Physical characteristics

This grouping of fishes is varied, but vibrant color is a trademark of many species in the four families, and has made wrasses and damselfishes the highlights of reef-diving excursions. In addition, the scarids, labrids, and odacids all share unusual pharyngeal modifications that serve as additional chewing surfaces to grind kelp, hard-shelled invertebrates, and other dietary items.

Generalizations can also be made about each of the four families. Most labrids, or wrasses, have gapped and outward-projecting teeth on protrusible upper and lower jaws. The dorsal fin typically has less than 15 spines; some have as many as 21 spines and 6-21 soft rays. The anal fin has 4-6 spines and 7-18 soft rays. Other than these characteristics, little else is noticeably uniform among this highly diverse family. Maximum adult size in the family ranges from about 2 in (5 cm) in a variety of species, to more than 8 ft (2.5 m) in the hump-head wrasse (Cheilinus undulatus).

A brindlebass (Epinephelus lanceoletus) having its teeth cleaned by a bluestreak cleaner wrasse (Labroides dimidiatus). (Photo by Mark Smith/Photo Researchers, Inc. Reproduced by permission.)

The pomacentrids, or damselfishes, are characterized by a deep, compressed body; a small mouth with short canine teeth; a usually two-spined anal fin; one dorsal fin with spines numbering 8-17, and 10-18 rays; and a lack of teeth on the palate. Maximum adult size ranges from 1.6 in (4 cm) in some Chromis and Chrysiptera species, to over 12 in (30 cm) in the garibaldi (Hypsypops rubicundus) and giant damselfish (Mi-crospathodon dorsalis).

Scarids, or parrotfishes, have a rather distinctive "parrot's beak" resulting from a fusion of the teeth and often fleshy lips. The dorsal fin has 9 spines and 10 soft rays, the anal fin has 3 spines and 9 soft rays, and the pectoral fin has one spine and 5 soft rays. Large scales are evident even from some distance.

The small Odacidae family is still quite diverse, and is occasionally described as being intermediate between the scarids and labrids. The jaw teeth are fused in a manner similar to the parrotfishes, but they have a different dorsal fin pattern, with 12-23 spines, compared to the 9 spines in scarids. Odacids, the rock whitings or butterfishes, have the more elongate body seen in many labrids, but do not have the pro-trusible jaws.

Distribution

Parrotfishes, wrasses, and damselfishes occupy mainly tropical, marine waters of the Atlantic, Pacific, and Indian Oceans, but some species, particularly wrasses, extend well into cooler waters, and a few damselfishes exist in estuaries and occasionally venture into fresh water. The rock whitings are found in the temperate, coastal waters of Australia and New Zealand.

Habitat

This group comprises primarily reef-associated fishes, although a few make their homes in the open sea. The reefs

A threespot damselfish (Stegastes planifrons) in its nest amidst fire coral near Bonaire, Netherlands Antilles. (Photo by Charles V. Angelo/ Photo Researchers, Inc. Reproduced by permission.)
Mated pair of spine-cheek anemonefish moves among the tentacles of its host, the bubble tip anemone. (Illustration by Joseph E. Trumpey)

provide a source of refuge, as many of the species use the nooks and crannies in the coral as daytime hiding places from predators. A number of species also gain nourishment directly from the coral by nipping off polyps and grinding them with their pharyngeal jaws. Some species, particularly the juveniles, prefer the shallower, protected waters of lagoons and bays, and the adults of many reside in waters of steep, outer, reef slopes.

A number of parrotfishes live among beds of sea grass or in rocky reefs, and wrasses frequently require living coral reefs, but some do very well among dead coral. Damselfishes generally live in rocky and coral reefs, but individual species may prefer open water as deep as 300 ft (91 m) or more, or shallow habitats of as little as 12 ft (3.7 m) in either the open sea or in sheltered areas with calmer waters. Some species within these four families prefer very specific habitats. Anemonefishes (genera Amphiprion and Premnis), for example, may require the presence of a particular species of anemone.

Behavior

Two of the most well-known behaviors of this group of fishes involve that of certain damselfishes and their symbiotic relationship with large sea anemones, and that of parrotfishes, which produce a mucus "cocoon" that surrounds them while they sleep at night.

Known as anemonefishes, or clownfishes, the 30 damselfishes in the genera Amphiprion and Premnas move among and between the dangerous tentacles of the sea anemone, even sleeping within them. Stinging cells (nematocysts) on the surface of the tentacles normally sting and paralyze prey fish for easy consumption by the anemone. The anemonefishes, however, live peacefully among the anemones. Current consensus is that a protective mucus coat on the anemonefish shields it from the sting of the tentacle. The relationship is symbiotic because both species gain from it. The anemonefish receives shelter from predators, while helping to maintain the health of the anemone by picking off organisms and detritus from its tentacles. The relationship is more important to the anemone-fishes than to the anemones, because the fishes are unable to escape predation without the sanctuary of the anemone, but anemones can and do survive in the absence of the fishes.

Parrotfishes, on the other hand, have their own presumably protective behavior. At night, these diurnal animals prepare for sleep by generating a tube of mostly clear mucus that surrounds the body. The tube forms in about 30-60 minutes. There is some debate over whether cocoon formation is a behavioral trait or simply the result of normal mucus secretions that accumulate because the fish is stationary. Either way, the mucus tube appears to provide the fishes with some protection from predators by masking them, and perhaps by surrounding them with an unpleasant-tasting barrier.

Feeding ecology and diet

Herbivores and carnivores exist within this group, with the diet of many species comprising both plants and animals.

A slingjaw wrasse (Epibulus insidiator) sucks up prey, a humbug damsel (Dascyllus aruanus), through its long jaws. (Illustration by Marguette Dongvillo)

A parrotfish sleeps in a mucous cocoon in the reefs of Fiji. (Photo by Stuart Westmorland/CORBIS. Reproduced by permission.)

Feeding habits vary. The odacids are mainly herbivores, with a few dining on kelp, a coarse seaweed shunned by most other species. One study of the butterfish Odax pullus showed that this herbivorous odacid has an active symbiotic relationship with gut microbes that assists in the digestion of the plant matter. Several damselfishes hold feeding territories and even cultivate algal beds. Many scarids and odacids are herbivorous grazers, using their parrotlike beaks to scrape algae from rocks and coral, or to crush open a hard-shelled invertebrate, such as a mussel or sea urchin. A few even eat coral polyps. Some parrotfishes are so aggressive in their feeding habits that they are considered a cause of reef erosion, as they not only alter the reef, but also excrete a great deal of silty sediment that coats the reef structure. As a rule, species that dine on coral, mollusks, and other crunchy prey have more rounded teeth attuned to grinding. The teeth of species that favor softer dietary items are more pointed.

The wrasses are primarily carnivores, and generally choose from a variety of hard-shelled, invertebrate prey. Some, however, prefer that their food come to them, and take their diet of plankton from the water column. One of the most unusual feeding behaviors in this group is seen in the cleaner wrasses.

A cleaner wrasse cleans a fish (left inset). A cleaner mimic is a blenny that mimics the cleaner wrasse, but instead of cleaning the larger fish, it rips out a gill filament to eat (right inset). (Illustration by Brian Cressman)

This group of small fishes in the genus Labroides have specific sites where they provide cleaning services to other fishes. Fishes come to these so-called cleaning stations, and announce their desire to be cleaned by exhibiting stereotyped behaviors through movements of their mouths or bodies. The cleaner wrasses strike a deal by responding with their own behaviors, including brushing the "client" with their fins, and the cleaning begins. The wrasses pick over the body, fins, and head of the client fish, and may even enter the gill chamber and mouth to remove crustacean ectoparasites, mucus, dead skin, dislodged scales, and other detritus. Both client and wrasse benefit from the arrangement: the cleaner is fed, and the client is cleaned.

Other wrasses also provide cleaning services, particularly juveniles of the genus Thalassoma. A study of Noronha wrasse (T. noronhanum) and a client fish, the piscivorous coney (Cephalopholis fulva) indicated that client fishes sometimes take advantage of the situation and eat the cleaner. In this study, scientists observed predation in two instances, both of which occurred when the wrasse was tending the coney away from its normal cleaning station.

Fishes in these four families may fall prey to larger bony fishes. The primary predators include larger serranids, syn-odontids, aulostomids, and members of other families.

Reproductive biology

Perhaps most notable characteristics of this group of fishes are the three separate color phases and sex reversal associated with many species. The typical three-phase lifestyle begins with a juvenile (immature) phase, then an adult initial phase, and finally the terminal phase. Each has a distinctive appearance that differs from species to species. In the bluehead wrasse (Thalassoma bifasciatum), for example, juveniles are bright yellow, initial-phase adults are yellow with black stripes, and terminal-phase males are deep blue with a green rear and midbody, and bold, black and white bands behind the head. The initial-phase adults in many species are almost all females, and in most cases, the few initial-phase males look the same as their female counterparts. The initial and terminal phases are usually so different that inexperienced divers

frequently assume they are two species. This three-phase lifestyle is characteristic of the wrasses and parrotfishes. Dam-selfishes typically shift gradually from a colorful juvenile pattern into a the more drab suit of an adult.

Along with the three color phases in the parrotfishes and wrasses, these two families engage in sex reversal. Here, the initial-phase adults usually are mostly female, often living in a small grouping, or harem. Each harem has one terminal-phase male, which mates with the adult females. The females form a hierarchy within the harem, with one dominant female followed by a second-ranking female, a third, and so on. If the male is removed from the group through predation or other means, the dominant female steps up to become, socially and physiologically, the terminal-phase male. The social change can occur in as little as a few hours. The physiological change, including the development of functional testes, may take a couple of weeks. The hierarchy among the females continues, with the second-ranking female moving into the position of dominant female, and the rest moving up a step in the hierarchy.

Initial-phase males are also capable of becoming the terminal-phase male, and this frequently occurs in non-haremic groups. In this reproductive arrangement, the terminal-phase males set up a territory where females may enter for one-on-one mating. When the terminal-phase male is removed, an initial-phase male or female may take his place.

Another reproductive strategy is available for initial-phase males, which are sexually mature. Initial-phase males will form schools, and chase individual females as they make their way to a terminal male's territory, and "sneak-spawn" with them. Although sole paternity is out of the question for individual sneak-spawners, at least the initial-phase male can add his milt to the mix and perhaps fertilize a few eggs. Many of these fishes also engage in mass spawning, in which both terminalphase and initial-phase males participate.

Damselfishes may not have the obvious phase differences, but they do have interesting reproductive behavior. As a group, these fishes are quite territorial of their mating sites and will mount vicious attacks on intruders, complete with rushes, grunts, and bites. The male typically clears a nest site, engages in ritualistic visual and tactile displays to attract a female, mates, and then cares for the eggs until they hatch, when the young are on their own. In an unusual twist, the marine damselfish (Acanthochromis polyacanthus) continues its care of the young for several months after hatching. Anemonefishes are noted because they reverse gender like the parrotfishes and wrasses, but in the opposite direction. In an anemone, this species exists in small groups with one large female, one large male, and several small, immature males. Should the large female be removed, the most-dominant immature male can develop to take her place.

Little is known about reproduction in odacids overall, but the butterfish O. pullus does change sex from female to male and exists in small harems. Females lay their eggs directly into a plankton column.

Conservation status

Eight species are included on the IUCN Red List, all of them categorized as Vulnerable. The eight species are:

in the Pomacentridae, Chromis sanctaehelenae, Stegastes sanc-taehelenae, and S. sanctipauli; in the Labridae, Cheilinus un-dulatus, Lachnolaimus maximus, Thalassoma ascensionis, and Xyrichtys virens; and in the Scaridae, Scarus guacamaia.

Significance to humans

Aesthetic, particularly to divers, and often popular in the aquarium trade. A few are minor commercial food fishes.

1. Garibaldi damselfish (Hypsypops rubicundus); 2. Blue chromis (Chromis cyanea); 3. Yellowtail damselfish (Microspathodon chrysurus) intermediate stage; 4. Bluehead adult (Thalassoma bifasciatum); 5. Bluehead (Thalassoma bifasciatum) intermediate stage; 6. Clown anemonefish (Amphiprion ocellaris); 7. Humphead wrasse (Cheilinus undulatus). (Illustration by Joseph E. Trumpey)

Odax Pullus

1. California sheephead (Semicossyphus pulcher); 2. Bluestreak cleaner wrasse (Labroides dimidiatus); 3. Hogfish (Lachnolaimus maximus); 4. Striped parrotfish (Scarus iseri); 5. Butterfish (Odax pullus); 6. Juvenile stoplight parrotfish (Sparisoma viride); 7. Initial phase of the stoplight parrotfish; 8. Terminal phase of the stoplight parrotfish. (Illustration by Patricia Ferrer)

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