Green Chromis – A Complete Guide (Care, Diet, Facts)

One of the joys of keeping a salt-water aquarium is in the variety of species owners get to watch and care for. The fish, coral, and plant life can present a dazzling array of diverse colors, shapes, and behavior. For many enthusiasts, designing their marine environment is akin to creating living art, and is a joy for experienced owners and novices alike.

As a brightly colored, swift and active schooling fish, the green chromis makes an excellent addition to nearly all tanks. The one caveat for ownership stems from their personality. They are a passive, peaceful fish, meaning that owners should avoid placing them with more aggressive species. Otherwise, the chromis is compatible with nearly all other aquarium setups.


Overview of Green Chromis

Green Chromis are a species of damselfish, one of approximately 300 members of this family of salt-water fish. Damselfish species are generally characterized for their brightly colored appearance, and members of chromis sub-genera are no exception. The green chromis is the most commonly sold and owned of the chromis species, and is easily identified by its bright, flashing colors.

The Green Chromis (Chromis Viridis, also known by other names including Blue-Green Chromis and Reef Chromis) is native to shallow reefs in the Indian-Pacific and South Pacific oceans.

A second species of chromis, the black axil chromis (chromis atripectorialis), closely resembles the green chromis in size, shape, and coloration, A small black circle at the base of its pectoral fin allows it to be distinguished from its cousin, the green chromis.

Their colorful looks are one of several reasons why salt water tank owners consider them an attractive fish. Other factors for the popularity of the green chromis include their temperament, good overall health, and schooling behaviors. Unlike many damselfish, chromis are mild-tempered and non-territorial, outside of spawning times. Whether you are a novice tank owner or an experienced salt-water aquarium enthusiast, the green chromis is a suitable and attractive fish for all owners. They will add color and dynamic movement to your tank environment, and co-habitate well with other aquatic species that you might keep in your tank.


Green chromis is a small but striking aquarium fish. They can grow up to 4 inches in length, and their bodies are tall relative to their height, giving them a lean and streamlined appearance. Their tail fin, or caudal fin, is sharply notched. A single dorsal fin rises along much of the length of their back.

Their name offers a generally accurate description of their coloration. Their scales are a vibrant green, tinged with blue, and will shift to different shades depending on the lighting of your tank. Yellow and white might also be present in their scales. The males in particular may develop more yellow hues as they mature.

From top to bottom, they are a slender fish, which gives them an agile and graceful appearance as they swim. Their scales are highly reflective, and tank owners will enjoy getting flashes of bright light from them as the chromis school moves throughout the tank.


Damselfish have a reputation for aggression, often as a by-product of their territorial instincts. The Green chromis is one of the exceptions in this family of colorful fish.  They prefer to congregate in schools and cruise the reef, without attempting to claim specific territories for themselves. These schools, which can form with as few as six fish, swim at all levels of the water column in your tank. This means the strikingly colorful green chromis is a highly visible and active resident of nearly any size of tank.

Green chromis are generally a peaceful species, especially towards other tank inhabitants. This includes different fish species, invertebrates, corals, or other specialty species. Within their schools, there can be minimal conflict as they establish their own hierarchy. A dominant fish will assert itself over the rest, and get first choice of food.

With fewer than six fish, the dominant, alpha fish may be prone to bullying behavior towards other, more passive chromis. To ensure that none of the tank inhabitants experience unnecessary stress, experts recommend keeping at least six green chromis in your school. The more fish there are in the shoal, the more the alpha’s attention or aggression will be divided within the group.

Breeding and Reproduction

During breeding times, levels of aggression may rise somewhat both within the school and towards other members of the tank. Within the shoal, this is due to competition for mating partners. Some individuals may challenge the alpha in the established hierarchy, but conflict is more a matter of harassment than attacking and fighting. The chromis, however, do not form pair bonds when mating. This also helps to minimize tension during mating periods within their schools

If there is hostility towards other tank inhabitants, it is generally over preferred egg-laying locations in the sand or on coral features. As in other damselfish species, the males take responsibility for preparing and guarding the nest. The territorial nesting period is brief, and the fish should quickly resume their regular conduct.

Reports from scientists and hobbyists alike agree that it is extremely difficult to ensure the survival of any eggs that happen to hatch. According to anecdotes shared online, there is some chance of survival for the fry if the owner is attentive to all water conditions, as well as providing the correct nutrition. The green chromis fry need zooplankton and phytoplankton to develop, just as they would in the wild. Even so, a 5% rate of survival for captive chromis fry is considered lucky.

Any competition for dominance within a shoal is generally minimal. Should you notice an isolated fish that seems to be avoiding the rest of the school. The mild temperament of the green chromis makes the species an excellent tank companion for nearly any aquarium set-up.


The relatively high activity of the chromis means that they do best with constant, regular feeding. They can be omnivorous, meaning they will consume organic matter from both plants and animals. However, they will do best with a diet that is predominantly meat, as it matches their food source in the ocean. Most owners and aquatic pet experts recommend providing food for the chromis three times daily.

In the wild, green chromis prefer to face the current and take phytoplankton as food as it drifts past them. They will scavenge as well, eating mysis shrimp, eggs, and larvae. In an aquarium setup, most food that is tailored to carnivorous fish will suit them. This will include mysis shrimp, frozen cubes of various proteins, and even flakes or pellets. Brine shrimp is another favorite, but owners should search for a vitamin-enriched variety, as brine shrimp often do not provide much nutritional value on their own.

In general, vitamin-enriched food should help them to retain the vibrancy of their appearance, in addition to their overall level of health.  Liquid vitamins will also serve this purpose, and may be easier for owners to incorporate into their tank feeding schedule.

For their size, they are considered a rather voracious and indiscriminate eater by owners, and are often the first fish to swarm to food at feeding times. They still do best with a well-selected diet. For this reason, owners may even want to incorporate algae into their meals, which would form part of the matter they consume in the wild as it drifts past on the current.

Tank Care

The relatively robust health of the green chromis means that it can thrive in most tank environments, with a life expectancy of 8 to 15 years. This lifespan, of course, will vary from tank to tank, and fish to fish. Owners will want to check the condition of their tank prior to introducing the chromis to its new environment. A few items of consideration include the temperature and pH of the tank, carbonate hardness, the recent and observable health of other organisms in the tank, and any water treatments or medications that might have been recently used in the aquarium.

The preferred tank conditions for green chromis are all within the range of those preferred by most tropical saltwater fish, coral and invertebrates. Temperatures between 20 – 22 degrees C, or 72-80 degrees F, will be optimal. This is a fairly wide range, but anything higher or lower will affect the activity and behavior of the fish, and eventually even their health.

A pH range of 8.1 – 8.4 is recommended by experts and pet stores. Ideal carbonate hardness in your tank is within a 8 – 12° dKH range.The gravity, or salinity level, should be between 1.02 – 1.025. When introducing the chromis to your tank, take caution to test for nitrites, nitrates, and ammonia, as they will be sensitive to those. Have an understanding of these measurements, along with the equipment to properly monitor and maintain them.


Not maintaining these conditions may allow bacteria or parasites to develop within the aquarium environment. While hardy, the green chromis is still as susceptible to these as any other fish would be. Excessive stress, which may stem from harassment by other species, will weaken their natural defenses as well.

Chromis will be among the first of a tank’s members to succumb to any foreign pathogens, and many bacteria and parasites spread quickly within the tank. Given that you are paying attention to the right signs, you should be able to identify treat most issues in time. Lack of appetite is often the first sign of other health issues, so be sure to monitor their behavior and eating closely. If you have concerns, check for abnormalities around the gills, eyes, and fins, and act quickly, as most conditions are treatable if caught in time.

Common parasites or ailments for the blue-green chromis include Marine Ich, Marine Velvet, and Uronema disease. These can all be treated relatively easily by a proactive and observant owner. Check with local aquatic pet stores, veterinary offices, or internet suppliers for reliable antibiotics and water treatments.

Aquarium Setup

The green chromis will do best in a tank environment that replicates their natural habitat. Although they are a schooling fish, they prefer to do so around the safety of reefs, which provide both refuge from predators and places for their eggs. They are coral safe, but do not require living coral, which will simplify tank upkeep for novice owners.

Both large polyp stony coral (LPS) and small polyp stony coral (SPS) are compatible with the green chromis. The vibrant colors of the chromis will be highlighted against the living corals, and will encourage the shoal to explore their surroundings. Coral also act as water filters, so tank owners will have to refresh their water less frequently.

A tank of at least 30 gallons is the minimum recommended size for them. This allows the chromis to have ample room to school and explore the features you provide for them.

The Fish For You?

The green chromis, or blue-green chromis, adds color and personality to any aquarium. The vibrant appearance and curious, active personalities make them highly visible. Their social, schooling behavior further highlights their presence in your aquarium. Be sure to keep at least five in any given tank. You may find that their social nature encourages other fish in the community to shoal with them.

Some owners recommend including larger, more moderately aggressive fish in your tank with the chromis to reinforce their shoaling personalities. Without a more dominant fish, there may be squabbling within the group over the hierarchy.

It also helps that they are an affordable fish, and can be found at most pet and fish stores for under ten dollars. Additionally, as smaller fish, they require less food. Unlike many less-expensive fish, they are healthy and long-lived, often surviving 8-15 years if cared for properly. Not every individual will have the same lifespan, so owners should expect to add fish to the shoal in order to maintain the minimum of five.

With an assortment of live rock, coral, and plant features, the green chromis should feel right at home after being added to the tank.

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