Western mosquitofish

Western mosquitofish
Female
Male
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cyprinodontiformes
Family:	Poeciliidae
Genus:	Gambusia
Species:	G. affinis
Binomial name
Gambusia affinis (Baird and Girard, 1853)

The mosquitofish (Gambusia affinis) 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 (G. holbrooki). Mosquitofish are small in comparison to other fish, with females reaching an overall length of 7 centimeters (2.8 in) and males at a length of 4 centimeters (1.6 in). Females can be distinguished from males by their size and a gravid spot at the posterior of their abdomen. The name "mosquitofish," was given because the diet of this fish predominantly consists of large amounts of mosquito larvae, relative to body size. Mosquitofish were introduced to many parts of the world as a biocontrol to lower mosquito populations. However, such practices appear to be more detrimental to ecosystems than to mosquito population levels.

Fertilization is internal, the male secreting milt into the genital aperture of the female through his gonopodium. Within 16 to 28 days after mating, the female will give birth to about 60 young. 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 in 6 to 7 months.

Description

Mosquitofish are small, dull grey, with a large abdomen, and have rounded dorsal and caudal fins and an upturned mouth towards the surface. Sexual dimorphism is pronounced; mature females reach a maximum overall length of 7 centimeters (2.8 in), while males reach only 4 centimeters (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. Adult female mosquitofish can be identified by a gravid spot they possess on the posterior of their abdomen. Other species that are considered similar to G. affinis include, Poecilia latipinna, Poecilia reticulata, Xiphophorus maculatus, and is commonly misconceived as the eastern mosquitofish.

Naming and Taxonomy

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". The common name, mosquitofish, is derived from their diet, which consist of large amounts of mosquito larvae. 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) is an invalid taxonomic name and is rather a subspecies of G. affinis.

Diet

Mosquito larvae.

Based on diet, mosquitofish are classified as larvivorous fish. The diet of mosquitofish consists of zooplankton, small insects and insect larvae, and detritus material. Mosquitofish feed on mosquito larvae at all stages of life. Adult female mosquitofish can consume in one day hundreds of mosquito larvae. Maximum consumption rate in a day by one mosquitofish has been observed to be from 42%-167% of its own body weight. Mosquitofish have also shown cannibalistic behavior in laboratory experiments, however, whether these traits are hereditary is unknown.

Habitat

The native range of the mosquitofish is from southern parts of Illinois and Indiana, throughout the Mississippi river and it's tributary waters, to as far south as the Gulf Coast in the northeastern parts of Mexico. They are most abundantly found in shallow water protected from larger fish. 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). Because of the mosquitofish's notable adaptability to harsh conditions and their ability to survive in many areas throughout the world, they are considered to be the most widespread freshwater fish. Another contributor to the mosquitofish's pan global occurrence is human intervention, as in biocontrol to lower mosquito populations.

Environmental Impacts

Mosquitofish were intentionally introduced in many areas with large mosquito populations to decrease the population of mosquitoes by eating the mosquito larvae. However, most introductions were ill-advised; in most cases native fish had already proven to supply maximal control of mosquito population and introducing mosquitofish has been more harmful to indigenous aquatic life than to the mosquito population. Introductions outside the mosquitofish's natural range, can be harmful to the nonnative ecosystems. Mosquitofish have been known to kill or injure other small fish by their aggressive behavior and otherwise harm them through competition. Mosquitofish are now considered just slightly better at eating mosquitoes than at destroying other aquatic species. However, from the 1920s to 1950's, mosquitofish were a major factor in the eradication of malaria in South America, in southern Russia and in Ukraine. A somewhat famous example of mosquitofish eradicating malaria is on the coast of the Black Sea located near a city in Russia called Sochi. In Sochi, the mosquitofish is commemorated for eradicating malaria by a monument of the fish. In 2008, in some parts of California, mosquitofish were breed in aquariums so that people could stock stagnant pools of water with the mosquitofish to reduce the number West Nile virus cases.

Reproduction

Reproduction of the mosquitofish starts with the male arranging the rays of the gonopodium (modified anal fin) into a slight tube. The male mosquitofish will use this tubular fin to secrete milt into the female's genital aperture in the process offertilization internal. 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. 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. Inside the female, sperm from multiple males can be stored to later fertilize more ova. Based on laboratory experiments, the female mosquitofish is believed to be vitellogenic in nature during spring when the average temperature reaches about 14 °C (57 °F), and then the oocytes finish maturing 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 lose vitellogenesis. In one reproductive season a female may fertilize, with stored milt, 2 to 6 broods of embryos, with the size of the brood decreasing as the season progresses.

Embryology

Mosquitofish have a 16 to 28 day gestation period. Mosquitofish are lecithotrophic, which means during gestation, nutrients are provided to the embryos by a yolk-sac. If the gestation period is shorter, at birth each newborn will still have a yolk-sac connected through a slit located on the ventral side of the body wall. Female mosquitofish vary on capability of brood size depending on the size of the given female; larger females are more capable of a larger brood quantity than smaller females. Most females though have a brood quantity of about 60 young. Mosquitofish are viviparous, which means after the gestation of a brood the female will have live birth. In most cases the newborn brood will have an equal male to female ratio.

Growth

After birth, newborn mosquitofish are about 8 millimeters (0.31 in) to 9 millimeters (0.35 in) in length. As juveniles, they grow at a rate of about .2 millimeters (0.0079 in) per day. Growth rates of juvenile mosquitofish reach their peak when the water temperature is within a range of 24 °C (75 °F) to 30 °C (86 °F). As temperatures rise above or dip below this range, growth rates decrease. Temperatures at or above 35 °C (95 °F) are typically lethal, while growth stops when temperatures are at or below10 °C (50 °F). For male mosquitofish, sexual maturity is reached in about 43 to 62 days. Female mosquitofish reach sexual maturity in about 21 to 28 days if born early within the reproductive season. The average lifespan for a mosquitofish is less than a year and the maximum lifespan is about 1.5 years. Male mosquitofish lifespans are considerably shorter than the hardier females.

See also

• Mosquitofish in Australia

Bibliography

• Vinogradova, Elena Borisovna (2000). Culex pipiens pipiens mosquitoes: taxonomy, distribution, ecology, physiology, genetic, applied importance and control. Pensoft Publishers. ISBN 9789546421036. http://books.google.com/books?id=770ImWlj3PsC&pg=PA187. Retrieved 29 April 2011. 
• Wallus, Robert; Simon, T.P. (1990). Reproductive Biology and Early Life History of Fishes in the Ohio River Drainage. Taylor & Francis. ISBN 0849319218. 
• Schindler, Joachim; Hamlett, William (1993). Maternal–embryonic relations in viviparous teleosts. Journal of Experimental Zoology. 266. Wiley-Liss, Inc.. pp. 378–393. doi:10.1002/jez.1402660506. http://onlinelibrary.wiley.com/doi/10.1002/jez.1402660506/abstract. Retrieved 31 December 2011. 
• Dionne, Michele (1985). The American Naturalist. 126. The University of Chicago. pp. 16–23. http://www.jstor.org/pss/2461558. Retrieved 11 December 2011. 
• Kuntz, Albert (1913). Notes on the Habits, Morphology of the Reproductive Organs, and Embryology of the Viviparous Fish Gambusia affinis. 33. Department of Commerce. pp. 181–190. http://books.google.com/books?hl=en&lr=&id=E8QWAAAAYAAJ&oi=fnd&pg=PA178-IA7&dq=the+introduction+of+gambusia+affinis&ots=WaOs0UB8Fd&sig=E9kMzgYIZ8sN4q2We3meyfKIvMk#v=onepage&q=the%20introduction%20of%20gambusia%20affinis&f=false. Retrieved 11 December 2011. 
• Rajkumar, R (1987). "Trophic microvilli of the belated embryos of Gambusia affinis (Baird and Girard) (Atheriniformes: Poeciliidae)". Journal of the Inland Fisheries Society of India Barrackpore JINLAND FISHSOCINDIA (1987) (Mendeley) 19 (1): 32–36. http://www.mendeley.com/research/trophic-microvilli-belated-embryos-gambusia-affinis-baird-girard-atheriniformes-poeciliidae-1/. Retrieved 26 December 2011. 
• Krumholz, Louis (30 June 1944). Copeia. No. 2. 1944. American Society of Ichthyologists and Herpetologists. p. 82. http://www.jstor.org/pss/1438757. Retrieved 2 January 2012. 
• Regional Office For The Eastern Mediterranean (2003). Use of Fish For Mosquito Control. World Health Organization. p. 15. http://www.emro.who.int/rbm/publications/fishmanual.pdf. Retrieved 2 January 2012. 
• Campton; Gall (1988). "Effect of individual and group rearing on age and size at maturity of male mosquitofish, Gambusia affinis". Journal of Fish Biology (Wiley Online Library) 33 (2): 203–212. doi:10.1111/j.1095-8649.1988.tb05463.x. http://onlinelibrary.wiley.com/doi/10.1111/j.1095-8649.1988.tb05463.x/abstract. Retrieved 2 January 2012. 

External links

• FishBase: Froese, Rainer, and Daniel Pauly, eds. (2006). "Gambusia affinis" in FishBase. April 2006 version.
• ITIS: Gambusia affinis
• Using Mosquitofish to Control Mosquito Larvae at About.com
• Gambusia Control Homepageaz:Mığmığabalıq