When saltwater aquariums started their popularity in the 1970s, the aquaria were usually designed as reefs, since reefs are the homes of the most colorful and available fish. This meant sand and coral. The balance of salinity, specific gravity and temperature of a reef aquarium are set to mimic the reef waters.
The first fish that was usually introduced to the reef tank was a blue damsel, because this was an inexpensive and hardy fish which would balance the chemical environment with its eating and excreting habits. Now this stabilizing effect is often gotten from the blue/green chromis, of the same damselfish family. Its shimmering color ranges from soft blue on the dorsal (top) side, to a pale green belly, and it is a striking addition to the white sand and coral. Changes in lighting appear to change the colors of this fish. There is also a green chromis which is similar (obviously more green) that has a black spot at the base of the pectoral (side) fins.
The scientific name for the blue/green chromis is Chromis viridis. Common names are mixtures of blue, green, chromis, damsel and damselfish. It is found in the Indo-Pacific and African regions, including Fiji, Melanesia and Tahiti. It usually arrives in a reef tank at about one inch, growing no longer than three inches in a tank, four inches in the wild, and costs between two and four dollars. This omnivore is passive and gentle and lives in schools in lagoons. Because of its small size, a school of five to ten in a tank is a striking vision.
Chromis are more peaceful and less aggressive than other damselfish and anemone fish, though they are members of the same family, Pomacentridae.. While they use the entire tank, they tend to school in the upper areas, which tends to draw out other fish who are normally more shy. Also found in the Red Sea, these fish will live eight to fifteen years even in fish tanks. They get along with virtually any non-predatory fish and are excellent specimens for the beginning aquarist. One can live comfortably in a ten-gallon tank, although thirty gallons is the recommended minimum. They are safe around reefs, corals and invertebrates.
A native to mid-depth reefs and shallow lagoons, the chromis will meander all over the aquarium. In the wild, they will school in large shoals of branching corals like Acropora. It will nestle down in coral to sleep at night or if frightened. At other times, they relish as much room as the tank will offer to nourish their open water swimming habits.
As an omnivore, the chromis will thrive on several feedings throughout the day of meaty foods, herbivore flakes and frozen preparations. To maintain the coloration, be sure the foods are vitamin-enriched.
Once the chromis is acclimated and the aquarium is stable, choices to add to the tank are wide open – live invertebrates, more chromis, live coral, and any marine fish that is not predatory. Shrimp, sea anemones, and clown fish would be welcome.
No one is sure how to determine the sex of a chromis, but they have been known to breed in captivity. When ready to breed the male will turn a pale yellow, and there should be four females to each breeding male. But the water must be perfect, and the tank must be as large as possible, with no predators.
This fish is so lovely and its schooling so fascinating that breeding may just be a waste of time – they are readily available and inexpensive.