Wrasses: Characteristics, Behavior and Reproduction

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WRASSES

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Wrasses (the family Labridae), are a large family of small fish with over 600 species that are often brightly colored. They are the most numerous and conspicuous fishes at tropical reefs around the world. Wrasses also comprise a significant portion of the coldwater fish population in temperate reefs. [Source: R. Jamil Jonna, Animal Diversity Web (ADW) /=]

Wrasses are second largest family of marine fishes and the third largest family in the Perciformes order. They come in a diverse range of colors, shapes, and sizes, often varying considerably within individual species. They also feed on a wide variety of prey, including other fish, zooplankton, molluscs, plant plankton and polychaetes,. They are weel known for feeding on crabs and coral. Many wrasses live in harem-based social structures and are hermaphrodites that typically change from females into males.

The fossil history of Labridae dates back to the Lower Tertiary Period and Paleocene Period (66 million to 56 million years ago). Information on their lifespan is limited but reef species are believed to live between three and five years.

Humans utilize wrasses for food, research and education and in the pet trade. Species from the Coris genera are popular aquarium fishes and two species from the Atlantic coast of North America, the cunner and the tautog, are valued as commercial and sport fish. Some medium to large wrasses are popular food fishes as well. Four labrid species are listed as vulnerable: Cheilinus undulates, Lachnolaimus maximus, Thalassoma ascensionis, and Xyrichtys virens (The World Conservation Union, 2002) /=\

Related Articles: Wrasse Species: Cleaners, Clowns and Amazing Jaws ioa.factsanddetails.com ; Humphead Wrasse: Amazing Reef Fish and High-price Delicacy ioa.factsanddetails.com ; CORAL REEFS ioa.factsanddetails.com ; CORAL REEF LIFE ioa.factsanddetails.com REEF FISH ioa.factsanddetails.com

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

Wrasse Habitat and Where They Are Found

Birdmouth wrasse
Wrasses occupy all tropical seas and range quite far into temperate waters, reaching as far north as Norway. Many temperate species in the genera Oxyjulius, Tautoga, Tautogolabrus, Semicossyphus, and Labrus can be found in both the Atlantic and Pacific Oceans. Wrasses are most highly concentrated off the coasts of Australia where about 165 species and 42 genera are represented.[Source: R. Jamil Jonna, Animal Diversity Web (ADW) /=]

Wrasses can be found in a wide variety of habitats: rocky or coral reefs, tidal pools, grass beds, and open sand bottoms. Many species prefer specific environments. Hemipteronotus, for example, like mixed turtle grass and sandy patch areas; Doratonotus prefer turtle grass beds,, and hogfishes favor weed-covered rocky flats. Plankton feeders, such as Clepticus, often concentrate in large schools at reef fronts, reef gaps, or other areas where plankton is concentrated. At the same time, some species, such as the slippery dick, can be found in a wide range of habitats. Some are found brackish water estuaries and intertidal areas.

Wrasses occupy a wide range of water temperatures and incubation time is directly affected by water temperature. In laboratory experiments incubation took approximately 24 hours at 27̊C (81̊F). The planktonic stage is estimated to be around one month, although very little is known about this stage. The age or size at which individuals reach sexual maturity depends on the maximum size of the species.

Wrasse Physical Characteristics

Wraases are cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature), bilateral have symmetry (both sides of the animal are the same) and are polymorphic (“many forms”, species in which individuals can be divided into easily recognized groups, based on structure, color, or other similar characteristics). Sexual Dimorphism (differences between males and females) is present in some speceis: Males are larger than females. Sexes are colored or patterned differently with the male being more colorful. Males and females have different shapes.[Source: R. Jamil Jonna, Animal Diversity Web (ADW) /=]

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Most wrasses are quite small, usually below 20 centimeters (8 inches). The smallest species, Minilabrus striatus of the Red Sea, reaches a maximum length of only 4.5 centimeters (1.8 inches). According to Animal Diversity Web: The genera Pseudocheilinus and Doratonotus contain several other dwarf wrasses. One species, Conniella apterygia, is so small that it lacks even pelvic fins and a supporting skeleton. The largest wrasse, Cheilinus undulatus, can reach a length of about 2.3 meters (7.5 feet) and weighs more than 150 kilograms (330 pounds)

Wrasses characteristically have a protruding mouth, cycloid scales, and a single continuous dorsal fin lacking an obvious notch between the soft and spiny portions. The lateral line may be continuous or interrupted.. Wrasses are most easily identified by their pointed snouts and prominent canine teeth in the front of the jaws, which often project forward. Wrasses mouths often have separate jaw teeth that jut outwards. Many species can be recognized by their thick lips, the inside of which are sometimes curiously folded, a peculiarity which gave rise to the German name of "lip-fishes" (Lippfische) and the Dutch name of lipvissen. The dorsal fin has eight to 21 spines and six to 21 soft rays, usually running most of the length of the back.

Often, there is considerable diversity of colors and shapes within individual species. Some wrasses progress through “phases”, with each phase accompanied by a change in morphology (shape and color). Dominant males (and sometimes females) are the most distinctly colored, with complex patterns of red, yellow, green, blue and black. Subordinate males and females are smaller than dominant individuals and are often drab-colored with cryptic patterns. Juveniles range in coloration from bright yellow and orange to drab gray and brown, and some have camouflaging patterns. /=\

Wrasse Behavior, Communication and Perception

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Wrasses are diurnal (active during the day), motile (move around as opposed to being stationary), territorial (defend an area within the home range), social (associate 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). They can be parasitic (living in or on another animal. Studies show that some wrasse species are capable of tool use, using rocks to smash open sea urchins.[Source: R. Jamil Jonna, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web (ADW): A characteristic feature of wrasses is their form of propulsion, which relies almost entirely on the pectoral fins. In what is termed “pectoral fins only” propulsion or labriform locomotion, the fish bounces through the water column using the pectoral fins and the caudal fin (tail) is only used when a burst of speed is needed. Wrasses are also strongly diurnal (active during the daytime), (only active during the daytime) and, like parrotfishes, many bury themselves in the sand or seek crevices to hide in at night. Interestingly, observations of wrasses in captivity seem to suggest a rapid eye movement (REM) stage while sleeping. REM sleep is usually associated with dreaming in “higher” vertebrates. Wrasses may forage individually, in pairs, or in large schools depending on the species.

Wrasses communicate with vision and use mimicry. They sense using vision, touch and chemicals usually detected with smell. Most wrasses rely on vision to find their prey. Visual recognition may also be important for terminal phase (TP) males to identify harem members. Although TP males are susceptible to streaking attempts by initial phase (IP) males, no IP males have been found in harem-forming species. This suggests that IP males are unable to mimic IP females, despite very similar morphology.

Wrasse Food, Eating Behavior and Predators

Wrasses are primarily carnivores, Some are molluscivores (mainly eat mollusks), herbivores (primarily eat plants or plants parts) and omnivores (eats a variety of things, including plants and animals). Many wrasses are specialized feeders, which reflected by the highly variable skull and body shape, modified pharyngeal jaw, and prominent canines. [Source: R. Jamil Jonna, Animal Diversity Web (ADW) /=]

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Wrasses eat a wide variety of food: fish, ectoparasites, mollusks, polychaete worms, decapod crabs, corals, coral mucous, amphipods, various echinoderms, plankton, and several types of vegetation. Many small wrasses follow larger fishes and exploit any reef bottom disturbances that help to reveal well-camouflaged animals. Plankton feeders often form schools in reef gaps, reef fronts or other areas with current. The food habits of cleaner wrasses are probably most well known. Cleaner wrasses remove mucous, parasites and scales from the bodies of larger fishes. Finally, some piscivorous (fish-eating) wrasses mimic harmless fishes to attract prey.

Their main known predators are larger fih. Many juvenile wrasses are colored to avoid predation and some find protection among the tentacles of sea anemones. Nearly all adult wrasses bury themselves in sand at night to avoid predators. A few species seek out reef crevices and produce a foul-smelling mucous bag to deter predators while sleeping. Razorfishes (Hemipteronotus, Xyrichtys) also use the sand for protection during the day by diving into the bottom. Razorfishes are apparently quite agile in this environment, sometimes resurfacing several meters from where they entered.

According to Animal Diversity Web: The relationship between wrasse species and their invertebrate prey is a spectacular example of coevolution. As invertebrates have developed anti-predator adaptations, such as spines, toxins, heavy armor, and adherence to the substrate, wrasses have evolved simultaneously. Some physical changes include the development of strong, hard beaks and a second set of strong teeth in the throat (pharyngeal jaw), making it possible to crush hard-shelled invertebrates. A conspicuous behavioral adaptation is “following behavior.” As larger fish disturb the substrate, some wrasses follow close behind to capture exposed invertebrates. Other small wrasses have become adept at combing the reef for invertebrates too small for most fishes to prey upon. Finally, some wrasses use their snouts to flip rocks and pieces of coral to expose hidden invertebrates.

Wrass Sexuality and Changing from Females to Males

Wrasses are sexually dimorphic. Many species are capable of changing sex. Juveniles are a mix of males and females (known as initial-phase individuals), but the largest adults become territory-holding (terminal-phase) males.

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Wrasses often start out as females and become males who vigorously defend territories. As small females grow they become large enough to defend their own territories. When the become big enough they change sex, fight off male rivals and mate with females who come to visit.

If a male leaves the group, a female changes her behavior in minutes. Her color changes in a day. Within a week she produces sperm instead of eggs. The dominant female controls sexual activity in her group. If she leaves and doesn't return her mate becomes the dominant female and a younger male become her mate.

Wrasses are very good at changing color. One species quickly changes from ripples of green on an orange background to mostly orange when it suddenly opens it mouth to warn off a rival or stall a predator. Male flasher wrasses flare out fins with bright blue markings that flash on and off.

Wrasse Reproduction

Wrasses are protogynous (hermaphrodites that have female organs and eggs before male organs and sperm) and are sequential hermaphrodites in which individuals change their sex at some point in their lives and typically produces eggs and sperm at different stages their lives. Reproduction is external, meaning the male’s sperm fertilizes the female’s egg outside her body. [Source: R. Jamil Jonna, Animal Diversity Web (ADW) /=]

Wrasses are oviparous (young are hatched from eggs) and iteroparous (offspring are produced in groups). They engage in year-round breeding and parental care is provided by males. Some temperate wrasse species, such as the ballan wrasse and Anampses cuvieri, are demersal nest builders. The nests are usually made out of plant material and the male guards the eggs after they are deposited.

According to Animal Diversity Web: Like parrotfishes, many wrasses utilize some of the most complex and unusual reproduction systems known to fishes. Males can be either primary (born male), or secondary (females that have undergone sex change). In some species there are no secondary males while in others all individuals are born female (monandric) and change sex when necessary. In the most complex systems, species are diandric — both primary and secondary males exist in the population. In these species, individuals proceed through three distinct phases, marked by color differences. In fact, the color differences are so pronounced that for over 200 years researchers regarded some phases as distinct species. Sexually immature juveniles represent the first phase.

The second, known as the initial, phase (IP) can include sexually mature males or females, which are impossible to tell apart without internal examination or observation during spawning. IP males and females may group spawn in some species. The terminal phase (TP) includes only mature males, which display brilliant colors. TP males usually dominate reproductive activity through a harem-based social system. The death of a TP male serves as a social cue for an IP female to change sex and behavior. The morphology of IP males may also change in response to the death of a TP male. In some cases, IP males attempt to fertilize IP females by following a TP male and IP female pair during spawning. In this behavior, called “streaking,” IP males follow the pairs at peak spawning and release a large cloud of gametes in an attempt to overwhelm fertilization by the TP male. This is thought to increase the fecundity (ability to produce offspring) of IP males. IP males are well equipped to perform streaking as they have larger gonads and so are able to produce more gametes, while TP males have smaller testes and rely on aggression to deter other males. The larger volume of milt (gametes) produced by IP males is related to group spawning events with IP females, in which competition for fertilization is intense and more milt is needed. /=\

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Wrasse Mating and Spawning

Wrasses are polygynous (males having more than one female as a mate at one time) and polygynandrous (promiscuous), with both males and females having multiple partners. Describing the mating of flasher wrasses, Les Kaufman wrote in National Geographic: “Males shoot neon blue stripes across their bodies and outstretched fins, creating miniature laser-light show. Spurred to passion by a male’s display of lights, a female rose in the water column with her chosen suitor and released an explosive burst of eggs to mix with his sperm. Job done, the male instantly went drab, and the consummated pair sped to get safety of the reef.”

According to Animal Diversity Web: Some specific examples of wrasse mating systems demonstrate the complexity and variation of the phase system described above. For instance, the cleaner wrasse, which is monandric (all individuals are born female), forms harems that are held together by male aggression towards subordinate females. With the death of the dominant male, subordinate females jockey for position and the newly dominant female adopts aggressive male behavior within a few hours. Each individual moves a step up in the dominance hierarchy and the last position is filled by a juvenile. If the newly dominant female is able to withstand attempts by neighboring males to take over the vacant harem, she will become a fully functional male within a two to four days. Some other harem-forming species are Cirrhilabrus temminckii, Cirrhilabrus jordani, Labroides bicolor, Hemipteronotus splendens, Pseudocheilinus hexataenia and Macropharyngodon moyeri. The Caribbean species Halichoeres garnoti is also monandric, but individuals do not exhibit territorial (defend an area within the home range),ity or conspicuous dominance relationships, nor do they use aggressive actions to maintain sexual state. Instead, size or some size-related factor determines which individual will fill the male role. In Halichoeres garnoti males are larger than females and both sexes behave similarly. While these examples focus on the mating extremes of wrasses, most species fall between the systems of the cleaner wrasse and Halichoeres garnoti in terms of the influence of social control on sex reversal. Other hermaphroditic but non-harem-forming species include Halichoeres bivittatus and Halichoeres poeyi, Halichoeres maculipinna and possibly Thalassoma lunare. Finally, some species, such as Oxyjulis californica and Crenilabrus melops, do not follow the phase system at all as they are not hermaphroditic, and there are probably more non-hermaphroditic species yet to be found. [Source: R. Jamil Jonna, Animal Diversity Web (ADW) /=]

In tropical wrasses spawning occurs year-round but some temperate species seem to restrict spawning to warmer parts of the year. Spawning typically occurs along the outer edge of patch reefs or along the outer edges of more extensive reef complexes. The correlation between spawning and lunar periodicity (the lunar cycle) is sketchy in some species and non-existent in most that have been investigated. Spawning in several species corresponds with outgoing tides, however, many species spawn at a particular time in the day, regardless of tidal patterns. This variation may be due to local conditions. For instance, in areas where tidal forces are weak, factors like time of day or light intensity may have more influence. However, evidence from different species on the same reef suggests that temporal (measured time) differences in spawning evolved to decrease the probability of hybridization with other species. /=\

Wrasses may spawn in groups or pairs depending on the species or phase of individuals. Typically, group or aggregate spawning occurs between initial phase (IP) individuals, which are diandric (containing male and female IP individuals). However, in some species, such as Thalassoma cupido, Thalassoma lucasanum, and Halichoeres bivitattus, terminal phase (TP) males have been observed participating in group spawning. The size of the spawning groups ranges from a dozen to several hundred individuals.

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Males outnumber females, sometimes by as much as ten to one. Paired spawning is found in many, if not all, tropical wrasses and involves a TP male and IP female. In rare cases, IP individuals also spawn in pairs. Most species defend small territories only during spawning. Currently Anampses cuvieri is the only known species of tropical wrasse to produce demersal eggs (eggs laid on the bottom as opposed to being released in the water column). Demersal spawning of Anampses cuvieri was only observed in captivity and still needs to be confirmed, but work on other species of this genus seems to support this observation. /=\

Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA, group pictures from researchgate, EvoDevo and Oceans, Reefs and Aquariums (ORA)

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

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