, Marine Velvet or Velvet Disease Oodinium ocellatum (Syns: Amyloodinium ocellatum, Branchiophilus maris), and Uronema disease Uronema marinum. All of these are parasites.

The most easily cured of these is Crypt (salt water Ich), but they are all treatable if caught in a timely manner. Marine Velvet is a parasitic skin flagellate and one of the most common maladies experienced in the marine aquarium. It is a fast moving that primarily it infects the gills. Uronema disease, which is typically a secondary infection, is very deadly and will attack your Chromis quickly and lethally.The first symptom is lack of appetite. It is most often contracted when the aquarist lowers the salinity to treat another type of illness, but doesn’t lower it far enough. This parasite thrives in mid-level brackish water salinity, which is a specific gravity of around 1.013 to 1.020.

Treat your new damselfish as gingerly as you would an expensive saltwater fish, and they will respond well. Anything you add to your tank that has not been properly cleaned or quarantined, including live rock, corals and fish can introduce disease. The best prevention is to properly clean or quarantine anything you want to add to the tank. For information about saltwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.


Domino Damselfish are inexpensive and readily available from pet stores and online.