Bluestreak cleaner wrasse

A cleaner wrasse that eats parasites and may recognize itself.

The bluestreak cleaner wrasse (*Labroides dimidiatus*) is one of several cleaner wrasse species inhabiting coral reefs stretching from eastern Africa and the Red Sea to French Polynesia. It feeds on parasites and dead skin from larger fish in a mutualistic arrangement that gives the wrasse both food and protection while boosting the health of its clients. It is also noteworthy for possibly having passed the mirror test. Genetic studies of *L. dimidiatus* have split the species into two distinct evolutionary branches. Populations in the Indian Ocean generally have different stripe widths than those in the western Pacific. Japanese cleaner wrasses, despite looking different, fall into the same group as Indian Ocean fish, and both branches overlap near Papua New Guinea. Two closely related species, *L. pectoralis* and *L. bicolor*, sit within the *L. dimidiatus* branch, suggesting the bluestreak cleaner wrasse may actually be polyphyletic, containing several species. This wrasse averages 10 cm in length, reaching up to 14 cm. It is identified by a wide, black stripe running lengthwise along its side and through the eye, with a white (sometimes slightly yellowish) back and belly. The white turns bright blue toward the front, while the black band widens at the tail. Juveniles are black with an electric-blue line. The bluestreak cleaner wrasse lives on tropical coral reefs from the Red Sea and Indian Ocean to the western Pacific, including Papua New Guinea, Japan, Fiji, and French Polynesia. It was first recorded in the Kermadec Islands Marine Reserve north of New Zealand in 2015, after researchers reviewed hundreds of hours of unused documentary footage. Cleaner wrasses typically occupy cleaning stations, which may be run by groups of juveniles, pairs of adults, or a group of females led by a dominant male. When potential clients approach, the wrasses perform a dance-like motion, moving their rear up and down. The larger fish recognize them as cleaners by their lateral stripe and movement patterns. This greeting helps secure a feeding opportunity. In response, the client fish adopts a species-specific pose, allowing the wrasse access to its skin, gills, and sometimes mouth. Other fish, such as gobies (*Elacatinus* spp.), also engage in cleaning.

Quick Facts

Taxon: Labroides dimidiatus

Facts from the source article.

Lore & Background

The bluestreak cleaner wrasse averages 10 cm long, at most 14 cm. It has a wide, longitudinal, black stripe along the side and eye; the back and stomach are white (sometimes slightly yellowish), changing to bright blue on the front, while the black band widens at the tail. Young are black with an electric-blue line. It is found on coral reefs in the tropics from the Red Sea and Indian Ocean to the western Pacific, including Papua New Guinea, Japan, Fiji, and French Polynesia. It was first recorded from the Kermadec Islands Marine Reserve north of New Zealand in 2015, after researchers examined hundreds of hours of unused documentary film footage. Cleaner wrasses occupy cleaning stations, greeting visitors with a dance-like motion. They consume ectoparasites on client fish, which adopt species-specific poses. In some regions, such as the Great Barrier Reef, it is a facultative cleaner that feeds more on corals. In Egypt's Marsa Bareika, it relies on ectoparasites from species like the brown surgeonfish and white belly damselfish. Males defend territories; when the dominant male disappears, a larger female can change sex to take control.

Reader's Guide

The bluestreak cleaner wrasse is a key mutualist on coral reefs, providing cleaning services that remove ectoparasites and dead tissue from client fish. In return, it gains food and protection. Its cleaning behavior is recognized by clients through its lateral stripe and movement patterns. The species shows regional variation in diet: in tidal environments like the Great Barrier Reef, it is a facultative cleaner that feeds more on corals, while in other areas it depends heavily on client parasites. Fish with access to cleaners have better body condition and lower antibody responses, suggesting reduced need for active immunity. The wrasse is mimicked by the blenny Aspidontus taeniatus, which tears flesh instead of cleaning, and by the bluestreak fangblenny Plagiotremus rhinorhynchos, which mimics juveniles to exploit victim concentrations. Genetic analysis suggests the species may be polyphyletic, incorporating two closely related species.

Did You Know?

The bluestreak cleaner wrasse may have passed the mirror test.
It was first recorded in the Kermadec Islands Marine Reserve in 2015 from unused documentary film footage.
In some regions, juvenile bluestreak cleaners bite their clients more often than adults do.
The species may be polyphyletic, incorporating Labroides pectoralis and Labroides bicolor.

A Place Among Six Hundred

The Bluestreak cleaner wrasse belongs to Labridae, one of the most sprawling families in the marine ray-finned fish world. With more than six hundred species distributed across eighty-one genera and eight subfamilies, the family is a vast and colorful assemblage, many of its members wearing vivid coloration. Size within the group varies enormously: the overwhelming majority of wrasses stay under twenty centimeters in length, yet the humphead wrasse stretches to a staggering two and a half meters. Taxonomically, the family has absorbed former relatives; parrotfish, long treated as their own family Scaridae, are now nested deep inside the wrasse phylogenetic tree as a subfamily or tribe. Similarly, the odacine wrasses, once a separate family, turned out to sit within the tribe Hypsigenyini, closest to the tuskfishes. Fossil evidence pushes the family's history back to the Early Eocene of Italy, where several genera—Bellwoodilabrus, Eocoris, Labrobolcus, and others—have been recovered from the Monte Bolca deposits, anchoring Labridae firmly in the ancient Mediterranean landscape.

The Shape of a Mouth

At first glance, a wrasse's face is dominated by a pair of thick, sometimes oddly folded lips—a quirk so distinctive that German and Dutch speakers simply call the group 'lip-fishes.' Behind those lips sits a protractile mouth armed with separate jaw teeth that jut outward, and above the whole structure runs a dorsal fin bearing anywhere from eight to twenty-one spines backed by six to twenty-one soft rays, typically stretching most of the way along the back. But the real engineering marvel lies beneath. The nasal and mandibular bones anchor to the rigid neurocranium at their rear ends, while the maxilla's upper and lower articulations connect to the front tips of those same bones, forming a closed loop of four rigid elements joined by movable joints. This four-bar linkage is mechanically versatile: many different jaw geometries can produce the same outcome, whether that is a rapid protrusion for grabbing prey or a powerful bite. The result is that unrelated wrasse lineages can evolve entirely different jaw shapes yet occupy the same ecological niche with equivalent feeding performance, effectively decoupling form from function.

Two Lives in One Fish

Sex in the wrasse world is far from a simple binary. Most labrids, including the bluestreak cleaner wrasse, are protogynous hermaphrodites: they begin life as functional females within a mixed-sex juvenile cohort, and the largest individuals eventually transform into territory-holding males. This sex change operates inside a haremic mating system, and the family as a whole displays three distinct mating strategies—polygynous, lek-like, and promiscuous—each paired with either group spawning or pair spawning, the choice often tied to male body size. In the laboratory, the plasticity of Labroides dimidiatus becomes vividly apparent. When two adult males are confined to a single tank, the smaller one reverts to female, demonstrating that the sex change is not merely hormonal but responsive to social context. Remarkably, the largest female does not always change; in situations where remaining female yields higher evolutionary fitness, she can effectively 'choose' to stay. A few species, by contrast, show functional gonochorism, being born male or female and never switching.

From Ancient Shores to Tropical Reefs

Today, wrasses are overwhelmingly a tropical and subtropical phenomenon, thriving in the shallow waters of the Atlantic, Indian, and Pacific Oceans around coral reefs and rocky shores, where they hover close to the substrate. A handful of species push into temperate zones; the Ballan wrasse, for instance, ranges as far north as Norway. Yet the family's geographic story stretches much further back and wider than the present. Fossil wrasses have been pulled from the Early Eocene Monte Bolca deposits of Italy, including Phyllopharyngodon, which can be placed within the living subfamily Hypsigenyinae. Even more striking, Middle Eocene remains from the La Meseta Formation of Antarctica show that wrasses once colonized the southernmost continent, a range they presumably lost when the Oligocene cooling made Antarctic waters inhospitable. Within the family, the subfamily Labrinae traces its origins to a basal split during the Eocene, and fifteen of its twenty-three species have evolved broodcare—males building algae nests or crude cavities, ventilating eggs, and defending them against rivals and predators—behavior so essential that in those species the eggs simply cannot survive without it.