Gill raker
Encyclopedia
Gill rakers in fish are bony
or cartilaginous processes that project from the branchial arch
(gill arch) and are involved with filter feeding tiny prey. They are not to be confused with the gill filaments that compose the bony part of the gill. Rakers are usually present in two rows, projecting from both the anterior and posterior side of each gill arch. Rakers are widely varied in number, spacing, and form. By preventing food particles from exiting the spaces between the gill arches, they enable the retention of food particles in filter feeders.
The structure and spacing of gill rakers in fish determines the size of food particles trapped, and correlates with feeding behavior. Fish with densely spaced, elongated, comb-like gill rakers are efficient at filtering tiny prey, whereas carnivores and omnivores often have more widely spaced gill rakers with secondary projections. Because gill raker characters often vary between closely related taxa, they are commonly used in the classification and identification of fish species. Much of the variation in gill raker morphology is thought to be due to adaptation to optimize the consumption of different diets.
In order to prevent the potentially damaging passage of solid material through the gill slits and over the gill filaments, early gill rakers strained large particles from the water and diverted them to the esophagus
. Since an appreciable fraction of this material was nutritious, rakers subsequently evolved as food-trapping mechanisms in filter feeders. Gill rakers, when long and closely set, play the same role in filter-feeding fish such as mullet
, herring
, Megamouth
, Basking
and Whale shark
s, as baleen
in the filter-feeding whales.
Gill rakers in land-dwelling and mangrove crabs are feather-like structures which brush moisture over the gills to prevent their dehydration and ensure their ability to absorb oxygen. These gill rakers are not thought be homologous to fish gill rakers.
Bony
Bony may refer to:* Adjective related to bone* Bony, a commune of the Aisne département, in France* Bőny, a village in Hungary* A nickname for Napoleon Bonaparte* The Bank of New York...
or cartilaginous processes that project from the branchial arch
Branchial arch
In the development of vertebrate animals, the pharyngeal arches are anlage for a multitude of structures. In humans, they develop during the fourth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx...
(gill arch) and are involved with filter feeding tiny prey. They are not to be confused with the gill filaments that compose the bony part of the gill. Rakers are usually present in two rows, projecting from both the anterior and posterior side of each gill arch. Rakers are widely varied in number, spacing, and form. By preventing food particles from exiting the spaces between the gill arches, they enable the retention of food particles in filter feeders.
The structure and spacing of gill rakers in fish determines the size of food particles trapped, and correlates with feeding behavior. Fish with densely spaced, elongated, comb-like gill rakers are efficient at filtering tiny prey, whereas carnivores and omnivores often have more widely spaced gill rakers with secondary projections. Because gill raker characters often vary between closely related taxa, they are commonly used in the classification and identification of fish species. Much of the variation in gill raker morphology is thought to be due to adaptation to optimize the consumption of different diets.
In order to prevent the potentially damaging passage of solid material through the gill slits and over the gill filaments, early gill rakers strained large particles from the water and diverted them to the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
. Since an appreciable fraction of this material was nutritious, rakers subsequently evolved as food-trapping mechanisms in filter feeders. Gill rakers, when long and closely set, play the same role in filter-feeding fish such as mullet
Mullet (fish)
The mullets or grey mullets are a family and order of ray-finned fish found worldwide in coastal temperate and tropical waters, and in some species in fresh water. Mullets have served as an important source of food in Mediterranean Europe since Roman times...
, herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, Megamouth
Megamouth shark
The megamouth shark, Megachasma pelagios, is an extremely rare species of deepwater shark. Since its discovery in 1976, only a few megamouth sharks have been seen, with 53 specimens known to have been caught or sighted as of 2011, including three recordings on film...
, Basking
Basking shark
The basking shark is the second largest living fish, after the whale shark. It is a cosmopolitan migratory species, found in all the world's temperate oceans. It is a slow moving and generally harmless filter feeder and has anatomical adaptations to filter feeding, such as a greatly enlarged...
and Whale shark
Whale shark
The whale shark, Rhincodon typus, is a slow-moving filter feeding shark, the largest extant fish species. The largest confirmed individual had a length of and a weight of more than , but unconfirmed claims report considerably larger whale sharks...
s, as baleen
Baleen
Baleen or whalebone is a filter-feeder system inside the mouths of baleen whales. The baleen system works when a whale opens its mouth underwater and then water pours into the whale's mouth. The whale then pushes the water out, and animals such as krill are filtered by the baleen and remain as food...
in the filter-feeding whales.
Gill rakers in land-dwelling and mangrove crabs are feather-like structures which brush moisture over the gills to prevent their dehydration and ensure their ability to absorb oxygen. These gill rakers are not thought be homologous to fish gill rakers.