Mosquitofish | |
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Female | |
Male | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
Order: | Cyprinodontiformes |
Family: | Poeciliidae |
Genus: | Gambusia |
Species: | G. affinis |
Binomial name | |
Gambusia affinis (S. F. Baird & Girard, 1853) | |
Synonyms [2] | |
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The western mosquitofish (Gambusia affinis) is a North American freshwater poeciliid 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 eastern mosquitofish ( Gambusia holbrooki ) is also referred to by these names.
Mosquitofish are small in comparison to many other freshwater fish, with females reaching a maximum length of 7 cm (2.8 in) and males a maximum length of 4 cm (1.6 in). The female can be distinguished from the male by her larger size and a gravid spot at the posterior of her abdomen. The name "mosquitofish" was given because the fish eats mosquito larvae, and has been used more than any other fishes for the biological control of mosquitoes. [3] Gambusia typically eat zooplankton, beetles, mayflies, caddisflies, mites, and other invertebrates; mosquito larvae make up only a small portion of their diet. [4]
Mosquitofish were introduced directly into ecosystems in many parts of the world as a biocontrol [5] to lower mosquito populations which in turn negatively affected many other species in each distinct bioregion. [6] Mosquitofish in Australia are classified as a noxious pest and may have exacerbated the mosquito problem in many areas by outcompeting native invertebrate predators of mosquito larvae. Several counties in California distribute mosquitofish at no charge to residents with human-made fish ponds and pools as part of their mosquito abatement programs. [7] [8] [9] The fish are made available to residents only and are intended to be used solely on their own property, not introduced into natural habitat. On 24 February 2014, Chennai Corporation in India introduced western mosquitofish in 660 ponds to control the mosquito population in freshwater bodies. [10]
Fertilization is internal; the male secretes milt into the genital aperture of the female through his gonopodium. [3] [11] Within 16 to 28 days after mating, the female gives birth to about 60 young. [3] [12] The males reach sexual maturity within 43 to 62 days. The females, if born early in the reproductive season, reach sexual maturity within 21 to 28 days; females born later in the season reach sexual maturity the next season, in six to seven months. [13]
Mosquitofish are small and of a dull grey coloring, with a large abdomen, and have rounded dorsal and caudal fins and an upturned mouth. [3] Sexual dimorphism is seen; mature females reach a maximum overall length of 7 cm (2.8 in), while males reach only 4 cm (1.6 in). Sexual dimorphism is also seen in the physiological structures of the body. The anal fins on adult females resemble the dorsal fins, while the anal fins of adult males are pointed. This pointed fin, referred to as a gonopodium, is used to deposit milt inside the female. The gonopodium of G. affinis has a smooth third ray (the anteriormost elongated ray), while that of G. holbrooki bears minute denticles. [14] Adult female mosquitofish can be identified by a gravid spot they possess on the posterior of their abdomens. Other species considered similar to G. affinis include Poecilia latipinna , Poecilia reticulata , and Xiphophorus maculatus ; they are commonly misidentified as mosquitofish. [3] [15]
The mosquitofish is a member of the family Poeciliidae of order Cyprinodontiformes. The genus name Gambusia is derived from the Cuban Spanish term gambusino, meaning "useless". [16] The common name, mosquitofish, is derived from their use for biological control of mosquitoes, which itself was based on early observations that, in certain circumstances, they can reduce mosquito abundances. Classification of the western mosquitofish has been difficult due to their similarity to the eastern mosquitofish, and according to ITIS (Integrated Taxonomic Information System), G. holbrooki (eastern mosquitofish) may be an invalid taxonomic name, and could be considered a subspecies of G. affinis. [3] [17]
Mosquitofish are diet generalists, but they are considered "larvivorous" because they consume the larvae of mosquitoes and other aquatic insects. [18] Their diet consists of zooplankton, small insects and insect larvae, and detritus material. Mosquitofish feed on mosquito larvae at all stages of life, if mosquito larvae are available in the environment. Adult females can consume up to hundreds of mosquito larvae in one day. [3] Maximum consumption rate in a day by one mosquitofish has been observed to be from 42%–167% of its own body weight. [19] However, they can suffer mortality if fed only mosquito larvae, and survivors of this diet show poor growth and maturation. [20] As generalists, mosquitofish have also shown cannibalistic behavior on the young of their own species. [21]
The native range of the mosquitofish is from southern parts of Illinois and Indiana, throughout the Mississippi River and its tributary waters, to as far south as the Gulf Coast in the northeastern parts of Mexico. [22] They are found most abundantly in shallow water protected from larger fish. [11] Mosquitofish can survive relatively inhospitable environments, and are resilient to low oxygen concentrations, high salt concentrations (up to twice that of sea water), and temperatures up to 42 °C (108 °F) for short periods. [15] Because of their notable adaptability to harsh conditions and their global introduction into many habitats for mosquito control, they have been described as the most widespread freshwater fish in the world. [23] Some of their natural predators include the bass, catfish and bluegill. [24]
Mosquitofish were intentionally introduced in many areas with large mosquito populations to decrease the population of mosquitoes by eating the mosquito larvae. [3] However, retrospectively, many introductions could be considered ill-advised; in most cases native fishes supplied control of mosquito populations, and introducing mosquitofish has been harmful to indigenous aquatic life. [23] Mosquitofish introduction outside of their native range can also be harmful to ecosystems. [25] [26] Mosquitofish can consume or injure other small fish or otherwise harm them through competition. [19] The ecological impacts of mosquitofish are partly dictated by their sex ratio, which can vary dramatically across their introduced range. [27] Mosquitofish in Australia are considered noxious pests where they pose a threat to native fish and frog populations and little evidence indicates they have controlled mosquito populations or mosquito-borne diseases. They have been dubbed by scientists as "one of the most problematic animals on the planet". [28]
However, from the 1920s to the 1950s, mosquitofish were considered by some to be a significant factor in eradicating malaria in South America, southern Russia, and Ukraine. Mosquitofish bred by Joice Loch were distributed through Greece, Serbia and the Middle east. [29] On the coast of the Black Sea in Russia, the mosquitofish is commemorated for eradicating malaria by a monument in Sochi. [30]
Mosquitofish are still employed for biological control of mosquitoes in some places. In 2008, in some parts of California and in Clark County, Nevada, mosquitofish were bred in aquariums so people could stock stagnant pools of water with the mosquitofish to reduce the number of West Nile virus cases. [31]
Through species distribution models, it has been revealed that G. affinis exhibit significant niche expansions beyond their natural climatic ranges, with a notable shift towards tropical regions in Asia. [5] These findings highlight the ecological flexibility of these species, contributing to their extensive success and posing a substantial risk for further range expansion. Furthermore, it is assumed that the species will continue to spread in the course of climate change. [5]
Reproduction of the mosquitofish starts with the male arranging the rays of the gonopodium (modified anal fin) into a slight tube. The male mosquitofish uses this tubular fin to secrete milt into the female's genital aperture in the process of internal fertilization. [3] [11] [2] The female's genital aperture is located just behind the anal fin and is an opening for the milt to fertilize the ova within the ovary. [11] Mosquitofish are within the infraclass Teleostei and as all teleosts, mosquitofish lack a uterus, so production of oocytes and gestation occur within the ovary of a female mosquitofish. [32] [33] Inside the female, sperm from multiple males can be stored to later fertilize ova. [3] Based on laboratory experiments, female mosquitofish become vitellogenic when springtime temperatures reach 14 °C (57 °F), and then the oocytes mature when the average temperature reaches about 18 °C (64 °F). Then late in the summer when the photoperiod is less than 12.5 hours long, the next clutch of oocytes develops. [32] In one reproductive season, a female may fertilize, with stored milt, two to six broods of embryos, with the size of the brood decreasing as the season progresses. [13] Reproduction rates are highly dependent on temperature and ration level. As temperature increases from 20 to 30 °C, mean age at first reproduction decreases from 191 to 56 days, and brood size and mass of offspring increase significantly. Interbrood interval estimates at 25 and 30 °C are 23 and 19 days, respectively. [34]
Mosquitofish have a 16- to 28-day gestation period. [12] They are lecithotrophic, which means during gestation, nutrients are provided to the embryos by a yolk sac. [35] If the gestation period is shorter, each newborn will at birth still have a yolk sac connected through a slit located on the ventral side of the body wall. [12] Brood size of females depends on the size of the given female; larger females are more capable of a larger brood quantity than smaller females. Many females have a brood quantity of up to or more than 60 young. [13] [3] Mosquitofish are viviparous, which means after the gestation of a brood, the female will have live birth. [2] [32] In most cases, the newborn brood will have an equal male to female sex ratio. [13]
After birth, newborn mosquitofish are about 8 to 9 mm (0.31 to 0.35 in) in length. As juveniles, they grow at a rate of about 0.2 mm (0.0079 in) per day, but growth is highly temperature-dependent. Growth rates of juvenile mosquitofish reach their peak when the water temperature is within a range of 24 to 30 °C (75 to 86 °F), depending on resource availability. [36] As temperatures rise above or dip below this range, growth rates decrease. Consistent temperatures at or above 35 °C (95 °F) are typically lethal, while growth stops when temperatures are at or below 10 °C (50 °F). [13] For male mosquitofish, sexual maturity is reached in about 43 to 62 days, but maturation age is also dependent on temperature and resources. [37] Female mosquitofish reach sexual maturity in about 21 to 28 days if born early within the reproductive season. The lifespan of a mosquitofish averages less than a year and the maximum is about 1.5 years. However, mosquitofish kept as pets can live much longer, with owners reporting lifespans of over three years. Male mosquitofish lifespans are considerably shorter than females. [13]
Poeciliidae are a family of freshwater ray-finned 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 the Southeastern United States to north of Río de la Plata, Argentina, and Africa, including Madagascar. Due to release of aquarium specimens and the widespread use of species of the genera Poecilia and Gambusia for mosquito control, though, poeciliids can today be found in all tropical and subtropical areas of the world. In addition, Poecilia and Gambusia specimens have been identified in hot springs pools as far north as Banff, Alberta.
Gambusia is a large genus of viviparous fish in the family Poeciliidae. Gambusia contains over 40 species, most of which are principally found in freshwater habitats, though some species may also be found in brackish or saltwater habitats. The genus Gambusia comes from the Cuban term, "Gambusino", which means "free-lance miner". The type species is the Cuban gambusia, G. punctata. The greatest species richness is in Mexico, Texas, and the Greater Antilles, but species are also found elsewhere in the eastern and southern United States, the Bahamas, Central America, and Colombia. Gambusia species are often called topminnows, or simply gambusias; they are also known as mosquitofish, which, however, refers more specifically to two species, G. affinis and G. holbrooki, which are often introduced into ponds to eat mosquito larvae. As a consequence, they have been introduced widely outside their native range, and frequently become invasive, threatening local species. G. affinis and G. holbrooki are now established in many parts of the world and are likely to continue to spread as climatic conditions change. They are only occasionally kept in aquariums, due to their relative lack of color and the highly aggressive nature of the aforementioned mosquitofish species.
The sailfin molly is a livebearer fish typically found in both freshwater and brackish waterways along the East Coast of the United States, from North Carolina south to Florida, and around the Gulf of Mexico to Texas, and south to the Yucatán Peninsula of México. Given their preference for more brackish water conditions, mollies are often found within just a few yards or miles of the ocean, inhabiting coastal estuaries, lagoons, river deltas and swamps, as well as tidal areas with a regular inflow of oceanic minerals and nutrients mixing with inland freshwater sources.
Fish reproductive organs include testes and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused. There may also be a range of secondary organs that increase reproductive fitness. The genital papilla is a small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish can often be determined by the shape of its papilla.
The Shoshone pupfish is a subspecies of Amargosa pupfish from California in the United States. They are spring-dwelling fish, endemic to Shoshone Springs on the outskirts of Shoshone, Inyo County, California. In 1969, the Shoshone pupfish was declared extinct until their eventual rediscovery by a team of biologists during a survey of Shoshone Springs in 1986. Currently, they are listed as endangered by the American Fisheries Society and are a species of special concern according to the California Department of Fish and Wildlife. Several stocks of the fish are being cultivated in captivity at the University of Nevada, Las Vegas and University of California, Davis for reintroduction into the Shoshone Spring. Today, people pass through the town of Shoshone to visit the spring site and view the rare pupfish, where some infographics and signs educate visitors about them.
Nomorhamphus is a southeast Asian genus of viviparous halfbeaks from streams, rivers and lakes in Sulawesi (Indonesia) and the Philippines. They are all viviparous, producing small clutches of around a dozen fry about 10 to 15 mm long at birth. Females are generally larger than the males. In the largest species, such as Nomorhamphus liemi, the females typically reach about 10 centimetres (3.9 in) in length, whereas the males reach about 6–7 cm (2.4–2.8 in) in length. Males are also more brightly coloured than the females. Compared with many other halfbeaks, the lower mandible, or beak, is relatively short, on females in particular barely protruding beyond the length of the upper mandible. The males of some species have short, straight beaks, but those of others have short beaks that curve downwards forming a shape often compared to a goatee beard by aquarists. N. aenigma is unique within Nomorhamphus because of its lack of lower jaw elongation.
The eastern mosquitofish is a species of freshwater fish, closely related to the western mosquitofish, Gambusia affinis. It is a member of the family Poeciliidae of order Cyprinodontiformes. The eastern mosquitofish is native to the eastern and southern United States from Florida to Pennsylvania and inland to Alabama and Tennessee, while the western mosquitofish has a larger distribution throughout the United States.
The Spanish toothcarp, also known as the Spanish toothcarp or Iberian killifish, is a small, endemic species of fish in the family Aphaniidae. Its risk of extinction is one of the greatest of any Iberian vertebrate. Its limited range, coupled with the drastic population decline the species has suffered in the last two decades, has caused it to be placed on endangered species lists, both in Spain and internationally. In addition, habitat fragmentation, likely due to humans, has resulted in this species becoming increasingly stagnant and has led to increased genetic drift. Also found to be contributing to their endangerment was genetic diversity of mitochondrial DNA. The mitochondrial DNA coupled with A. iberus’s geographic distribution has been able to affect their population genetic structure gradually in different spaces. Its conservation status in the south of the Iberian Peninsula has notably worsened.
The least chub is a species of ray-finned fish in the family Cyprinidae, the only member of the genus Iotichthys. This species is found only in Utah and more recently in Idaho in the United States. Due to habitat degradation and introduction of non-native fishes, it is currently limited to a few spring complexes in Utah and the Snake River Valley in Idaho.
The Gila topminnow or charalito is a species of fish in the family Poeciliidae. It is found in Mexico and the United States.
Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, to spawn refers to the process of freely releasing eggs and sperm into a body of water ; the physical act is known as spawning. The vast majority of aquatic and amphibious animals reproduce through spawning. These include the following groups:
The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes of differentiated species often have significant differences. These differences allow for a combination of genetic material between two individuals, which allows for the possibility of greater genetic fitness of the offspring.
The dusky millions fish, speckled mosquitofish or the one-spot livebearer is a species of fish native eastern and southern Brazil, northern Argentina, Uruguay and Paraguay. It has also been introduced to Australia, Malawi and New Zealand; primarily for mosquito control, but also as escapees from the aquarium trade. It has been reported as having adverse ecological effects in areas where it has been introduced. The females of this species grow to a total length of 6 centimetres (2.4 in), while males remain smaller.
The Yaqui topminnow is a species of fish in the family Poeciliidae. Its scientific name is Poeciliopsis sonoriensis; it is also sometimes considered a subspecies of Poeciliopsis occidentalis as P. o. sonoriensis. This fish is native to Mexico and the United States, with a few native and introduced populations persisting in Arizona in the United States, and a number of populations still extant in northern Sonora, Mexico.
The eastern mosquitofish was introduced to Australia in 1925, and had spread from the northeast coasts to New South Wales, southern Australia, and parts of Western Australia by 1934. By the 21st century, known populations of wild mosquitofish had occurred in every state and territory except the Northern Territory, found in swamps, lakes, billabongs, thermal springs, salt lakes, and ornamental ponds. Mosquitofish are considered a noxious pest, especially in New South Wales and Queensland, and it is illegal to release them into the wild or transport them live into any of the states or territories. Mosquitofish were introduced by military and local councils to control mosquito populations; however, there has been no evidence that Gambusia has had any effect in controlling mosquito populations or mosquito-borne diseases. Studies have shown that Gambusia can suffer mortalities if fed only on mosquito larvae, and survivors show poor growth and maturation. Gambusia typically eat zooplankton, beetles, mayflies, caddis flies, mites and other invertebrates; mosquito larvae make up only a small portion of their diet.
Melanotaenia duboulayi, the crimson-spotted rainbowfish, less commonly known as the Duboulay's rainbowfish, is a species of freshwater fish endemic to coastal eastern Australia, although M. duboulayi has also been kept as an aquarium fish since the early 20th century, and is the original "Australian rainbowfish".
Zenarchopteridae, the viviparous halfbeaks, is a family in the order Beloniformes. The Zenarchopteridae exhibit strong sexual dimorphism, practicing internal fertilisation, and in some cases ovoviviparous or viviparous. The members in the family are mainly found in fresh and brackish water of tropical Asia and New Guinea, but the genus Zenarchopterus also includes marine species from the Indo-Pacific. Several, such as the wrestling halfbeak, have become commonly traded aquarium fish.
Pregnancy has been traditionally defined as the period of time eggs are incubated in the body after the egg-sperm union. Although the term often refers to placental mammals, it has also been used in the titles of many international, peer-reviewed, scientific articles on fish, e.g. Consistent with this definition, there are several modes of reproduction in fish, providing different amounts of parental care. In ovoviviparity, there is internal fertilization and the young are born live but there is no placental connection or significant trophic (feeding) interaction; the mother's body maintains gas exchange but the unborn young are nourished by egg yolk. There are two types of viviparity in fish. In histotrophic viviparity, the zygotes develop in the female's oviducts, but she provides no direct nutrition; the embryos survive by eating her eggs or their unborn siblings. In hemotrophic viviparity, the zygotes are retained within the female and are provided with nutrients by her, often through some form of placenta.
Hypseleotris compressa, the empire gudgeon, is a species of Gobiiform fish in the family Eleotridae endemic to Australia and south-central New Guinea.
Poeciliinae is a subfamily of killifish from the family Poeciliidae which contains species from the Americas which are collectively known as the livebearers because many, but not all, of the species within the subfamily are ovoviviparous.
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