Damselfishes (Family Pomacentridae) make up one of the most abundant and widely-studied families of tropical reef fishes. Small and brightly colored, they are popular aquarium fish. The family Pomacentridae 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 anemonefishes (genera Amphiprion and Premnas) that live commensally with anemone hosts. Damselfishes are largely herbivorous, sometimes tending “gardens” of filamentous algae, but may eat tiny invertebrates, or in the case of anemonefishes, anemones and other organisms living symbiotically with anemones. Damselfishes manifest a range of reproductive behaviors, with groups that are polygynous, promiscuous, polyandrous, and monogamous. Anemonefishes are able to change from male to female under certain conditions
Damselfishes and anemonefishes (Amphiprion and Premnas), range from five to 36 centimeters, but most taxa are less than 25 centimeters long. Their bodies tend to be high, oval and laterally compressed, with the lateral line interrupted. Pomacentrids, 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. Coloration of adult damselfishes ranges from brilliant to drab and can vary with mood and time of day. Juveniles, especially in the territorial bottom-dwellers, often possess different, brighter colors than adults of the same species.
In most pomacentrid groups males and females differ (sexual dimorphism) externally only in the form of the urogenital papilla, and (except for one species) lack permanent sexual dichromatism. The majority, however, do 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. Adult males tend to be larger than adult females, but the opposite is true for anemonefishes (Amphiprion and Premnas), which are protandrous hermaphrodites: a male can change sex if the dominant female (the largest fish in the group) dies. In these fishes a single individual possesses ovarian as well as testicular tissue.
Pomacentrids are found throughout the world in tropical and warm temperate waters, with the majority of species occurring in the Indo-west and central Pacific region.
Damselishes and anemonefishes primarily inhabit tropical reef habitats. 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 school in the water column, some live on rocky areas or sea-grass beds, and fishes of the subfamily Amphiprionina (anemonefishes) always dwell in association with sea anemones (Actiniaria). A few deep-water species occur at the edge of the shelf at depths below 100 meters, but most damselfishes occupy shallow water between two and 15 meters deep.
Bottom-dwelling damselfishes feed, for the most part, on algae and small invertebrates. They may tend “gardens” of filamentous algae, or in the case of anemonefishes, feed on the anemone itself or other organisms that are commensal with the anemone. One species of damselfish, the Big-lip damsel (Cheiloprion labiatus), eats the polyps of live coral. Damselfishes that live in the water column tend to feed on plankton and zooplankton.
Most damselfishes, 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. 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, and anemones provide a built-in defense for areas occupied by anemonefishes. Anemonefishes, however, may compete for position in the mating dominance hierarchy, and have been observed striking each other with the pectoral fins. In the anemonefish genus Amphiprion each group contains a male/female pair whose behavioral dominance suppresses the sexual maturation of the smaller males. If one of the dominant fishes dies, the next fish in the hierarchy takes its place.
Anemonefishes, have a highly evolved relationship with sea anemones. They remain undisturbed by contact with anemone tentacles that would be fatal to other small fish. A mucous secretion is thought to protect them from the stinging nematocysts. While anemonefishes receive protection living in close proximity with their hosts, the anemones benefit as well. The fish clean the anemone’s upper surface, remove parasites, drop food on the anemone, and chase away butterflyfishes that eat anemones. Waste excretions from the fish may also help symbiotic algae within the anemone to grow. Anemonefishes spend their entire adult lives with a single host.
Damselfishes use a variety of visual, olfactory, tactile, and auditory cues to communicate in different situations. 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. Anemonefishes appear to use perception of individual color differences to recognize their monogamous partner. 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. Young anemonefishes use visual and chemical cues when choosing a preferred species of anemone as host.
Reef damselfishes gain protection from predators by hiding in coral shelters, anemonefishes by living in close contact with a host anemone, and the free-swimming damselfishes 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.
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 the Garibaldi damselfish (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.
Anemonefishes enter into permanent monogamous pairings and as a rule display a simplified pattern of courtship. Anemonefishes are protandrous, a mating system in which male individuals can become female. Ambosexual (neither sperm- nor egg-producing tissues are active) juveniles live on an anemone with a sexually mature male and female pair. If the female dies, her male partner develops into a female to take her place. The largest juvenile grows rapidly and replaces him as the dominant male.
Damselfishes appear to spawn year-round, with many groups increasing 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. 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. Some damselfish are promiscuous, and still others are monogamous. Polyandry has been reported only in an anemonefish, although monogamy is the general rule for anemonefishes. These fish stay paired for at least a year and sometimes for their entire lifetime. They spawn year-round, usually near the full moon. 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. Anemonefish most frequently live in single pairs, along with a group of sexually immature individuals, in association with an anemone. Groups containing several males and females may occasionally occur if the fish population density is extremely high. Spawning occurs at the base of the anemone, on a rock surface, or, if the anemone lives on sand, on a surface the fish drag near the anemone. The male clears the nest site by biting at the tentacles of the anemone until they withdraw, and then leads the female there for spawning, during which both fish quiver and bite the nest surface.
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, but this is not the case with anemonefishes. 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.
Three pomacentrid species, Chromis sanctaehelenae, Stegastes sanctaehelenae, and Stegastes sanctipauli, are listed as vulnerable. (The World Conservation Union, 2002)
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