Mosquitofish in Australia
Encyclopedia
Mosquitofish
(Gambusia affinis) were introduced to Australia
in 1925, spreading from the northeast coasts south to New South Wales, Southern Australia, and parts of Western Australia by 1934. Currently, known populations of wild mosquitofish occur in every state and territory except the Northern Territory, and they are 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. In fact, 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.
Many ichthyologists
believe native species are more effective in population control than mosquitofish. These include species such as the western minnow and pygmy perches. Unfortunately, gambusia may have exacerbated the mosquito problem in many areas by outcompeting native invertebrate predators of mosquito larvae. Because of their aggressive nature and high birthrate, mosquitofish can overtake most native species in an area, drastically harming local populations. Even if they were needed for mosquito control, studies have also shown that at least 5,000 fish/ha would be needed for effective control. However, mosquitoes' breeding environments are migratory and unreliable, so regular fish predators can have little effect from year to year.
Mosquitofish have a high tolerance for salinity, low oxygen, extreme temperatures (from 0.5-35°C), and pollutants, and are therefore able to live in many areas where other fish cannot. Certain thermal adaptations have allowed them to live in places from 55° North
to 44° South
, expanding their natural range. They have a resistance to a wide variety of pollutants, including organic waste, heavy metals, insecticides, herbicides, rotenone, phenol, and radiation. Ichthyologists believe the reason for low mosquito levels in areas populated by gambusia is not because of the fish, but rather the insecticide in the water killing the larvae.
Mosquitofish have harmed native fish populations in many ways. By consuming algae-eating zooplankton, they increase the chances of algae blooms in the water, reducing the water quality. They are very aggressive, and tend to attack other fish and nip their fins, leading to infection or death. Studies have shown that the purple spotted gudgeon fish population has declined as a result of high densities of mosquitofish. They have also negatively impacted populations of beetles, backswimmers, rotifer
s, red finned blue eye, Edgbast goby, crustacean
s and mollusks, to name a few. In a study done by Keane et al., 2004, one major threat to Tasmanian fauna could be to native galaxiids, as suggested by the fact that mosquitofish are known to attack and kill adult Galaxias gracilis
in New Zealand. If gambusia became native in certain areas by eradicating other fish populations, it could put a great deal of stress on the remaining flora and fauna. Decreasing the number of native species would also benefit mosquitoes by decreasing the competitive pressure from other fish. Because of their high reproductive rate (an average of 50 young per brood, with up to nine broods per year), fast maturation (sexual maturity is reached in two months), and aggressive behaviour, mosquitofish can outcompete almost any native fish.
Mosquitofish also pose a threat to populations of native frogs (such as Limnodynastes ornatus) in natural water bodies where these species co-occur. In one study conducted by Keane et al., gambusia consumed the tadpoles of L. ornastus, leading researchers to believe that over a period of time, they could wipe out the L. ornastus population as a whole. Gambusia are known predators of tadpoles of other closely related frog species, such as L. aurea and L. dentate. The green and golden bellfrog in Tasmania is now directly threatened by gambusia, and is listed on Tasmania’s Threatened Species Protection Act of 1995. Another study conducted by Keane found that tadpoles are better suited to environments without introduced fish. Responses observed in the green and golden bellfrog suggest that tadpoles are naïve to mosquitofish because they did not respond to them. Additionally, gambusia and other introduced fish may have reduced the suitability of permanent water bodies as breeding sites for pond-breeding amphibian species such as the green and golden bellfrog.
One species of fish, the Edgbaston hardyhead, is restricted to one spring-fed pool in the Edgbaston Spring Complex located in Edgbaston Station, central Queensland. The hardyhead competes with the mosquitofish for food and resources; if the mosquitofish outcompetes the hardyhead, they will have eradicated an entire species in one fell swoop. That is why the hardyhead is now considered a high priority for conservation recovery actions in Queensland, where steps are now being taken to exterminate the mosquitofish from the spring.
The mosquitofish was nominated as an environmental hazard under the NSW Threatened Species Conservation Act in 1999, making it illegal for landowners to do anything that would help spread gambusia. This includes releasing mosquitofish pets into the wild, one of the biggest problems affecting local rivers throughout eastern Australia. Proposals for gambusia population control have included introducing viral, bacterial, or fungal diseases and parasites into an overpopulated area. However, many diseases can jump species and would harm native fish. The Tasmanian government has taken steps to eradicate mosquitofish by containing current populations and minimizing paths of dispersal. In Gordon’s Lagoon at the Clarkesdale Bird Sanctuary
in Linton, Victoria
, which experiences major infestations of mosquitofish year-round, park managers have taken advantage of recent dry conditions by draining ponds. Residual wet areas are treated with lime solutions, changing the pH of the water and killing off the fish. Other ideas have been proposed, but attempting to isolate them to affect only the mosquitofish is unrealistic as of yet. Gambusia also thrive due to their habits of consuming faecal matter and general organic waste.
Mosquitofish
The mosquitofish is a species of freshwater fish, also commonly, if ambiguously, known by its generic name, gambusia. It is sometimes called the western mosquitofish, to distinguish it from the eastern mosquitofish . It is a member of the family Poeciliidae of order Cyprinodontiformes...
(Gambusia affinis) were introduced to Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
in 1925, spreading from the northeast coasts south to New South Wales, Southern Australia, and parts of Western Australia by 1934. Currently, known populations of wild mosquitofish occur in every state and territory except the Northern Territory, and they are 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. In fact, 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.
Many ichthyologists
Ichthyology
Ichthyology is the branch of zoology devoted to the study of fish. This includes skeletal fish , cartilaginous fish , and jawless fish...
believe native species are more effective in population control than mosquitofish. These include species such as the western minnow and pygmy perches. Unfortunately, gambusia may have exacerbated the mosquito problem in many areas by outcompeting native invertebrate predators of mosquito larvae. Because of their aggressive nature and high birthrate, mosquitofish can overtake most native species in an area, drastically harming local populations. Even if they were needed for mosquito control, studies have also shown that at least 5,000 fish/ha would be needed for effective control. However, mosquitoes' breeding environments are migratory and unreliable, so regular fish predators can have little effect from year to year.
Mosquitofish have a high tolerance for salinity, low oxygen, extreme temperatures (from 0.5-35°C), and pollutants, and are therefore able to live in many areas where other fish cannot. Certain thermal adaptations have allowed them to live in places from 55° North
55th parallel north
The 55th parallel north is a circle of latitude that is 55 degrees north of the Earth's equatorial plane. It crosses Europe, Asia, the Pacific Ocean, North America, and the Atlantic Ocean....
to 44° South
44th parallel south
The 44th parallel south is a circle of latitude that is 44 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, the Indian Ocean, Australasia, the Pacific Ocean and South America....
, expanding their natural range. They have a resistance to a wide variety of pollutants, including organic waste, heavy metals, insecticides, herbicides, rotenone, phenol, and radiation. Ichthyologists believe the reason for low mosquito levels in areas populated by gambusia is not because of the fish, but rather the insecticide in the water killing the larvae.
Mosquitofish have harmed native fish populations in many ways. By consuming algae-eating zooplankton, they increase the chances of algae blooms in the water, reducing the water quality. They are very aggressive, and tend to attack other fish and nip their fins, leading to infection or death. Studies have shown that the purple spotted gudgeon fish population has declined as a result of high densities of mosquitofish. They have also negatively impacted populations of beetles, backswimmers, rotifer
Rotifer
The rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John Harris in 1696, and other forms were described by Anton van Leeuwenhoek in 1703...
s, red finned blue eye, Edgbast goby, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s and mollusks, to name a few. In a study done by Keane et al., 2004, one major threat to Tasmanian fauna could be to native galaxiids, as suggested by the fact that mosquitofish are known to attack and kill adult Galaxias gracilis
Dwarf inanga
The dwarf inanga, Galaxias gracilis, is a galaxiid of the genus Galaxias, found in the North Island of New Zealand.It is a landlocked galaxiid present in only 11 lakes on the west coast of the North Island within 50 km of Dargaville, and in Lake Ototoa on the South Kaipara Head, where it was...
in New Zealand. If gambusia became native in certain areas by eradicating other fish populations, it could put a great deal of stress on the remaining flora and fauna. Decreasing the number of native species would also benefit mosquitoes by decreasing the competitive pressure from other fish. Because of their high reproductive rate (an average of 50 young per brood, with up to nine broods per year), fast maturation (sexual maturity is reached in two months), and aggressive behaviour, mosquitofish can outcompete almost any native fish.
Mosquitofish also pose a threat to populations of native frogs (such as Limnodynastes ornatus) in natural water bodies where these species co-occur. In one study conducted by Keane et al., gambusia consumed the tadpoles of L. ornastus, leading researchers to believe that over a period of time, they could wipe out the L. ornastus population as a whole. Gambusia are known predators of tadpoles of other closely related frog species, such as L. aurea and L. dentate. The green and golden bellfrog in Tasmania is now directly threatened by gambusia, and is listed on Tasmania’s Threatened Species Protection Act of 1995. Another study conducted by Keane found that tadpoles are better suited to environments without introduced fish. Responses observed in the green and golden bellfrog suggest that tadpoles are naïve to mosquitofish because they did not respond to them. Additionally, gambusia and other introduced fish may have reduced the suitability of permanent water bodies as breeding sites for pond-breeding amphibian species such as the green and golden bellfrog.
One species of fish, the Edgbaston hardyhead, is restricted to one spring-fed pool in the Edgbaston Spring Complex located in Edgbaston Station, central Queensland. The hardyhead competes with the mosquitofish for food and resources; if the mosquitofish outcompetes the hardyhead, they will have eradicated an entire species in one fell swoop. That is why the hardyhead is now considered a high priority for conservation recovery actions in Queensland, where steps are now being taken to exterminate the mosquitofish from the spring.
The mosquitofish was nominated as an environmental hazard under the NSW Threatened Species Conservation Act in 1999, making it illegal for landowners to do anything that would help spread gambusia. This includes releasing mosquitofish pets into the wild, one of the biggest problems affecting local rivers throughout eastern Australia. Proposals for gambusia population control have included introducing viral, bacterial, or fungal diseases and parasites into an overpopulated area. However, many diseases can jump species and would harm native fish. The Tasmanian government has taken steps to eradicate mosquitofish by containing current populations and minimizing paths of dispersal. In Gordon’s Lagoon at the Clarkesdale Bird Sanctuary
Clarkesdale Bird Sanctuary
The Clarkesdale Bird Sanctuary is a nature reserve focused on protecting and restoring habitat for woodland birds. It lies in the state of Victoria in south-eastern Australia, near the small town of Linton, 30 km south-west of the city of Ballarat.-History:...
in Linton, Victoria
Linton, Victoria
Linton is a town in Victoria, Australia off Glenelg Highway. It was first settled about 1840. The town was named after a pioneer family in an area. At the 2006 census, Linton had a population of 355. The Clarkesdale Bird Sanctuary lies to the south-east of the township, near Springdallah Creek.-...
, which experiences major infestations of mosquitofish year-round, park managers have taken advantage of recent dry conditions by draining ponds. Residual wet areas are treated with lime solutions, changing the pH of the water and killing off the fish. Other ideas have been proposed, but attempting to isolate them to affect only the mosquitofish is unrealistic as of yet. Gambusia also thrive due to their habits of consuming faecal matter and general organic waste.
See also
- Invasive species in AustraliaInvasive species in AustraliaInvasive species are a serious threat to the native biodiversity of Australia and are an ongoing cost to Australian agriculture.Management and the prevention of the introduction of new invasive species are key environmental and agricultural policy issues for the Australian federal and state...
- Conservation in AustraliaConservation in AustraliaConservation in Australia is an issue of state and federal policy. Australia is one of the most biologically diverse countries in the world, with a large portion of species endemic to Australia...
- Environmental issues in AustraliaEnvironmental issues in AustraliaEnvironmental issues in Australia describes a number of environmental issues which affect the environment of Australia. There are a range of such issues, some of them relating to conservation in Australia while others, for example the deteriorating state of Murray-Darling Basin, have a direct and...
- Gambusia affinis
- Gambusia holbrooki