Gambusia affinis

The mosquitofish (Gambusia affinis) is a species of freshwater fish in the family Poeciliidae, native to the Mississippi River (USA) and its tributary waters from southern Indiana and Illinois to the Gulf Coast and parts of northeastern Mexico. It is commonly known by its generic name, gambusia, and sometimes called the western mosquitofish to distinguish it from the closely related eastern mosquitofish (G. holbrooki), which according to ITIS is actually a subspecies of G. affinis, rather than its own species; this has complicated classification of G. affinis). The name "mosquitofish" was given because the diet of this fish predominantly consists of large amounts of mosquito larvae (as well as other invertebrate larvae); an adult female can consume hundreds in a day. Hardy to a variety of temperatures, salinities and oxygen levels, mosquitofish have spread through many parts of the world in introductions attempting to reduce mosquito populations. Although this biocontrol did play a major role in containing malaria in South America, Russia and the Ukraine in the 1920s, they are now recognized the Global Invasive Species Database as one of the world’s 100 worst invasive species. This voracious, aggressive predator has extirpated and eliminated many native species, is extremely hard to eradicate, and is now a pest in fresh and brackish waters around the world. Mosquitofish are small; females reach an overall length of 7 centimeters and males at a length of 4 centimeters (1.6 in). Like all other New World members of this family, G. affinis gives birth to live young.

(Froese and Pauly 2011; ITIS 2011; IUCN/SSC Invasive Species Specialist Group 2010; Wikipedia 2012)

Most abundant in lower reaches of streams (Ref. 44091). Adults inhabit standing to slow-flowing water; most common in vegetated ponds and lakes, backwaters and quiet pools of streams. Found frequently in brackish water (Ref. 5258). Feed on zooplankton, small insects and detritus (Ref. 5258, 10294). Used as live food for carnivorous aquarium fishes. Viviparous (Ref. 5258, 30578). Effective in mosquito control and widely introduced, but found to compete with indigenous fish and to upset the ecological balance (Ref. 6351).

The mosquitofish, Gambusia affinis , is a small, robust-bellied fish. The relatively large head is flattened on the upper surface, and the small mouth is superior (upturned) and protrusible. The eyes are large relative to the body. Dorsal and caudal fins are rounded and no lateral line is visible (IGGS 2006).The body is usually greenish olive to brown above, grey-blue on the sides, and silvery-white below. The body has a characteristic diamond or net pattern on the body formed by dark pigment at the scale margins. Small black dots are also usually present on the body and tail. A small dark bar below the eye also aids in identification and a black peritoneum (abdominal cavity lining) can often be observed through the belly in living specimens. Melanistic (black or nearly black) individuals are common in some populations. The dorsal fin is single and has only soft rays. Individuals typically have 7-9 soft dorsal rays, 8-10 anal fins, and 29-32 lateral line scales (Hoese and Moore 1977, Robins et al 1986, IGGS 2006).The species is sexually dimorphic, with adult males being considerably smaller than females and also possessing a gonopodium-an elongated anal fin that functions as an intromittent organ for sperm transfer during mating. Mature females have a distinct gravid spot located on the posterior abdomen above the rear of the anal fin (Hoese and Moore 1977, GLAVCD undated).

Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) This species is native to most of south-central United States, north to Indiana and Illinois, west to Texas, south to southern Mexico, east to Mobile River system. Populations in the drainages of the Chattahoochee and Savannah rivers (Lydeard and Wooten 1991) possibly are native (Page and Burr 2011). See Walters and Freeman (2000) for information on the distribution of G. affinis and G. holbrooki in the Conasauga River system, where G. affinisi is widespread and native and G. holbrooki is apparently introduced and expanding its range. This fish is widely introduced in the western United States and throughout the world.

Lynch (1992) reported that five or six populations from Georgia, Illinois, Tennessee and Texas were used for most introductions nationwide and worldwide. Within the United States, sources from Illinois, Tennessee and Texas were used to establish mosquitofish in the western half of the country. Therefore, most if not all populations in the western United States are G. affinis.

North and Central America: Mississippi River basin from central Indiana and Illinois in USA south to Gulf of Mexico and Gulf Slope drainages west to Mexico. One of the species with the widest range of introductions which acquired for itself a near pan-global distribution (Ref. 1739). Several countries report adverse ecological impact after introduction.

North and Central America: Mississippi River basin from central Indiana and Illinois in USA south to Gulf of Mexico and Gulf Slope drainages west to Mexico. One of the species with the widest range of introductions which acquired for itself a near pan-global distribution. N.J. to s. Florida and around n. Gulf Coast of Texas.

Gulf of Mexico, New Zealand Exclusive Economic Zone, North West Atlantic

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Gambusia affinis is native to fresh/low-salinity waters of the eastern and southeastern US and Gulf of Mexico, from New Jersey to central Mexico (Hoese and Moore 1977). They may be found in fresh water as far inland as Illinois (Ray et al. 1986).Mosquitofish now also occur throughout much of the world as a result of intentional and non-intentional introductions beginning approximately 100 years ago. Intentional introductions have largely been for purposes of mosquito control, although G. affinis is not considered to be any more effective against mosquitoes than most native mosquito-eating species (ISSG 2006). Gambusia affinis is a common inhabitant of lower salinity portions of the lagoon and associated upland freshwater systems. Salt marshes, mosquito impoundments, and mesohaline seagrass beds are among the habitats utilized by this species.

U.S.A. and Mexico, introduced widely elsewhere.

Dorsal spines (total): 0; Dorsal soft rays (total): 7 - 9; Analspines: 0; Analsoft rays: 9 - 10

Maximum size: 40 mm TL

4.0 cm TL (male/unsexed; (Ref. 30578)); 7 cm TL (female); max. reported age: 3 years (Ref. 796)

Length: 6 cm

Female mosquitofish reach a maximum total length of around 6-7 cm while males may reach around 4 cm (FishBase 2004, GLAVCD undated), although most individuals are somewhat smaller.The maximum age reported for the species is 3 years (FishBase 2004).

Origin of dorsal fin opposite 7th anal ray. Length of anal base much less than half distance from caudal. 8 horizontal scale rows between back and abdomen. Ventrals terminate immediately before anal fin. Pelvic fins reach ventrals.

G. holbrooki usually has seven dorsal rays and a gonopodium with prominent teeth on ray three. G. affinis usually has six dorsal rays and lacks prominent teeth on gonopodial ray three. Both subspecies have a chromosome number of 2n = 48 but female G. affinis possess a large heteromorphic sex chromosome which is lacking in G. holbrooki (Black and Howell 1979).

In Arizona, G. affinis may be confused with Poeciliopsis occidentalis, the Sonoran topminnow. In topminnows the gonopodium is asymmetrical to the left, large hooks and serrae absent on gonopodial tip, and the gonopodium reaches beyond the snout when directed forward. The pelvic fins of males are unmodified and somewhat reduced. Many breeding males will be blackened. In G. affinis the gonopodium is symmetrical with large hooks and serrae on the tip. The pelvic fins of males are modified with a fleshy appendage on the distal third of the first, short, unbranched ray. Males are rarely blackened.

As previously noted, Gambusia affinis and Gambusia holbrooki are sufficiently similar in appearance and behavior to cause considerable taxonomic difficulties, and these may or may not be distinct species. In south Florida, Gambusia affinis co-occurs with the congeneric mangrove gambusia, G. rhizophorae. The latter species is not known from as far north as the IRL however (Ray et al. 1986).The characteristic net-like scale pattern and the poster origin of the dorsal fin relative to the anal fin are typically sufficient to distinguish Gambusia from the co-occurring poeciliid, the sailfin molly, Poecilia latipinna (Hoese and Moore 1977).Poeciliid fishes can generally be differentiated from the potentially similar looking cyprinodontids (the killifishes) by the presence of either a gravid spot (mature females) or an intromittent organ (occurring on mature males) on the former.

Habitat Type: Freshwater

Comments: Habitat includes river channels, margins, backwaters; springs, marshes, and artificial habitats of all kinds (Minckley et al. 1991). Often this species occurs in shallow, often stagnant, ponds and the shallow edges of lakes and streams where predatory fishes are largely absent and temperatures are high. It is most abundant in shallow water with thick vegetation (Hubbs 1971). It also occurs in brackish sloughs and coastal saltwater habitats (Tabb and Manning 1961, Odum 1971). This fish is more tolerant of pollution than are most other fishes (Lewis 1970, Kushlan 1974). It tolerates dissolved oxygen levels as low as 0.18 mg/L (Ahuja 1964) but cannot tolerate extreme cold; temperature apparently limits the range northward (Hubbs 1971). However, some populations are known to overwinter under ice in Indiana and Illinois (Krumholz 1944).

benthopelagic; potamodromous; freshwater; brackish; pH range: 6.0 - 8.0; dH range: 5 - 19

nektonic

Depth range based on 40 specimens in 2 taxa.

Environmental ranges
  Depth range (m): 0.05 - 2

Graphical representation

Depth range (m): 0.05 - 2
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Potamodromous. Migrating within streams, migratory in rivers, e.g. Saliminus, Moxostoma, Labeo. Migrations should be cyclical and predictable and cover more than 100 km.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Comments: Opportunistic omnivore; eats mainly small invertebrates, often taken near water surface. Also eats small fishes and, in the absence of abundant animal food, algae and diatoms (Moyle 1976).

Mosquitofish are principally carnivorous, and have strong, conical teeth and short guts (Meffe et al. 1983, Turner and Snelson 1984). They are reported to feed on rotifers, snails, spiders, insect larvae, crustaceans, algae, and fish fry, including their own progeny (Barnickol 1941, Minckley 1973, Meffe and Crump 1987). Cannibalism has been documented by several authors (Seale 1917, Krumholz 1948, Walters and Legner 1980, Harrington and Harrington 1982). Plant material is taken occasionally (Barnickol 1941) and may make up a significant portion of the diet during periods of scarcity of animal prey (Harrington and Harrington 1982). Grubb (1972) showed that anuran eggs from temporary ponds were preferentially selected over those breeding in permanent systems. Several workers have documented changes in the prey community after mosquitofish introduction (Hurlbert et al. 1972, Farley and Younce 1977, Hurlbert and Mulla 1981, Walters and Legner 1980).

Due to their name, these fishes are popularly believed to be "super" mosquito-larvae predators. Reddy and Shakuntala (1979), however, found that adult females grew poorly on a diet of mosquito larvae, but they grew quickly on tubifex worms. These results matched the outcome of preference tests, i.e. worms were chosen over mosquito larvae. Cech et al. (1980) found that juveniles grew more quickly when they were raised on brine shrimp nauplii than tubifex worms. Many biologists have concluded these fishes are no more effective in mosquito-larval control than various native fishes (Cross 1967). The effectiveness of predation on mosquito larvae decreases as water volume decreases (Reddy and Pandian 1973).

Inhabits standing to slow-flowing water; most common in vegetated ponds and lakes, backwaters and quiet pools of streams (Ref. 5723). Most abundant in lower reaches of streams (Ref. 44091). Frequents brackish water. Feeds on insects, zooplankton and detritus. Used as live food for carnivorous aquarium fishes (Ref. 5723).

Mosquitofish feed primarily on zooplankton, small insects and insect larvae, and detrital material (ISSG 2006). As the common name suggests, they are voracious consumers of mosquito larvae. All sizes and ages of mosquitofish feed on mosquito larvae, and a large female mosquitofish can consume hundreds of larvae a day (GLAVCD undated). Rajasekharan and Chowdaiah (1972) demonstrated that G. affinis could discern between different species of simultaneously presented mosquito larvae and preferentially consumed certain species based on a number of factors facilitating prey capture, including size, vertical position in the water column, and the tendency of larvae to clump in groups.Baber and Babbitt (2004) indicate Gambusia () are capable of effectively consuming tadpoles of two Florida amphibians, significantly impacting prey density. In addition, G. affinis is capable of foraging effectively in densely vegetated areas that would likely provide cover from larger predatory fish.Mosquitofish, particularly where it occurs as a non-native, also prey heavily on the eggs and young of co-occurring fish species. Predators: Britton and Moser (1988) report that G. affinis represents a significant portion of the diets of four species of Camargue herons they studied. The authors also indicate that female fish are preferentially consumed over the smaller males, in apparent concordance with optimal foraging theory. Parasites: Gambusia affinis has been discovered to be one of several primarily freshwater fishes that serve as intermediate hosts of nematodes of genus Falcaustra, adults of whom typically infest reptile or amphibian hosts (Moravec et al. 1995). Habitats: Gambusia affinis occurs in a variety of freshwater and in protected brackish environments. It preferentially occupies vegetated habitats, including salt marsh and seagrass beds (Ray 1986). It is benthic and non-migratory in habit and is most often encountered in standing or slow-flowing waters (FishBase 2004, IGGS 2006).Preference experiments by Casterlin and Reynolds (1977) revealed that mosquitofish selectively occupied areas with subsurface vegetation but avoided floating cover that restricted access to the water surface. Activity Time: Lined sole are typically active in the evening hours, spending much of the daytime hours buried in shallow sand.

Rhabdochona Infestation 6. Parasitic infestations (protozoa, worms, etc.)

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300

Comments: This species is represented by a large number of occurrences (subpopulations).

>1,000,000 individuals

Comments: "Possibly the single most abundant freshwater fish in the world" (Minckley et al. 1991).

While population densities in some portions of the IRL may be limited by salinity, Minckley et al. (1991) suggest that Gambusia affinis may be "possibly the single most abundant freshwater fish in the world".

May experience severe winter mortality in some areas, but may quickly reestablish population.

Predators include water snakes (Nerodia) (Mushinsky and Hebrard 1977, Kofron 1978), water birds (Kushlan 1973), spiders (Suhr and Davis 1974), and fishes such as black basses and gars (Hunt 1953).

The species is viviparous (Ref. 5258). Internal fertilization is possible because the anal fin of the male is modified into a copulatory organ. The females carries about 30 alevins and gestation lasts for a period of 24 days (Ref. 6348) to a month (Ref. 30578).

Maximum longevity: 3 years Observations: The majority of animals die in the first year of life. Although age at sexual maturity has not been determined, it is likely less than three months. Reproductive senescence has been documented in these animals (Patnaik et al. 1994).

Fish born early in the spring may reproduce later in the summer and fall. Those born late in the reproductive season overwinter before reproducing (Krumholz 1948). In southcentral Texas, young may be collected from March to October with a peak in abundance in April (Davis 1978). In some constant temperature springs, these fish cease reproduction in winter (Brown and Fox 1966, Davis 1978). However, some populations from thermal habitats (such as cooling ponds and lakes) reproduce year-round (Ferens and Murphy 1974, Bennett and Goodyear 1978). At the Savannah River Power Plant site, South Carolina, fish reproduce throughout the winter although at much reduced brood sizes (Meffe, pers. comm., cited in Constantz 1989). These same workers found that the percentage of reproductively active females increased with increasing water temperature.

Mosquitofish have internal fertilization and are ovoviviparous (Sublette et al. 1990). Females can store sperm from one copulation and fertilize several broods sequentially (Krumholz 1948). After a gestational period of 21 to 28 days, the young are born alive at a size of approximately eight to nine mm total length (Krumholz 1948). Larger females produce more offspring (Krumholz 1948). Brood sizes of one to 315 young have been reported (Barney and Anson 1921, Moyle 1976). Females annually have four to five broods (Krumholz 1948). Sex ratios are 1:1 at birth, but in older cohorts, the number of males declines relative to the number of females (Krumholz 1948). Under optimal conditions females can become gravid at 6 weeks of age, produce 2-3 broods in first summer. Few individuals live more than 15 months (Moyle 1976).

Life history is flexible, varies with environmental conditions (Stearns 1983).

accomplished through the use of the male gonopodium. An early description of mating behavior is that of Collier (1936). The male faces forward and swings the gonopodium forward, initiating brief contact between the gonopodial tip and the oviductal opening and transferring sperm to the female.Viable sperm can be stored by females for several months, and the stored sperm in any female is likely derived from multiple matings with a variety of males (Medlen 1951).Male mosquitofish mature at approximately 1 month/21 mm SL, and females at 28 mm/6 weeks (McDowall 2000).

Females typically brood around 60 young, but large individuals may carry 300 or more (McDowall 2000).The gestation period has been experimentally determined to average around 24 days, a timeframe that is in close agreement with field observations of pond-raised animals (Krumholz 1948). Most fry in the experimental investigation had absorbed the maternal yolk before being liberated, but some broods contained animals that had not completely absorbed the yolk sacs.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 13
Specimens with Barcodes: 34
Species With Barcodes: 1

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There are 13 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

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Canada

Rounded National Status Rank: NNR - Unranked

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Global Short Term Trend: Relatively stable (=10% change)

Comments: Trend over the past 10 years or three generations is uncertain but likely relatively stable.

Global Long Term Trend: Increase of >25%

Comments: No major threats are known.

Not Evaluated

Restoration Potential: Not applicable.

Preserve Selection and Design Considerations: Lands do not need to be protected to provide adequate habitat within the native range.

Management Requirements: It is unclear whether management activities can control this fish. Eradication efforts have often been temporarily successful, but either not all individuals were killed or reintroductions were made. Certainly, eradication efforts must be followed with intensive monitoring. Preventative measures, such as barrier construction to obstruct the paths into uncolonized tributaries, should be taken when feasible. Transport and introduction of non-native fishes should be curtailed. Natural flooding regimes in western streams could aid in keeping populations in check. Meffe (1984, 1985) showed that flooding removes proportionally more mosquitofish than native topminnows.

Regulations should be drafted and/or enforced that discourage transport and stocking of non-native fishes into uncolonized habitats. An education program targeted at fishers relating the damage non-native fishes do to the environment should be implemented. An education program targeted at state and federal agencies should be implemented explaining the detrimental impact of stocking mosquitofish for mosquito larvae control. Natural barriers can be enhanced, or new barriers built to prevent the invasion of non-native fishes. Barrier design should not significantly alter stream flow and the potential impact on natural upstream and downstream movements of native fishes should be assessed. Barrier design must be approved by appropriate agencies and the appropriate Desert Fishes Recovery Teams.

Monitoring Programs: Information on mosquitofish is usually gathered incidental to other monitoring programs.

Management Research Needs: Because this is a wide ranging eastern species, much of the biology is known in the native habitat. The following specific topics are research areas that should be addressed relative to locations where introductions have been made: (1) rate of colonization in stream reaches after flooding events or after new introductions, (2) competition for food with native species, comparing diets of all life stages, (3) reproductive potential in introduced locations, emphasizing comparisons with native species, (4) aggression and predation directed towards native species in field studies, and (5) an evaluation of past eradication efforts, and (6) an analysis of sites where mosquitofish and native species have coexisted for several years (e.g. Black Draw, San Bernardino National Wildlife Refuge), and comparison to sites where mosquitofish and native species do not coexist.

fisheries: minor commercial; aquarium: commercial

Economic/Ecological Importance: Gambusia affinis is among the most widely introduced fish species worldwide, and a number of countries have reported negative environmental consequences in the wake of mosquitofish introduction (Fishbase 2004).Although effective as a mosquito control agent and widely introduced for this purpose, mosquitofish have been found to compete with or displace indigenous fish and to otherwise disrupt habitats. For example, McDowall (1990) reports that selective predation by mosquitofish can alter zooplankton, insect and crustacean communities.G. affinis has been nominated as among the 100 "World's Worst" invaders by the Invasive Species Specialist Group (ISSG 2006).

Stewardship Overview: The spread of mosquitofish outside its native range should be monitored and necessary steps taken to: (1) understand the competitive edge it has over native species, (2) limit its introduction or invasion into new locations, and (3) evaluate the possible benefit of eradication efforts in locations that can be rehabilitated for native fishes.

Species Impact: Outside their native range, mosquitofish play a role in decreasing populations of native fishes (Miller 1961, Myers 1965, Minckley and Deacon 1968). Due to the number of introductions and corresponding decreases in native fish populations, there can be no doubt of the destructive nature of such introductions. Myers (1965) wrote that almost everywhere introductions have been made, mosquitofish have gradually eliminated or reduced populations of small native fishes. For example, mosquitofish have been instrumental in eliminating native populations of Poeciliopsis occidentalis in the southwestern U.S. (Sublette et al. 1990); P. occidentalis may be effectively eliminated in 1-3 years (Meffe 1984). Evermann and Clark (1931) reported that mosquitofish in the Salton Sea, California, drove out Cyprinodon macularius less than 10 years after introduction to the state. The mechanism for many of these reductions is believed to be predation (Meffe 1985, Courtenay and Meffe 1989). Myers (1965) reported that mosquitofish have even reduced largemouth bass (Micropterus salmoides) and carp (Cyprinus carpio) populations due to predation on larvae. Another problem is caused when mosquitofish hybridize with other Gambusia species (Yardley and Hubbs 1976, Rutherford 1980). Intergradation then corrupts the genome of the native species.

Introduced mosquitofish also prey heavily on amphibian larvae (Goodsell and Kats 1999) and potentially negatively impact salamander and frog populations (Lawler et al. 1999).