Chromis cyanea

Geographic Range

Blue chromis are found primarily in the western portion of the Atlantic Ocean, including the Gulf of Mexico and the Caribbean Sea, and extending to Bermuda and the Lesser Antilles (10-32°N).

• Biogeographic Regions
• nearctic nearctic
  • native native
• neotropical neotropical
  • native native
• oceanic islands oceanic islands
  • native native
• atlantic ocean atlantic ocean
  • native native

Habitat

Blue chromis are found in lagoons and reef communities at depths of 3 to 60 meters; they are found most commonly at depths of 10-20 meters, where food and shelter are most abundant. They prefer water temperatures of 21 to 27°C, the same parameters required for coral survival; healthy coral is of vital importance to this species, as reefs provide a location for feeding, breeding, and protection from predators. Males maintain small territories, typically comprised of a flat nesting area and an overhang or crevice with a small (approximately 7 cm in diameter) opening. They are also known to hide in fields of staghorn coral ( Acropora cervicornis ). Juveniles tend to school above and hide beneath or within a shelter-providing home structure, generally a coral head. They prefer yellow finger coral ( Madracis mirabilis ), Lamarck's sheet coral ( Agaricia lamarcki ) and smooth flower coral ( Eusmilia fastigiata ).

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• reef reef
• coastal coastal

Physical Description

Adults have an average total body length of about 13 cm (15 cm maximum). The body is compressed and oval in shape. These fish have a small, terminal mouth, continuous dorsal fin (12 dorsal fin spines and 12 dorsal soft rays) and deeply forked tail (2 anal spines and 12 anal soft rays). They are a bright, iridescent blue in color, with a black dorsal stripe and black margins on the dorsal fin, upper and lower lobes of the caudal fins, and front of the anal fin. They can be distinguished from similar species, such as juvenile black snapper ( Apsilus dentatus ) and blue hamlet ( Hypoplectrus gemma ), by their dark eyes and the continuation of their black dorsal stripe to the upper and lower margins of the tail. Males may exhibit any one of five color morphs, including dark grey-blue and light blue shades, with accompanying variations in dorsal stripe thickness. Sexual dimorphism occurs only during spawning, when females can be identified from light blue or dark-colored displaying males by their swollen bellies and protruding white genital papilla.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• sexes colored or patterned differently

Development

Blue chromis begin life as soft, translucent, demersal eggs, adhered to the substrate. The eggs are tended to by the male for 2 to 3 days before hatching into fast-swimming larvae. The larval stage lasts 17-47 days. These larvae stay within the cover of the reef surrounding the nest until they reach about 1 cm in length; they then join other juveniles in aggregations above the reef to feed on zooplankton. Juveniles, which have a more compact body shape than adults, school together until reaching 5-6 cm in length. After this they become sexually mature, at which point males begin to defend territories and maintain nests of their own.

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

Blue chromis are promiscuous, with multiple females visiting and laying eggs at many nests and males mating with multiple females. Male reproductive success may be determined by the condition and location of the nest, as well as the presence of eggs already in the nest.

To solicit females, males may perform a maneuver called a signal jump in which they rapidly propel themselves up vertically and then loop back to the starting position. They may also perform "dipping," where they swim in a zig-zag fashion above their territories. Males will present to females, swimming laterally and rotating 180 degrees for inspection. If a female indicates receptivity and the display is not interrupted, the male will lead her to his nest using an exaggerated side to side swimming motion. She will "nip" at the floor of the nest, and the male will respond by quivering his fins and skimming over the subtrate. He may nudge the female's genital papilla with his snout to encourage oviposition (known as butting). Once eggs are laid, a male will release milt (seminal fluid); it is not known precisely when the male releases milt, but it is hypothesized that it is dispersed by tail wagging. A male may begin to solicit another mate while one female is laying eggs in his nest. Spawning ends when the female is spent; she will either leave the nest immediately or be chased out. Other males may interfere in breeding, since displays take place up to 1 meter above a nest (outside territorial borders). Males may also sneak into nests while their owner is occupied in a display, preemptively fertilizing deposited eggs.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Female blue chromis have synchronized ovarian cycles and spawning occurs once a month, generally during the full moon. The spawning period lasts 3 to 7 days, during which time females both actively seek out males and are solicited. In most Chromis species, each clutch produced by a single female contains around 40,000 eggs. Eggs hatch into independent larvae within 2 to 3 days of spawning and are cared for by males. Juveniles reach sexual maturity within 47 days. Males maintain territories throughout the year, though increases in the number of larvae observed during the months of June and October indicate that reproduction may have a seasonal component.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • external external
• oviparous oviparous

Male blue chromis assume responsibility for all parental care, from nest preparation to caring for eggs. Small areas of sand, coral, or algae-covered rock are cleared by "nipping" (removing material orally) or generation of water currents by tail fanning. Males care for eggs and larvae by chasing away similarly-sized predators, nipping away debris, and moving water over the eggs.

• Parental Investment
• male parental care male parental care
• pre-fertilization
  • protecting
    • male
• pre-hatching/birth
  • protecting
    • male
• pre-independence
  • protecting
    • male

Lifespan/Longevity

Lifespan is estimated to exceed 5 years in captivity. Little is known about lifespan in the wild, although density-driven early mortality is thought to occur.

Behavior

Blue chromis are diurnal, feeding during the day and hiding at night. Juveniles often school and feed together in loose aggregations. Adult males are solitary and highly territorial. They perform distinct behavioral displays to maintain their territories, including chasing, pushing, butting, or ramming intruders out of nests, and swimming in parallel with neighbors to reinforce boundaries. These tactics may be accompanied by color changes, with brighter colors signifying aggression or dominance. If kept in captivity, dominance hierarchies develop; in small schools (less than six fish), individuals on the bottom of the social hierarchy may actually be harassed to death.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• solitary solitary
• territorial territorial
• dominance hierarchies dominance hierarchies

Home Range

Males defend territories that vary in size from 3 m^2 up to 20 m^2, extending upward from the substrate to about 1 m. Territory size is related to population density, with males in low density areas maintaining larger territories. Females swim and feed freely between and above these territories.

Communication and Perception

Blue chromis communicate mainly through visual channels. Interactions between competing males, residents and intruders, and potential mates are all marked by variations in swimming patterns and/or physical contact. Specific color changes often accompany behavioral patterns, providing the audience with additional visual clues and communicating intent. Blue chromis also use olfaction and mechanoreception (lateral line) to detect water movement and vibration, and can also hear using their well-developed inner ears.

• Communication Channels
• visual visual
• tactile tactile

• Other Communication Modes
• vibrations vibrations

• Perception Channels
• visual visual
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

Blue chromis feed mainly on plankton suspended in the water column. When feeding, they remain stationary in the water column and rely on the current to bring food particles to them. Feeding is accomplished by rapid extension of the jaw, which causes prey to be sucked into the buccal cavity, due to the negative pressure generated. Feeding is frequently interrupted when blue chromis dart for cover from a perceived threat. The threat of predation increases under conditions of low prey density, when these fish must distance themselves from protective structure in order to feed. Examination of the stomach contents of blue chromis revealed that their diet is composed of about 52% copepods and 34% tunicates by volume, with the remainder comprised of shrimp larvae, siphonophores, fish eggs, and ostracods. Juveniles may also eat planktonic algae.

• Primary Diet
• carnivore carnivore
  • eats eggs
  • eats non-insect arthropods
  • eats other marine invertebrates
• planktivore planktivore

• Animal Foods
• fish
• aquatic crustaceans
• cnidarians
• other marine invertebrates
• zooplankton zooplankton

• Plant Foods
• algae
• phytoplankton phytoplankton

Predation

As a moderately small reef fish, blue chromis are a food source for a variety of larger fish species. Predators can be resident or transient piscivores. To avoid predation, blue chromis hide under or within shelter and may also adopt a darker color morph when closer to the substrate, in order to camouflage their bodies.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Blue chromis share the reef habitat with many other species of planktivorous fish and are preyed upon by larger species of fishes. Juvenile black snapper ( Apsilus dentatus ), which feed alongside blue chromis, mimic them in order to attack unsuspecting crustaceans. The territorial nature of these fish may often reduce the number of hiding places for other similarly-sized non-territorial fish, such as brown chromis ( Chromis multilineata ), increasing predation rates on these species. There is no data currently available regarding parasites of blue chromis.

Economic Importance for Humans: Positive

Blue chromis are hardy inhabitants of saltwater aquariums and are common in the pet trade.

• Positive Impacts
• pet trade pet trade

Economic Importance for Humans: Negative

There are no known adverse affects of blue chromis on humans.

Conservation Status

Blue chromis are abundant throughout their geographic range, and are listed as a species of least concern by the International Union for the Conservation of Nature and Natural Resources.

Additional Links

Encyclopedia of Life

Contributors

Natasha Perrine (author), Indiana University-Purdue University Fort Wayne, Mark Jordan (editor), Indiana University-Purdue University Fort Wayne, Jeremy Wright (editor), University of Michigan-Ann Arbor.

References

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