| Wrasses | |
|---|---|
 | |
| Moon wrasse (Thalassoma lunare) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Labriformes |
| Suborder: | Labroidei |
| Family: | Labridae G. Cuvier, 1816 |
| Tribes | |
Thewrasses are afamily,Labridae, of marineray-finned fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 81 genera, which are divided into nine subgroups or tribes.[1][2][3]
They are typically small, most of them less than 20 cm (7.9 in) long, although the largest, thehumphead wrasse, can measure up to 2.5 m (8.2 ft). They are efficient carnivores, feeding on a wide range of smallinvertebrates. Many smaller wrasses follow the feeding trails of larger fish, picking up invertebrates disturbed by their passing.[4] Juveniles of some representatives of the generaBodianus,Epibulus,Cirrhilabrus,Oxycheilinus, andParacheilinus hide among the tentacles of the free-livingmushroom corals andHeliofungia actiniformis.[5][6]
The word "wrasse" comes from theCornish wordwragh, alenited form ofgwragh, meaning an old woman or hag, viaCornish dialectwrath. It is related to theWelshgwrach andBretongwrac'h.[7]
Parrotfish were traditionally regarded as comprising their ownfamily (Scaridae), but are now often treated as a subfamily (Scarinae) or tribe (Scarini) of the wrasses (Labridae), being nested deep within the wrasse phylogenetic tree.[8] Theodacine wrasses, traditionally classified as forming their own family, were found nested deep within the wrasse tribeHypsigenyini, and most closely related to thetuskfishes.[9]Eschmeyer's Catalog of Fishes currently places the parrotfishes within the wrasses, but treats the odacids as a distinct family.[10]
The following fossil genera are also known, lacking a proper tribal placement:[11]
Fossil wrasses date to theEarly Eocene of Monte Bolca, Italy. Among these isPhyllopharyngodon, which can uniquely be placed in the extant tribeHypsigenyini.[11] Wrasses appear to have had an even wider distribution in prehistoric times, with fossil remains being known from theMiddle Eocene-agedLa Meseta Formation of Antarctica. They were presumably wiped out from Antarctica following the continent's cooling during theOligocene.[13]
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Wrasses haveprotractile mouths, usually with separate jaw teeth that jut outwards.[14] Many species can be readily recognized by their thick lips, the inside of which is sometimes curiously folded, a peculiarity which gave rise to the German name of "lip-fishes" (Lippfische),[15] and the Dutch name oflipvissen. Thedorsal fin has eight to 21 spines and six to 21soft rays, usually running most of the length of the back. Wrasses aresexually dimorphic. Many species are capable ofchanging sex. Juveniles are a mix of males and females (known as initial-phase individuals), but the largest adults become territory-holding (terminal-phase) males.[14]
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The wrasses have become a primary study species in fish-feedingbiomechanics due to their jaw structures. The nasal andmandibular bones are connected at their posterior ends to the rigidneurocranium, and the superior and inferior articulations of themaxilla are joined to the anterior tips of these two bones, respectively, creating a loop of four rigid bones connected by moving joints. This "four-bar linkage" has the property of allowing numerous arrangements to achieve a given mechanical result (fastjaw protrusion or a forceful bite), thus decouplingmorphology from function. The actual morphology of wrasses reflects this, with many lineages displaying different jaw morphology that results in the same functional output in a similar or identical ecological niche.[14]
Most wrasses inhabit the tropical and subtropical waters of the Atlantic, Indian, and Pacific Oceans, though some species live in temperate waters: theBallan wrasse is found as far north as Norway. Wrasses are usually found in shallow-water habitats such ascoral reefs and rocky shores, where they live close to the substrate.
Most labrids areprotogynoushermaphrodites within aharemicmating system.[16][17] A good example of this reproductive behavior is seen in theCalifornia sheephead. Hermaphroditism allows for complex mating systems. Labroids exhibit three different mating systems:polygynous,lek-like, andpromiscuous.[18] Group spawning and pair spawning occur within mating systems. The type of spawning that occurs depends on male body size.[17] Labroids typically exhibitbroadcast spawning, releasing high numbers ofplanktonic eggs, which are broadcast bytidal currents; adult labroids have no interaction with offspring.[19] Wrasses of a particular subgroup of the family Labridae, Labrini, do not exhibit broadcast spawning.
Sex change in wrasses is generally female-to-male, but experimental conditions have allowed for male-to-female sex change. Placing two maleLabroides dimidiatus wrasses in the same tank results in the smaller of the two becoming female again.[20] Additionally, while the individual to change sex is generally the largest female,[21] evidence also exists of the largest female instead "choosing" to remain female in situations in which she can maximize her evolutionary fitness by refraining from changing sex.[22]
The subgroup Labrini arose from a basal split within family Labridae during theEocene period.[3] Subgroup Labrini is composed of eight genera, wherein 15 of 23 species exhibit broodcare behavior,[19] which ranges from simple to complex parental care of spawn; males build algae nests or crude cavities, ventilate eggs, and defend nests againstconspecific males and predators.[19] In species that express this behavior, eggs cannot survive without parental care.[23] Species ofSymphodus,Centrolabrus, andLabrus genera exhibit broodcare behavior.
Wrasses exhibit three types of sexual development, depending on the species. Sex in this context refers to functional sex, ie the individual's role when mating. Some species show functionalgonochorism, meaning that they are born functionally either male or female, and remain so for their entire life; there is no sex change. Meanwhile, functionally hermaphoditic species exhibit sex change, and areprotogynous, meaning that individuals that are functionally female can become functionally male. These protogynous species are either monandric (all individuals are born functionally female, but can become functionally male) or diandric (individuals can be born either female or male, and individuals that are born female can become male).[24]
Evolutionarily, wrasse lineages trend towards developing monandry.[25] Monandric lineages rarely transition directly to diandry, instead transitioning through functional gonochorism first on the pathway to diandry.[24]
Many species of wrasses have been recorded using large rocks or hard coral as "anvils", upon which they smash open hard-shelled prey items. At least some of these species can remember to use a particular rock or coral repeatedly for this purpose.[26] This behaviour usually involves invertebrate prey such as clams, sea urchins, and crabs, but on one occasion, ablue tuskfish was filmed smashing a younggreen sea turtle on an anvil.[27][26]
21 species of 8 genera have been documented exhibiting this behaviour, includingChoerodon (C. anchorago,C. cyanodus,C. graphicus,C. schoenleinii),Coris (C. aygula,C. bulbifrons,C. julis,C. sandeyeri),Cheilinus (C. fasciatus,C. lunulatus,C. trilobatus),Thalassoma (T. hardwicke,T. jansenii,T. lunare,T. lutescens,T. pavo),Symphodus (S. mediterraneus),Halichoeres (H. garnoti,H. hortulanus),Bodianus (B. pulcher), andPseudolabrus (P. luculentus).[26][28]
Cleaner wrasses are the best-known of thecleaner fish. They live in acleaning symbiosis with larger, often predatory, fish, grooming them and benefiting by consuming what they remove. "Client" fish congregate at wrasse "cleaning stations" and wait for the cleaner fish to removegnathiid parasites, the cleaners even swimming into their open mouths and gill cavities to do so.[29]
Cleaner wrasses are best known for feeding on dead tissue, scales, andectoparasites, although they are also known to 'cheat', consuming healthy tissue and mucus, which is energetically costly for the client fish to produce. Thebluestreak cleaner wrasse,Labroides dimidiatus, is one of the most common cleaners found on tropical reefs. Few cleaner wrasses have been observed being eaten by predators, possibly because parasite removal is more important for predator survival than the short-term gain of eating the cleaner.[30]
In a 2019 study, cleaner wrasses passed themirror test, the first fish to do so.[31] However, the test's inventor, American psychologistGordon G. Gallup, has said that the fish were most likely trying to scrape off a perceived parasite on another fish and that they did not demonstrate self-recognition. The authors of the study retorted that because the fish checked themselves in the mirror before and after the scraping, this meant that the fish had self-awareness and recognized that their reflections belonged to their own bodies.[32][33][34] In a 2024 study, "mirror-naive" bluestreak cleaner wrasse were reported to initially show aggression to wrasse photographs sized 10% larger or 10% smaller than themselves, regardless of size. However, upon viewing their reflections in a mirror, they avoided confronting photographs 10% larger than they were.[35]
In the Western Atlantic coastal region of North America, the most common food species for indigenous humans was thetautog, a species of wrasse.[15] Wrasses today are commonly found in both public and homeaquaria. Some species are small enough to be consideredreef safe. They may also be employed as cleaner fish to combatsea-lice infestations insalmon farms.[36] Commercial fish farming of cleaner wrasse for sea-lice pest control in commercial salmon farming has developed in Scotlandas lice busters, with apparent commercial benefit and viability.
As all fish, labrids are thehosts of a number ofparasites. A list of 338 parasite taxa from 127 labrid fish species was provided by Muñoz and Diaz in 2015.[37] An example is thenematodeHuffmanela ossicola.
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