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The eastern mosquitofish (''Gambusia holbrooki'') is a
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
, closely related to the western mosquitofish, ''
Gambusia affinis
The western Mosquitofish (''Gambusia affinis'') is a North American freshwater fish, also known commonly, if ambiguously, as simply Mosquitofish or by its generic name, ''Gambusia'', or by the common name gambezi. Its sister species, the easte ...
''. It is a member of the
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Poeciliidae
The Poeciliidae are a family of freshwater fishes of the order Cyprinodontiformes, the tooth-carps, and include well-known live-bearing aquarium fish, such as the guppy, molly, platy, and swordtail. The original distribution of the family was t ...
of
order Cyprinodontiformes
Cyprinodontiformes is an order of ray-finned fish, comprising mostly small, freshwater fish. Many popular aquarium fish, such as killifish and live-bearers, are included. They are closely related to the Atheriniformes and are occasionally inc ...
. The eastern mosquitofish is native to the eastern and southern United States from
Florida
Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...
to
Pennsylvania
Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
and inland to
Alabama
(We dare defend our rights)
, anthem = "Alabama (state song), Alabama"
, image_map = Alabama in United States.svg
, seat = Montgomery, Alabama, Montgomery
, LargestCity = Huntsville, Alabama, Huntsville
, LargestCounty = Baldwin County, Al ...
and
Tennessee
Tennessee ( , ), officially the State of Tennessee, is a landlocked state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to th ...
, while the western mosquitofish has a larger distribution throughout the United States.
Description
The Eastern mosquitofish is a small, light-colored fish with semitransparent fins. The females usually have a black stripe near their eye area and light spots can be seen on the caudal and dorsal fins of both sexes. Due to its similar size, shape, and reproductive habits, it can easily be mistaken for a guppy.
Generally, males reach and females . These fish are a livebearer species, and as such, the females are larger and more rounded than the males. Pregnant females are also easily recognizable by their gravid spot; a darker area on their bellies where they hold the fry.
Mosquitofish may have a melanistic color pattern with black spots, resembling a dalmatian. This could result in its being misidentified as another species.
Similar species
In its native range, Eastern mosquitofish may be confused with the Western Mosquitofish (''Gambusia affin''i''s'') or the sailfin molly (''
Poecilia latipinna
''Poecilia'' is a genus of fishes in the family Poeciliidae of the order Cyprinodontiformes. These livebearers are native to fresh, brackish water, brackish and salt water in the Americas, and some species in the genus are euryhaline. A few have ...
'').
In eastern Australia, the female and juvenile local Pacific blue-eye (''
Pseudomugil signifer
The Pacific blue-eye (''Pseudomugil signifer'') is a species of fish in the subfamily Pseudomugilinae native to eastern Australia. Described by Austrian naturalist Rudolf Kner in 1866, it comprises two subspecies that have been regarded as sepa ...
'') are similar in appearance but have a forked tail fin.
Taxonomy and naming
French naturalist
Charles Frédéric Girard
Charles Frédéric Girard (8 March 1822 – 29 January 1895) was a French biologist specializing in ichthyology and herpetology.
Born in Mulhouse, France, he studied at the College of Neuchâtel, Switzerland, as a student of Louis Agassiz. In ...
described the species in 1859. The genus ''Gambusia'' comes from the Cuban term, "Gambusino", which means "free-lance miner".
[ Common names include eastern mosquitofish, plague minnow and eastern gambusia.] The identity of the person honored in the specific name is uncertain but is thought to be the physician
A physician (American English), medical practitioner (Commonwealth English), medical doctor, or simply doctor, is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through th ...
and naturalist John Edwards Holbrook
John Edwards Holbrook (December 31, 1796 – September 8, 1871) was an American zoologist, herpetologist, physician, and naturalist, born in Beaufort, South Carolina, the son of Silas Holbrook, a teacher, and Mary Edwards. Although Holbrook's memo ...
(1796-1871).
Diet
''G. holbrooki'' is considered a planktivorous
A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton. Planktivorous organisms encompass a range of some of the planet's smallest to largest multicellular animals in both the present day and ...
species which consumes algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
and detritus
In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
. Feeding habits seem to change based on maturity and mating season.[Blanco, S., S. Romo, and M. J. Villena. 2004. Experimental study on the diet of mosquitofish (''Gambusia holbrooki'') under different ecological conditions in a shallow lake. International Review of Hydrobiology 89: 250–262.][McPeek, M. A. 1992. Mechanisms of sexual selection operating on body size in the mosquitofish (''Gambusia holbrooki''). Behavioral Ecology 3: 1-12.] ''Gambusia holbrooki'' will, if need arises, switch food sources to survive. With an increase of competition, this species will switch from a diet rich in phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
, algae, and detritus to one consisting of zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
, invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s, the larvae of many other fish and amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
species, and plant-associated animals. The main source of competition for ''G. holbrooki'' seems to be an increase of its own species and other planktivorous species. The main problem with this is, as mentioned before, it will change its diet; this is common even among the juveniles and both sexes of its own species. The females tend to not specialize on one prey, and consume all evenly, whereas the males and juveniles specialize on one prey type. However. males, females, and juveniles all consume detritus at the same rate.
Habitat and distribution
Eastern mosquitofish are native to the southeastern United States. They have been introduced worldwide and have become an invasive species in many places including Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
and Europe.[
Eastern mosquitofish are found in shallow, standing to slow-flowing water, mostly in vegetated ponds, lakes, and sloughs.][ This species thrives in water between and , and seems to be able to acclimate to temperatures above and below this. ''G. holbrooki'' has been shown to survive in water with pH and chemical levels known to kill other fish species, and prefers to live in areas where the water flows at a slow pace, is clear and without free-floating plant life, and seeks shelter in rooted plants. No decrease in this species due to human activities has been noted.][Pyke, G. H. 2005. A review of the biology of ''Gambusia affinis'' and ''G. holbrooki''. Reviews in Fish Biology and Fisheries. 15: 339–365.] The Eastern mosquitofish is easily maintained and has never been considered an endangered or threatened species due to its ability to thrive in its native habitat. Due to releases in new areas, ''G. holbrooki'' has actually increased its range. It tolerates chemical and thermal changes quite easily.
Life history
Reproduction
Temperature has been shown to change the length of time it takes them to reach reproductive maturity and body size. This species is also known to give birth to live young instead of laying a clutch of eggs.[Mulvey, M., G. P. Keller, and G. K. Meffe. 1994. Single and multiple locus genotypes and life-history responses of ''Gambusia holbrooki'' reared at two temperatures. Evolution. 46: 1810–1819.] The breeding season is between midspring and midautumn, with the peak breeding time being around summer. Females can have up to nine broods per mating season, with the average size ranging from five to 100. The variability of the average brood size is due to many variables, including temperature, age, and available nutrients. Higher temperatures have been shown to increase the fecundity of this species. The gestation period for this species is between 22 and 25 days. Predation stress is also known to affect their reproduction (clutch size). Predator-exposed females were found to give birth to higher number of stillborn offspring compared to unexposed females.[Mukherjee et al. 2014. PLoS ONE 9(2): e88832. doi:10.1371/journal.pone.0088832]
Sexual aggression
According to Pilastro et al. male mosquito fish can be especially sexually aggressive. This aggression can reduce female foraging efficiency by more than half. Females frequently form shoals
In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material and rises from the bed of a body of water to near the surface. It o ...
to reduce sexual harassment from males.[Pilastro et al. 2003]
Female aggregation and male competition reduce costs of sexual harassment in the mosquitofish Gambusia holbrooki
Animal Behavior 65: doi:10.1006/anbe.2003.2118
Growth
The offspring juvenile stage lasts between 18 days and eight weeks. Once again, changes in temperature affects these numbers; colder temperatures decrease and higher temperatures can increase maturity. This species can have several generations within their breeding period because of their fast rate of growth. The usual lifespan is between one and two years, as determined by stress factors in their habitats. Sexual selection in this species is based on the size of the male. Females tend to choose larger, more aggressive males. Females tend to choose areas of shallow water with dark soil cover for brooding sites, while juveniles prefer more rooted plants in which to hide. The main human-induced change that affects the growth rate and life history of ''G. holbrooki'' is the water temperature.
Ecology
Invasive species
Eastern mosquitofish have become an invasive species in Australia
Invasive species in Australia are a serious threat to the native biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variabi ...
. Eastern mosquitofish were introduced into New South Wales in the 1920s to control mosquitoes, but provided no further benefit over small Australian native fish. Further, they cause harm to native species which have an aquatic larval stage. They are aggressive, fin-nipping harassers of other fish, and pose a serious threat to native Australian fish and aquatic fauna. Negative impacts on rainbowfish
The rainbowfish or Melanotaeniidae is a family of small, colourful freshwater fish found in northern and eastern Australia, New Guinea (including islands in Cenderawasih Bay and Raja Ampat Islands in Indonesia), Sulawesi and Madagascar.
The ...
species and at least one frog
A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...
species have been documented. Several rainbowfish populations appear to have become extinct due to the impacts of introduced ''Gambusia''. Compounding the issue, Eastern mosquitofish have the ability to thrive in many different environmental conditions which are usually lethal to other fish species.[Hernandez-Martich, J. D., and M. H. Smith. 1997. Downstream gene flow and genetic structure of ''Gambusia holbrooki'' (eastern mosquitofish) populations. Heredity 79: 295–301.]
Australia set up conservation management plans to try to save native species from ''G. holbrooki''. One such management plan included releasing a chemical known to kill mosquito larvae. The chemicals used were found to have a strong effect on the ''G. holbrooki'', but they became tolerant to most of them fairly rapidly unless amounts considered unsafe for native species were used. Another strategy tried, and failed, to decrease this invasive species was electrifying a lake known to have been invaded. The cost and loss of native fish was so great, this method was dropped. The main reason it failed was these fish stay in the shallows, which receive the smallest charge from the electrification method used. Later tests also revealed this species has a high tolerance for electrical shock, but the exact mechanism that allows this still seems to be questionable.
Predators
Little research has been done to determine all ''G. holbrooki'' predators, due to its own predatory nature in the areas where it has been introduced. In the introduced areas, it has been known to cause top-down trophic effects due to its eating the larvae of some top predators, which include frogs and other fish. Visual exposure to its predator, largemouth bass
The largemouth bass (''Micropterus salmoides'') is a carnivorous freshwater gamefish in the Centrarchidae ( sunfish) family, a species of black bass native to the eastern and central United States, southeastern Canada and northern Mexico, but ...
(''Micropterus salmoides'') is known to affect its reproduction.
References
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{{DEFAULTSORT:Eastern Mosquitofish
Gambusia
Fish described in 1859
Fauna of the Southeastern United States
Fish of North America
Mosquitofish
Live-bearing fish
Freshwater fish of the Southeastern United States