The Blue-green Chromis is peaceful, even as an adult, and can be kept with many other community fish!

The Blue-green Chromis Chromis viridis is considered an excellent choice for the marine or reef aquarium. This is a damselfish that is appreciated for its beauty, peaceful yet active nature, and its durability. Being inexpensive and almost always available from a marine fish supplier, beginners and experienced aquarists alike can enjoy this fish.

You will notice that they have slight color variations from a pale green to a light blue. Thus they are also known as the Green Chromis or Blue Green Damselfish. Mature males in a nesting mood can also be yellow. Growing to only about 3 3/4 inches (10 cm) in length, they can be kept singly in a smaller aquarium or as a group in a moderately sized tank. They are often confused with the Blackaxil Chromis Chromis atripectoralis, who are similar in color but will grow to an inch larger. The Blackaxil also has a dark, muted gray spot at the base of their pectoral fins.

These are a wonderful schooling fish and in the wild are found in large shoals numbering into the hundreds. This grouping has been described as a living curtain! Chromis do not form bonded pairs in the wild, rather several males and females will breed with one another. Males will prepare and guard the nest until the eggs hatch.

Despite being designated as a true damselfish, the Blue Green Chromis have a peaceful demeanor. They can be kept with almost all other peaceful community fish as well as invertebrates and corals. They can be kept singly, but will do best in a group of 6 or more. Because they will develop a hierarchy, keeping fewer than 6 fish will leave the “low man on the totem pole” vulnerable to aggression.

The beautifully colored and peaceful Blue Green Chromis are moderate to moderately easy to keep. They can reward you with an interesting display in the aquarium for years to come, yet they are probably one of or the most delicate of the Chromis Genus.

They need good water quality, the proper numbering of a group, and tank mates that are peaceful and selective semi-aggressive. They will eat anything you offer, but the staple should be good quality meaty foods with a little veggie flake here and there. Being planktivores, they do need to be fed at least 3 times a day. Chromis like the upper parts of aquariums but do appreciate branching SPS corals to hide in, though artificial versions are often accepted.

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: Chromis
  • Species: viridis
Blue-green Chromis – Quick Aquarium Care
  • Aquarist Experience Level: Beginner
  • Aquarium Hardiness: Moderately hardy
  • Minimum Tank Size: 30 gal (114 L)
  • Size of fish – inches: 3.9 inches (9.98 cm)
  • Temperament: Peaceful
  • 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 Blue Green Chromis Chromis viridis was described by Cuvier in 1830. They are found in the Indo-Pacific from the Red Sea to the Line Islands, Marquesan Islands and the Tuamoto Islands, then northward to the Ryukyu Islands and south to the Great Barrier Reef and New Caledonia. This species is not listed on the IUCN Red List of Threatened Species. Other common names this species is known by include Green Chromis, Blue Green Damselfish, Blue-green Puller, Green Puller, and Blue Puller.

This species is a member of the very large Pomacentridae family of Damselfish and Anemonefish. It belongs to the subfamily Chrominae in the Chromis genus, which is the largest group of fish in the family. There are currently 100 recognized species in this genus, though not many are collected for the aquarium trade.

The Chromis species are more streamlined than others in the family, and have a deeply forked tail. This tail fin provides them with the ability to swim fast and furious with their shoal or away from predators. The Chromis also have an orbital papillae, small rounded protuberances on the back and bottom edges of the eye’s orbit. This is found on other zooplanktivores as well, such as anthias, and is thought to help reduce turbulence as they swim.

Chromis are less aggressive damselfish and they will get along well with other individuals of the same species as well as with other species of fish, corals and invertebrates. They are just about as hardy as their close relatives, but are more of a schooling fish. Many species feed mostly on planktonic crustaceans in the water column, but can exhibit seasonal changes to their diet, and feed heavily on filamentous and floating algae as well.

The Blue Green Chromis prefer sub-tidal reef flats and lagoons from depths of 5 to 39 feet (1.5 to 12 m) They are typically found in large schools that can number into the hundreds. They hover above branching corals, especially Acropora, in which they take shelter and sleep in at night.

To feed they face the current, which provides them with planktonic foods like copepods, shrimp larvae and amphipods, as well as polychaetes, fish eggs and fish larvae. During the summer, near Okinawa, Japan, they switch to more of an omnivorous diet, eating large amounts of phytoplankton, filamentous algae and zooplankton.

Blue Green Chromis have been bred in captivity, though the larvae is very hard to sustain.

  • Scientific Name: Chromis viridis
  • Social Grouping: Groups – Typically found in very large schools numbering into the hundreds.
  • IUCN Red List: NE – Not Evaluated or not listed


The Blue Green Chromis has a compact, slightly deep and slender body with a deeply forked tail fin. Their structure makes for quick getaways and helps in keeping up with the large schools they swim in. They can reach up to 3 3/4 inches (10 cm) in length, though typically only grow to about 3 1/2 inches. Males and females are the same size. In captivity they have been known to live from 8 to 15 years, although in the wild the typical lifespan is 3 to 8 years.

Their color ranges from an intense green to a bluish green, depending on the lighting. The only other color they have is a silvery white area under the eye. During spawning the male will change to yellow, or a muted greenish yellow.

There are a couple of similar looking Chromis species. One that looks almost identical to the Blue Green Chromis is the Blackaxil Chromis Chromis atripectoralis. it is almost an inch larger, however and it also has a dark spot at the base of the pectoral fins which is absent in the Blue Green Chromis. This spot is not an obvious black dot, but is more of a muted gray coloring.

Another similar looking Chromis is the Yellow Edge Chromis Chromis multilinieata which originates from the Caribbean down to Brazil. It has a similar shape but grows much larger, reaching 6.7 inches (17 cm) in length. Its body can have a muted greenish-yellow to tan color with yellow on the tips of the dorsal fin. It also has a prominent black spot at the pectoral fin area. Some aquarists have added these to their school of Blue Green Chromis for an interesting contrast with no aggression issues.

  • Size of fish – inches: 3.9 inches (9.98 cm)
  • Lifespan: 15 years – In the wild their life span is 3 to 8 years, but in captivity, they have been known to live from 8 to 15 years.

Fish Keeping Difficulty

The Blue-green Chromis is among the easiest of all marine fish to keep. They are moderately hardy and great for beginner saltwater hobbyists who are dedicated to providing good water quality. They are more susceptible to illnesses due to poor water quality and improper tank mates, however, when compared to others in the damselfish family. Doing normal water changes, feeding them a variety of foods several times a day, and having proper tank mates will keep your Chromis living a good long life.

They are peaceful as far as damsels are concerned. You can keep either a single fish or a group of six or more along with other peaceful community fish. With their more docile nature they are more likely to be picked on themselves by certain more pugnacious peaceful fish, as well as semi-aggressive and aggressive tank mates. Any fish that is picked on and harassed is also more likely to become sick. If they are staying in one spot in an upper corner, it is most likely due to aggression from another fish, and they should be removed.

  • Aquarium Hardiness: Moderately hardy
  • Aquarist Experience Level: Beginner – They can be kept by a dedicated beginner devoted to maintaining water quality.

Foods and Feeding

The Blue-green Chromis are omnivores. In the wild, They are primarily planktivores, though in some waters during summer months they will feed on filamentous and floating algae. The water column provides them with planktonic foods like copepods, shrimp larvae and amphipods, as well as polychaetes, fish eggs and fish larvae. The males will also feed on eggs in their nest if they are infected.

Provide variety in their diet that includes meaty foods such as mysis shrimp, enriched brine shrimp, other finely chopped shrimp or fish, and some flake for herbivores on occasion. They will feed in the water column and at the top of the tank. If feeding pellets, make sure they are wet before adding so air will not get into their digestive tract, which can cause issues.

It is best to feed small amounts several times a day. Typical of planktivores, these fish eat constantly in the wild, so they should be fed at least 3 times a day.

  • Diet Type: Omnivore – In the wild they primarily feed on planktonic crustaceans in the water column, but will vary their diet at times to include various types of algae.
  • Flake Food: Yes – Flake food for herbivores on occasion.
  • Tablet / Pellet: Yes – Wet the pellets down with tank water before adding to prevent air from getting trapped in their digestive tract.
  • Live foods (fishes, shrimps, worms): Some of Diet – Live foods that are gut loaded are a great way to induce spawning.
  • Vegetable Food: Some of Diet – They need very little.
  • Meaty Food: Most of Diet
  • Feeding Frequency: Several feedings per day – As with all planktivores, feed at least 3 times a day.

Aquarium Care

These damselfish are moderately hardy and fairly easy to keep in a well maintained tank. Poor water quality will result in illness and disease with these, as well as any saltwater fish. 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 Blue-green Chromis can be kept in either a saltwater aquarium or a mini reef. These fish do best with a minimum tank size of 30 gallons (114 liters) for one fish. If keeping as a shoal of 6, provide at least 55 gallons, and then increase the tank size if the number in the school increases. Keeping fewer than six results in the smallest becoming targets of aggression in the pecking order, leading to death. The next in line will follow in attracting this aggression, and so on.

A saltwater aquarium well decorated with rockwork or corals will provide many places for retreat. In the reef, creating a decor of live rock and either Small Polyp Stony (SPS) branching corals, or rocks and “artificial” Acroporas in a fish only aquarium, help them feel secure and give them places to shelter and sleep. Chromis like the upper parts of aquariums, so make sure there is plenty of open area at the top of the tank for them to swim.

Any substrate and lighting will do, but may depend on the needs of any coral present. Some areas with algae growth are appreciated if they feel the need to nibble. Water movement is also not a significant factor, but the temperature should be between 72˚F to 82˚F (22 – 28˚C), with pH from 8.1 to 8.4. Similar to clownfish, optimal spawning production occurs between 79°F to 83°F (26°C to 28°C).

  • Minimum Tank Size: 30 gal (114 L) – A 30 gallon tank is suggested for one specimen, though 15 gallons can work if this is the only fish to be kept. 55 gallons is recommended for 6, and increasing the tank size with the school size.
  • Suitable for Nano Tank: Sometimes – A minimum 15 gallon aquarium will work if this is the only fish to be kept.
  • Live Rock Requirement: Typical Plus Hiding Places – They need crevices to hide in. Rock work, live rock, and live or “artificial” small polyp stony (SPS) branching corals help them feel secure.
  • 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: Top – They like the upper areas, but will inhabit the middle areas of the tank when there is not enough open space near the top.

Social Behaviors

The Blue Green Chromis are the exception to the rule for damsels when it comes to aggression. They are relatively peaceful, even into adulthood, and can be kept together with most any other community fish. They can be kept either as one or as a school of 6 or more. If keeping just one, do not keep it with aggressive or the more boisterous semi-aggressive fish that feed on the same foods, or the Blue Green Chromis will be picked on.

Keeping a school is an excellent choice for larger aquariums. These damsels make a great display of flashing greenish blues near the top of the tank. In captivity they form a hierarchy, however,  and experts strongly agree if keeping a group there should be at least 6 or more to even out aggression in the pecking order. Keeping lower numbers typically results in the smaller and weaker ones being picked on, causing stress and eventually death..

When keeping them in a community they will do well with certain semi-aggressive fish like the more peaceful tangs, but do not keep them with anthias or aggressive pygmy angelfish. Larger semi-aggressive fish are okay, but only in larger tanks with the least aggressive of the fish. For example some triggerfish are relatively mellow, like the Niger Trigger, but more aggressive triggers will go after the Blue Green Chromis. The same holds true for tangs or surgeonfish. Do not house them with any sized aggressive fish or larger fish that would swallow them whole. A Chromis staying near the top corner of a tank is an indication it is being bullied. Either remove the bully or the Chromis.

They are great in a reef tank and will not bother any corals. They do enjoy the safety of the branches of any Small Polyp Stony (SPS) coral you may have. They “sleep” in the branches of SPS corals and their fin movements help to remove and prevent detritus from getting in the coral’s crevices. This in turn promotes the health of any live SPS branching coral by minimizing detritus build up, which kills polyps.

They are no threat to corals and most invertebrates, including mature copepods and amphipods. They will however, feed on any floating larvae or planktonic invertebrates from spawns that occur in a healthy tank.

  • Venomous: No
  • Temperament: Peaceful
  • Compatible with:
    • Same species – conspecifics: Yes – Keep in groups of 6 or more to spread out aggression.
    • Peaceful fish (gobies, dartfish, assessors, fairy wrasses): Safe – In larger tanks they are also safe with other Chromis and Spinecheek Damselfish that are more peaceful.
    • Semi-Aggressive (anthias, clownfish, dwarf angels): Monitor – Do not house with anthias, as they are aggressive toward fish that compete with them for food in the water column. Aggressive dwarf angelfish should also be avoided.
    • Threat – Do not house them with any aggressive fish.
    • Large Semi-Aggressive (tangs, large angels, large wrasses): Monitor – Large groups of these Chromis may be kept with the less aggressive species of these fish. But avoid the more aggressive species of the large wrasses, tangs, puffers, triggerfish or angelfish.
    • Large Aggressive, Predatory (lionfish, groupers, soapfish): Threat
    • Threat – Seahorses and Pipefish should only be housed in their own environment. Mandarins may be fine in a very large, mature tank with live rock that has plenty of copepods. Blue Green Chromis generally will not bother them.
    • Anemones: Safe
    • Mushroom Anemones – Corallimorphs: Safe
    • LPS corals: Safe
    • SPS corals: Safe – They will use any branching small polyp stony (SPS) coral for protection and when sleeping at night. This will help keep detritus away from the SPS crevices due to movement of their fins.
    • 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: Safe

Sex: Sexual differences

Males and females are the same color and size, yet differences can be seen when the males change to a more yellow color during spawning.

Breeding / Reproduction

These fish have been bred in captivity and aquarists have noticed that their Blue Green Chromis spawn every two weeks. They will use the wall of the tank if no other area is available. 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 clownfish, and are difficult to rear.

Successful breeding requires perfect water parameters and a large, non-predatory aquarium system. All Chromis species are similar to clownfish, which have optimal spawns between 79°F to 83°F (26°C to 28°C). They are known to scatter their eggs over the nesting site, or what is referred to as an algae mat. This area consists of sand, rubble, or a piece of sponge.

The male sets up his territory on the sea floor under, or to the side of, the school of Blue Green Chromis. He enters the group and circles a female. If she is in breeding mode, she will follow him back to his spawning site. He will rub his genital papillae on the algal mat and the female will mimic his behavior and lay her eggs. The male will repeat this behavior with another females until his nest is full.

The eggs are 0.6 to 0.66 mm in length and 0.42 to 0.49 mm in width. These little eggs attach to the algal mat with small stalks. The male will then guard his nest, keeping the eggs ventilated and protected. He will also feed on any eggs that go bad so they do not contaminate the rest of the clutch. Eggs hatch within 2 to 3 days, depending on the water temperature. The larval stage lasts from 17 to 47 days. The eggs and larvae are much smaller than with clownfish, and are difficult to rear. Due to similarities, see breeding techniques under Clownfish on the Marine Fish Breeding page.

  • Ease of Breeding: Difficult

Fish Diseases

The Blue Green Chromis are one of the most delicate of all the Chromis species, and do not do well when handled poorly. Unlike other damsels, they are sensitive to poor water conditions and their water needs to be monitored and tested to rule out any ammonia, nitrite or high nitrates, especially during quarantine.

Poor water quality makes Chromis very susceptible to several bacterial infections and/or viruses. On the up side, they tend to be some of the first fish to show there is a problem within the tank. They also will succumb to disease if being harassed by other fish or when in a school with their own kind, if the school is too small. When one fish gets sick, others can be infected. The skill is in providing proper housing, good water quality, and proper tank mates.

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 fast moving and primarily infects the gills. Uronema disease, which is typically a secondary infection, is very deadly and will attack your damselfish 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 Chromis 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 diseases. The best prevention is to take care 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.


The Blue Green Chromis are moderate in price and readily available from pet stores and online.


 Blue-green chromis (Chromis viridis) (Image Credit: Rickard Zerpe, Wikimedia Commons CC BY-SA 2.0 Generic)