Wrasse

The wrasses are a massive and diverse family of marine fish known scientifically as Labridae. This family contains over 600 different species organized into 81 genera. These fish are found in many different environments across the globe. Most inhabit the tropical and subtropical waters of the Atlantic, Indian, and Pacific Oceans. However, some species can handle cooler temperatures. For example, the Ballan wrasse lives as far north as Norway.

While most wrasses are quite small, they show incredible variety in size and appearance.

One of the most fascinating aspects of wrasse biology is their complex jaw structure. Scientists study them to understand fish-feeding biomechanics. Their mouths are protractile, meaning they can extend outward. This movement is possible because of a mechanical system called a "four-bar linkage." In this system, the nasal and mandibular bones connect to the rigid neurocranium. The maxilla bones then join to the tips of these bones. This creates a loop of four rigid bones held by moving joints. This setup allows them to achieve fast protrusion or a very forceful bite.

Many wrasses exhibit unusual reproductive behaviors and developmental systems. Many species are protogynous hermaphrodites, which means they can change sex from female to male. This usually happens within a haremic mating system. In these groups, juveniles are often "initial-phase" individuals of mixed sexes. As they grow, the largest adults become "terminal-phase" males that hold territory. While sex change is generally female-to-male, experiments show it can go the other way. If two male bluestreak cleaner wrasses are placed together, the smaller one can become female again.

There are several different ways wrasses handle reproduction and care. Some species use broadcast spawning, where they release many planktonic eggs into tidal currents. In these cases, the adults do not interact with their offspring. However, the subfamily Labrinae is different. This group includes genera like Symphodus, Centrolabrus, and Labrus. These fish exhibit broodcare behavior, which is a form of parental care. Males in these species may build nests out of algae or crude cavities. They will also ventilate the eggs and defend the nests from predators. Without this parental care, the eggs would not survive.

Taxonomy, or the way we classify these fish, has changed over time. For a long time, parrotfish were considered their own family called Scaridae. Scientists now recognize them as a subfamily, Scarinae, within the wrasse family. Similarly, odacine wrasses were once thought to be a separate family. We now know they are nested within the wrasse tribe Hypsigenyini. They are most closely related to tuskfishes. The family is divided into eight subfamilies, including Hypsigenyinae, Cirrhilabrinae, and Labrinae.

Some wrasses are incredibly intelligent and use tools to eat. Twenty-one species across eight different genera have been seen using "anvils." They use large rocks or hard coral to smash open hard-shelled prey. This includes animals like clams, crabs, and sea urchins. In one surprising instance, a blue tuskfish was observed smashing a young green sea turtle on an anvil.

Other wrasses, like the bluestreak cleaner wrasse, participate in a cleaning symbiosis. They act as cleaners at "cleaning stations" on coral reefs. They eat parasites, dead tissue, and scales off larger "client" fish. This relationship helps the client stay healthy and provides the wrasse with food.

We can learn about the history of these fish through fossils. Fossil wrasses have been found dating back to the Early Eocene in Monte Bolca, Italy. One fossil genus, Phyllopharyngodon, belongs to the Hypsigenyinae subfamily. Wrasses also had a very wide distribution in the prehistoric past. Fossil remains have been discovered in the La Meseta Formation of Antarctica. These fish likely disappeared from Antarctica when the continent cooled during the Oligocene.

Humans have many connections to the wrasse family. In the Western Atlantic, indigenous people used the tautog as a common food source. Today, wrasses are popular in both home and public aquariums. They are also very useful in modern industry. In Scotland, cleaner wrasses are used in commercial salmon farming. They act as "lice busters" by eating sea lice that infest the salmon. This provides a significant commercial benefit to fish farmers.