The blue chromis (scientific name: Chromis cyanea) is a member of the damselfish family (Family Pomacentridae) that lives on coral reefs in the Western Atlantic Ocean and the Caribbean Sea.

Blue chromis. Source: ''Reef Fish Identification'', New World Publications © 1994.

Scientific Classification Kingdom: Animalia (Animals) Phylum:--- Chordata Class:------ Osteichthyes (Bony Fishes) Order:-------- Perciformes Family:-------- Pomacentridaedae (Damselfishes) Genus:----------Chromis Species:----------Chromis cyanea (Poey, 1860)

Physical Description

Blue chromis are small (7.5 to 15 centimeters in length) fishes with slender bright blue bodies and a forked tails with black margins. They have a black stripe running along the dorsal surface of the body and head.

Distribution

Blue chromis are found in tropical waters of the Northern Hemisphere (32°N to 10°N). They are found in the Western Atlantic, from Bermuda to southeastern Florida, the Caribbean Sea, and the Gulf of Mexico.

Habitat

Blue chromis typically live in the water column above coral reefs. Adults defend territories around a hole or a crevice in the rock where they hide from predators and sleep.

Feeding Behavior

Blue chromis are planktonivores who feed on plankton in of the water column.  They eat planktonic algae (more than half of their diet), zooplankton (primarily copepods), eggs, and larval stage fishes.  Only twenty percent of the diet of jeuveniles comes from planktonic algae and up to eighty percent of the diet of young adults comes from phytoplankton. 

They have good sensory vision that allows them to detect their small and often nearly translucent prey. They capture prey using their upturned protrusible mouth that extend, creating suction that draws in their prey.  They have closely-spaced gill rakers to stop the prey from escaping through the gills.

Behavior

Because blue chromis feed in the water column above the reef, they are at risk of predation while they are feeding.  Thus, blue chromis typically feed in large schools, and they are often observed feeding with other fishes such as creole wrasse or brown chromis. The fast swimming speed generated by their slender bodies and deeply forked tails allows them to move quickly so that they are able to escape strikes by predatory fishes. C. cyanea often hide in crevices in the reef when they are threatened.

Reproduction

Blue chromis reproduce year around with peaks occurring just before and after full moons from March through June. Spawning occurs in nests built on the sand, algae-encrusted coral, or rock walls. Several females lay eggs in the same nest and the eggs are vigorously defended for three days by the male until the eggs hatch. After hatching, larvae enter their pelagic stage which lasts from 27 to 34 days. 

Associations

Blue chromis often form schools with creole wrasse or brown chromis.

Conservation Status

Blue chromis are among the most common species of reef fishes in the Western Atlantic/Caribbean region, such that they are not deemed to be a species at risk.

References and Further Reading

• Encyclopedia of Life. Curator: C.Michael Hogan. 2011. Chromis cyanea (Poey, 1860)
• Fishbase. 2011. Chromis cyanea Blue chromis
• P.Humann and N.Deloach (Editor) 1994. Reef Fish Identification: Florida, Caribbean, Bahamas. New World Publications, Inc. Jacksonville, FL. ISBN: 1878348078
• N.Deloach. 1999. Reef Fish Behavior, Florida, Caribbean, Bahamas. New World Publications, Inc. Jacksonville, FL. ISBN: 1878348280