Damselfish (Scientific name: Pomacentridae) are among the most beautiful and common reef fishes. Small and brightly colored, they are one of the most abundant and widely-studied families of tropical reef fishes — are popular aquarium fish too. The Damselfish subfamilies within the family Pomacentridae are Abudefdufinae, Chrominae, Lepidozyginae, Pomacentrinae, and Stegastenae. [Sources: Wikipedia and Monica Weinheimer, Animal Diversity Web (ADW) /=]
Pomacentridae is a family of ray-finned fish, comprising the damselfishes and clownfishes. consists of approximately 28 genera and 335 species. They tend to be territorial and can be aggressive, although this is not the case for the non-territorial, free-swimming planktivores or the clownfish and anemonefishes (Amphiprion and Premnas) that live with anemone hosts (See Separate Article on Clownfish).
Damselfishes are largely herbivorous, sometimes tending “gardens” of filamentous algae, but may eat tiny invertebrates. Damselfishes display a wide a range of reproductive behaviors, including polgamy, promiscuity, polyandry and monogamy.
There are fossil records of pomacentrids from the Lower Tertiary Period (66 million to 56 million years ago) and Lower Eocene Period (56 million to 47.8 million years ago). Little is known about the lifespan of damselfish. Eupomacentris spp. live an estimated six to eight years. Some species may live 10 to 12 years in the wild and perhaps 18 years in captivity.
In aquarium settings damselfish can be aggressive, but are extremely hardy. As a rule damselfish are not consumed as food but in some areas on the Indian Ocean people eat one that they catch in traps or with hooks. Three damselfish species — Chromis sanctaehelenae, Stegastes sanctaehelenae, and Stegastes sanctipauli — are listed as vulnerable according to the World Conservation Union, 2002) /=\
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Damselfish Habitat and Where They Are Found
Damselfish live in temperate and tropical, saltwater marine environments. throughout the world, with the majority of species occurring in the Indo-west and central Pacific region. They can be found off the coasts of Asia, Sub-Sahara Africa, Australia, tropical South America and oceanic islands and in the Indian Ocean, Atlantic Ocean and Pacific Ocean. [Source: Monica Weinheimer, Animal Diversity Web (ADW) /=]
You can typically find damselfish in reefs, other coastal areas, brackish water and relatively shallow sea bottoms. Some live along steep edges of the reef, and others in sandy sheltered lagoons. In each ocean a few species occupy warm temperate waters, and three estuarine species can sometimes be found in fresh water. Some live on rocky areas or sea-grass beds, some school in the water column. A few deep-water species occur at the edge of continental shelves at depths below 100 meters (328 feet), but most damselfish occupy shallow water between two and 15 meters (6.5 and 49 feet) deep.
Damselfishes are numerous and common on tropical reefs, and often play important roles in the ecosystem and habitats where they live. Many of them affect the growth of algae on the reef, encouraging algal growth in some areas while using the algae as a food source. Some groups of juvenile damselfishes clean other fishes. sea anemones
Damselfish Physical Characteristics
Damselfish are cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature) and have bilateral symmetry (both sides of the animal are the same). Sexual dimorphism (differences between males and females) is common. Among most damselfish groups males and females differ externally only in the form of the urogenital papilla (an anatomical feature of external genitalia). [Source: Monica Weinheimer, Animal Diversity Web (ADW) /=]
Damselfish range in size from five to 36 centimeters (two to 14 inches, with most specimens less than 30 centimeters (a foot) long. Both sexes are roughly equal in size and look similar. Sometimes females are larger but most of time males are larger. Sexes may be colored or patterned differently with the male being more colorful.
According to Animal Diversity Web: Damselfish “bodies tend to be high, oval and laterally compressed, with the lateral line interrupted. The single, continuous dorsal fin has eight to 17 spines and 10 to 18 soft rays, the anal fin usually has two spines (occasionally three), and the caudal fin is typically forked. Adults of many species have filamentous extensions on all but the pectoral fins.
Ctenoid scales are present on the body, head, and unpaired fin bases. Damselfish, with a few exceptions, have one rather than two nostrils on each side, and a small mouth. The palate is toothless, and the floor of the mouth contains a pharyngeal plate (a triangular fused tooth plate). Teeth may be arranged in one or two rows and may be incisorlike, especially in territorial forms that graze on algae, or conical, often seen in forms that live in the water column and catch small organisms.
Some damselfish are bright colored. Plankton eaters are typically more having brightly colored while algae feeders are duller shades of orange and brown. Damselfish also display makings and signals in ultraviolet light. The azure damsel fish can see in both visible light and ultraviolet light. In visible light it is blue and yellow. In ultraviolet light the blue looks white and the yellow looks black. [Source: Great Barrier Reef.com]
Coloration of adult damselfishes ranges from brilliant to drab and can vary with mood and time of day. Juveniles, especially in the territorial (defend an area within the home range), bottom-dwellers, often possess different, brighter colors than adults of the same species. One of the more colorful species is the large orange Garibaldi, which inhabits the coast of southern California and the Pacific Mexican coast. [Source: Monica Weinheimer, Animal Diversity Web (ADW) /=]
The majority of damselfish assume sex-specific colors during spawning. Usually the male, but sometimes the female (and sometimes neither), assumes courtship colors, the pattern and intensity of which vary according not only to species, but also to geographic and perhaps other factors.
Damselfish are diurnal (active mainly during the daytime), motile (move around as opposed to being stationary), territorial (defend an area within the home range), social (associates with others of its species; forms social groups), and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates).
Damselfish are surprisingly territorial for their size and diverse coloration. They typically stake out a designated “home” amongst the coral reef which they will then defend with their lives often against predators much larger than themselves. [Source: Great Barrier Reef.com]
Most damselfish stake out territories on patches of reef in sheltered areas where they hide, feed and spawn. Males aggressively defend these territories, allowing thick algal growth that provides them a primary food source. They prune algae gardens they carefully maintain, even removing intruding sea urchins. Sometimes females have territories near the males. Relations between damselfishes and other fishes are not always agonistic, as juveniles of some species of damselfish clean other fishes. Certain groups of damselfish are not territorial; midwater plankton-feeders may have shelter for retreat or spawning but do not maintain permanent territories.
Some butterflyfish and damselfish can be found hanging out among the tentacles of sea anemones like clownfish. They build up a resistance to the poison by rubbing parts of their body against the tentacles over a period of time. Occasionally they eat sea anemones.
Damselfish Perception and Communication
Damselfish sense and communicate with vision, touch, sound and chemicals usually detected by smelling. They use a variety of visual, auditory, tactile and olfactory cues to communicate in different situations. [Source: Monica Weinheimer, Animal Diversity Web (ADW) /=]
According to Animal Diversity Web: During courtship damselfishes respond to the sight of spawning colors and ritualized movements performed by a potential mate. Such movements may also signal the location of territory to other males or encourage reproductive synchrony. In addition to visual cues, male damselfishes use sound to ward off other males and sometimes as part of courtship and spawning rituals. They may touch and nip females to guide them toward a nest. Chemical cues from some damselfishes may encourage conspecific (individuals of the same species) juveniles to establish nearby territories and may discourage other groups of damselfish from settling.
Some damselfishes are quite good at identifying other species. The Beau Gregory damselfish is apparently able to distinguish 50 different reef fish species that occur within its territory. A second way fishes communicate visually is through dynamic display, which involves color change and rapid, often highly stereotyped movements of the body, fins, operculae, and mouth. Such displays are often associated with changes in behavioral state, such as aggressive interactions, breeding interactions, pursuit and defense.
Blue-Green Damselfish Get Stressed Out If Separated from 'Shoal-Mates'
Only a few species of damselfish shoal (school) but some of those that do form 1,000-strong groups and get stressed and lose weight if they get separated from their mates, an Australian study published in 2016 revealed. AFP reported: Scientists from James Cook University in Queensland state monitored blue-green damselfish from the Great Barrier Reef, isolating some, while allowing others to remain in their shoals to better understand why they prefer to socialise. [Source: AFP, September 22, 2016
Lauren Nadler, lead author of the study published in the Journal of Experimental Biology, said the isolated damselfish lost weight and had a higher metabolic rate, which is an indicator of stress. "We have suspected that shoaling fish gain a 'calming effect' from living in a group. But up until now we have been unable to measure how widely spread this effect is in individual fish," she said. "The fish that were isolated lost weight after the first week, which meant they were less healthy than those in groups. "Fish were calmer and less stressed when they had their shoal-mates around, with a 26 percent decrease in metabolic rate compared to individuals tested alone." She said the results showed "how important group living is for healthy fish populations".
Fellow researcher Mark McCormick said separation, which can occur during wild weather which impacts currents, put them at greater risk from predators. Parts of the Barrier Reef were hit by powerful Cyclone Nathan in 2015 year with researchers noticing a lot of blue-green damselfish living by themselves. "If these fish were out in the ocean by themselves, in order to stay alive they would need more food to keep up their energy. Since they don't have their buddies around to help look out for looming predators, foraging for food would be riskier," McCormick said. "The extra energy fish gain from shoaling is so important because it allows them to survive and reproduce and to pass on their genes to the next generation of fish." Researchers hope to conduct more studies to see what the longer-term impacts of separation are among damselfish and other species.
Damselfish Feeding, Development and Predators
Depending on species, most damselfish fall into two categories when it comes to feeding — those that eat primarily plankton such as caridea and copepods and those that eat primarily algae, with the plankton eaters typically having brighter colours and the algae feeders being duller shades of orange and brown. Bottom-dwelling damselfishes feed, for the most part, on algae and small invertebrates. They may tend “gardens” of filamentous algae. Damselfishes that live in the water column tend to feed on plankton and zooplankton. One species of damselfish, Cheiloprion labiatus, or largelipped puller, eats the polyps of live coral.
The domino damselfish (D. albisella) spends more than 85 percent of its daytime hours foraging. Larger individuals typically forage higher in a water column than do smaller ones. Males have relatively smaller stomach sizes during spawning season compared to females due to the allocation of resources for courtship and the guarding of nests. When current speeds are low, the damselfish forages higher in a water column where the flux of plankton is greater and they have a larger food source. As current speeds increase, it forages closer to the bottom of the column. Feeding rates tend to be higher when currents are faster. Smaller fishes forage closer to their substrates than do larger ones, possibly in response to predation pressures. [Source: Wikipedia +]
Longfin damselfish (Stegastes diencaeus) around Carrie Bow Cay, Belize actively protect planktonic mysids (Mysidium integrum) in their reef farms. The mysids (small shrimp-like crustaceans) fertilize the algae grown in the reef farms with their excretion and the damselfish feed on algae in the farm. Damselfish aggressively defend In the reef farms that house mysids against other fish that might feed on the mysids. The damselfish eat prey similar to the mysids small invertebrates and there is evidence that the fish and mysid have a pet-like relationship. +
Reef damselfishes protect themselves from predators by hiding in coral shelters. Free-swimming damselfishes find safety by schooling. Each group’s method of protecting itself applies to its eggs as well, except for midwater damselfishes, which must establish temporary shelter for spawning and egg laying.
Damselfish larvae hatch from a clutch of 50 to 2500 eggs, depending on the species. For some the planktonic stage may last only a day while others drift in the open ocean for a few weeks. Juveniles settle in reef areas and their coloration can be quite different from that of adults of the same species. In anemonefishes (Amphiprion and Premnas) one sexually active pair is dominant over a group of juveniles. The young grow slowly in this situation and do not reach sexual maturity until they can replace one of the dominant fish. (Allen, 1998; Hoese and Moore, 1998; Thresher, 1984) /=\
Damselfish Mating, Reproduction and Offspring
Damselfish engage in seasonal breeding and year-round breeding. They are oviparous, meaning that young are hatched from eggs. Reproduction is external, meaning the male’s sperm fertilizes the female’s egg outside her body. Damselfish can be monogamous (having one mate at a time), polyandrous (with females mating with several males during one breeding season) polygynous (males having more than one female as a mate at one time) and polygynandrous (promiscuous), with both males and females having multiple partners. /=\
According to Animal Diversity Web: The majority of damselfishes engage in a range of ritualized behavior to attract mates and prepare nest sites. The male, and sometimes the female, begin to groom and tend a rocky surface several days before spawning. He removes invertebrates and algae with his mouth, sometimes allowing certain elements to remain, as is the case with Hypsypops rubicundus, a species that weeds out all but red algae from the site. Courtship activities accompany cultivation of the potential nest. Males may give auditory signals; depending on the stage of courtship, species of Eupomacentrus emit three different types of chirps and grunts. They may also display visual signals, with most damselfish males assuming distinct colors for courtship, and many executing various movements to entice the female to the nest site. Such movements have been described as “leading,” which may include quick bursts of swimming and intermittent hovering in front of the female, “signal-jumping,” or rapid up and down movements, and “dipping,” which is similar to signal-jumping and includes an abrupt descent.
Many damselfish groups increase spawning activity in early summer. In the subtropics spawning is usually limited to the warmer months of the year, but a few spawn in fall or winter. It is common for reef-dwelling damselfishes to spawn in accordance with lunar rhythms, with greatest activity occurring near the full and new moons. Spawning usually takes place in the morning. Hypotheses suggest that lunar spawning occurs because of the increased light for nest tending, the greater currents for larvae dispersal, and the relative abundance of spawning invertebrates as a food source.
Synchronous spawning has been observed, and in some species, the higher the number of individuals in a group, the higher the degree of synchrony. Some damselfishes spawn within their permanent territory, while others (planktivorous damselfishes that live in the water column) must seek temporary territories for courtship and spawning. Location of a spawning site may involve solitary males or may be a communal activity in which schools of males, juveniles, and females travel until the males form a colony of territories on an acceptable site. Site choice varies according to species and may include rock ledges, cleaned coral branches, algal turf, empty shells, or the roofs of caves. Males typically prepare the site for spawning and then attract gravid (egg-bearing) females to the nest. The male guards the nest from predators and other males while the female lays her eggs in long rows, forming a solid, uniform mass of eggs in a single layer. The eggs are demersal (adhere to the substrate), and clutch size varies from 200 to 2500 eggs depending on the species.
Polygyny is common: one male may guard the eggs of several females, and damselfish harems have also been observed. Parental care is provided by both females and males. Male damselfishes (and in very few cases, females) guard their eggs until they hatch. They remove detritus, sand, and fungus-afflicted eggs, fan the eggs, and guard against predators. Most become more aggressive when egg-tending. In general fry are left to care for themselves after hatching, but in one Indo-Pacific species, Acanthochromis polyacanthus, parents guard their school of young near the spawning cave for three to six weeks.
Male Garibaldi damselfish tend fertilized eggs and seek mates by swimming in loops and grunting loudly and producing a thick mat of algae for the female. . Those that clean off rocks so only maroon algae grows usually easily find a mate. Studies indicate that females are more attracted by the algae than the male. The mat of algae may allude to the male’s skill at taking care of the eggs.
Global Warming, Filial Cannibalism and Damselfish
The male cortez damselfish, S. rectifraenum, is known to engage in filial cannibalism. Studies have shown it typically consumes over 25 percent of its clutches. The males generally consume clutches that are smaller than average in size, as well as those that are still in the early stages of development. Female cortez damselfish tend to deposit their eggs with males who are already caring for early-stage eggs, rather than males with late-stage eggs. This preference is seen particularly in females that deposit smaller-sized clutches, which are more vulnerable to being consumed. For the males, filial cannibalism is an adaptive response to clutches that do not provide enough benefits to warrant the costs of parental care. [Source: Wikipedia]
Philip Munday from James Cook University has shown that levels of carbon dioxide within what’s predicted for the end of the 21st century, can cause Ward’s damselfish to swim towards predators. Munday caught wild larvae and put them through a test.in water with carbon dioxide at 390 ppm (today’s level) or 550, 700 and 850 ppm (predicted levels in the future). He placed the babies in a straight arm of a Y-shaped tube, with the smell of a predator (a rock cod) wafting down one arm, and the smell of fresh danger-free water coming down the other. [Source: Ed Yong, National Geographic, July 7, 2010]
They fish behaved normally until they were kept in water with 700 ppm of carbon dioxide when half of the fish became attracted to predator smells, or 850 ppm when almost all of them became confused. This confusion proved to be a fatal one. After four days of testing, Munday placed the larvae back into natural enclosed reefs. Compared to fish that were kept in normal water, those that spent time in the CO2-swamped surroundings were bolder, more active and strayed further away from the reef. And they paid the price for their risky business. Within 30 hours, larvae that were kept in 700 ppm were 5 times more likely to be killed by predators and those kept in 850 ppm were 9 times more likely.
Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated March 2023