Pacific Northwest Aquatic Invasive Profile:

Western ( affinis)

Laura Johnson 423 December 3, 2008

Figure 1. Western mosquitofish G. affinis (photo source: www.usgs.gov). Diagnostic information eleven short spines on ray 3 (Page and Burr 1991). : Until 1988, both the western mosquitofish (G. : affinis) and (G. holbrooki) : Gambusia were classified as subspecies of G. affinis. The Species: affinis classification of each fish as a separate species is important since they are native to different Common names: Western mosquitofish, portions of the eastern United States (Wooten et mosquitofish al. 1988). G. affinis can be distinguished from G. holbrooki by having six dorsal rays instead of The western mosquitofish, Gambusia seven, and a lack of prominent teeth on affinis, is a small (maximum 6.5 cm) gray or gonopodial ray three (Page and Burr 1991). brown fish with a rounded tail and upturned mouth (Figures 1 and 2). It may have a large Life-history and basic ecology dusky to black teardrop marking beneath its eye (as in Figure 1), but this marking is sometimes Life cycle reduced (as in Figure 2). G. affinis has a dark G. affinis are ovoviviparous, meaning stripe along its back to the , yellow and that the young develop within eggs inside the blue iridescence on transparent silver-gray body mother’s body and are then born live and do not sides, and six dorsal rays. G. affinis can be receive additional nourishment from the mother further distinguished from other members of its (Wydoski and Whitney 2003). Newborns are genus by a gonopodium with an elbow on ray 4a small, and weigh only about 1.2 to 1.3 mg. composed of two or more segments, and eight to Maturation can occur in as little as 3 to 4 weeks, although individuals born at the end of the reproductive season may delay maturity for 6 to 7 months, until the beginning of the following season. The lifespan of G. affinis differs for males and females, with females living 6 months to 1.5 years, and males averaging a much shorter lifespan, although an accurate estimate is unavailable (Haynes and Cashner 1995).

Figure 2. G. affinis in a human hand to demonstrate approximate size (photo source: www.aqua-fish.net)

Feeding habits anything but a larvae specialist (Gido G. affinis is omnivorous and utilizes a and Franssen 2007; Goodsell and Kats 1999). variety of food sources, which may give it an The predatory feeding behavior of G. affinis advantage in colonizing new sites (Lockwood et causes serious ecosystem alterations, as shown al. 2007). It is an aggressive predator and by Hurlbert et al. (1972) and Meffe (1985). commonly preys on the eggs, juveniles, and Hurlbert et al. (1972) conducted a feeding study small adults of other fish species. Like many involving G. affinis and found that it reduced predatory , they have strong, conical teeth crustaceans, insects, and rotifer populations and short guts, and they consume terrestrial and within experimental pools, which subsequently aquatic vertebrates, detritus, algae, and vascular caused an increase in phytoplankton plants (Meffe and Snelson 1989). Grubb (1972) populations. Additionally, Meffe (1985) also found that G. affinis prey heavily on anuran documented the impact of G. affinis on the amphibian eggs when they are available (Grubb population of the Sonoran topminnow 1972). Similarly, G. affinis preys heavily on the ( occidentalis), an endangered fish larvae of newts and the tadpoles of native to the southwestern United States. G. Pacific treefrogs, and may negatively affect their affinis is implicated in the local extirpation of P. populations (Goodsell and Kats 1999). G. occidentalis in its native habitat, partially due to affinis also engage in cannibalism, which may predation by G. affinis (Meffe 1985). provide growth and reproductive benefits for individuals (Meffe and Crump 1987). Reproductive strategies Although G. affinis received both its name and G. affinis displays high fecundity and reputation for its supposed predation on short gestation periods, both of which may mosquito larvae, studies have demonstrated that confer success in the biological invasion process when other food sources are available, G. affinis (Haynes and Cashner 1995; Lockwood et al. does not necessarily prefer mosquito larvae. For 2007). The reproductive season generally lasts example, Goodsell and Kats (1999) showed that about 7 months, although in warmer climates even when mosquito larvae were provided as such as Hawaii, reproduction may occur year- food for G. affinis in a controlled feeding round. In areas where reproductive seasons are experiment, they still preyed voraciously on shorter, they usually begin in spring and end in amphibian tadpoles. Furthermore, analyses of fall. The gestation period ranges from only one stomach contents of wild-caught G. affinis in to three weeks. Females may produce anywhere two separate studies revealed a variety of prey in from one to seven broods per reproductive their stomachs, proving that G. affinis is season, and each brood may contain up to about 200 . The fecundity of G. affinis is high, but ultimately depends on female size and these conditions are lethal to most freshwater reproductive status as well as geographic fish, G. affinis individuals were able to survive location. Fecundity tends to decrease from north at least a week in this environment (Hubbs to south and east to west (Haynes and Cashner 2000). 1995). In addition, female G. affinis are able to store sperm for extended periods of time, so that Biotic associations one mating may result in multiple broods (Farr The primary biotic associations of G. 1989). affinis are parasitic, and no commensal or pathogenic associations are described in the Environmental optima and tolerances literature. G. affinis individuals commonly The optimal environment of G. affinis is suffer from black spot disease, which is caused warm, shallow, slow-moving waters with dense by a parasitic trematode commonly known as a vegetation, high mineral content, and abundant black grub (Tobler and Schlupp 2008). Black food organisms. Specifically, they thrive in grubs use as an intermediate fresh and brackish water, and are found in host, between their definitive host, the belted ponds, ditches, lakes, creeks, rivers, and springs. kingfisher, and snails. Black grubs enter They are generally limited by cold temperatures, freshwater fish such as G. affinis by penetrating and cannot tolerate temperatures below 4 the skin and becoming enclosed in the fish’s degrees Celsius, which limits the distribution of tissue, where they form pinhead-sized black G. affinis in the northern United States. They spots, hence the name black spot disease (Figure are occasionally found in colder climates due to 3). The trematodes can greatly harm the host annual stocking, but they are not able to fish, but they cannot spread from fish to fish. establish a self-sustaining population. However, The penetration of the parasites into the skin can they can tolerate water temperatures up to 38 cause mechanical damage and hemorrhage of degrees Celsius and thrive in warm climates the host fish, as well as lipid depletion, which (Wydoski and Whitney 2003). can lead to death (Lane and Morris 2000). Hubbs (2000) demonstrated the ability of G. Tobler and Schlupp (2008) observed a decrease affinis to thrive in both high and low in shoaling behavior among G. affinis with black environmental quality environments. During a spot disease. They hypothesized that individuals drought in west Texas in 1988, the Diamond/Y with different markings (black spots) caused Draw drainage experienced extremely poor increased detection and subsequent predation of environmental quality of 41 ppt salinity, total healthy individuals. Additionally, black spot ammonia over 10 ppm, nitrates over 100 ppm, disease is associated with increased energy and dissolved oxygen below 1 ppm. Although demands due to lipid loss, and shoaling with sp., although the effect of this parasite on natural populations of G. affinis is not known (Crandall and Bowser 1981).

Current geographic distribution

G. affinis has established populations in many states outside of its native range, which is

Figure 3. A fish (bass) exhibiting black spot disease located in the southeastern United States (Figure (photo source: Fisheries Division, Michigan Dept. of 4). G. affinis exists throughout the Pacific Natural Resources). Northwest, mostly along river corridors such as the Columbia, Willamette, Snake, Klamath, individuals requiring extra resources may reduce Clark Fork, and Flathead (Figure 5). In food available to other group members. As a Washington State, biologists found G. affinis result, healthy G. affinis preferred to shoal with overwintering in ponds near the confluence of other healthy individuals and excluded those the Snake and Columbia Rivers in the 1970s, with black spot disease (Tobler and Schlupp and it has since spread into other portions of the 2008). Columbia River. In the 1990s, they were Tapeworms may also infect G. affinis, which captured in the John Day River, Lewis River, serve as the definitive host for the tapeworm and Yakima River. Generally, they inhabit Bothriocephalus acheilognathi. Granath and slow-moving backwaters and sloughs in the Esch (1983) found that infection with B. mid- to lower Columbia River and the lower acheilognathi caused decreased survival in G. reaches of the Columbia’s tributaries. However, affinis. Increasing temperatures reduced since they are widely distributed for mosquito survival in infected fish, as higher temperatures control in private ponds, they may occur in caused increased growth of the tapeworm almost any water body in the Pacific Northwest (Granath and Esch 1983). (Wydoski and Whitney 2003). Scientists have found G. affinis populations infected with the microsporidian parasitic History of Invasiveness Glugea sp. in California. Glugea sp. can occupy the majority of the abdominal cavity of G. affinis Due to its reputation for biological with cyst-like structures and cause decreased control of mosquitoes, G. affinis has a long swimming ability. Mortality may also occur invasion history and has been stocked when G. affinis is heavily infected with Glugea throughout most of the United States and the rest Figure 4. The current distribution of G. affinis in the United States. Note that the various shades of pink and red represent hydrologic units where G. affinis occur (color difference indicates scale of information, not population density). Light beige represents areas with no known populations of G. affinis, while darker brown indicates its native range (source: USGS Nonindigenous Aquatic Species program, nas.er.usgs.gov).

were generally unknown or undocumented; thus, both species are widely distributed around the world (Fuller et al. 1999). In 1901, the entomologist Leland Ossian Howard advocated for the use of Gambusia sp. in after he obtained information about its feeding habits. Several years later, in 1905, Gambusia sp. individuals were transported from North Carolina to Figure 5. The current distribution of G. affinis in the Camden, New Jersey and released. This is the Pacific Northwest. Color-coding is the same as in Figure 3 first known introduction of Gambusia sp. (source: USGS Nonindigenous Aquatic Species program, outside its native range. Several years later, the nas.er.usgs.gov). mosquitofish was transported to Hawaii and the of the world. It is important to note that most of Philippines and released for mosquito control, the introductions of the mosquitofish took place and populations successfully established in each prior to the distinction of G. affinis and G. location. In the 1920s, Gambusia sp. were holbrooki, and the origins of introduced stocks introduced into Europe, and shortly thereafter to Asia and Africa (Krumholz 1948). Now, these populations have displayed the ability to mosquitofish have established self-sustaining spread from the locations of initial stocking populations on every continent in the world, (Fuller et al. 1999; Rehage and Sih 2004). G. except Antarctica (Courtenay and Meffe 1989). affinis display nearly all of the characteristics commonly associated with successful invasive Invasion process species, as identified by Lockwood et al. (2007): abundant and widely distributed in their native Pathways, vectors, and routes of introduction range, broad environmental tolerances, short The primary pathway of introduction of generation times, high fecundity, rapid growth, G. affinis is stocking for biocontrol. Both early sexual maturity, broad diet, and association citizens and government agencies routinely with human activities. Most likely, all of these stock G. affinis for predation on mosquito larvae traits influence the successful establishment and (Fuller et al. 1999). In many states, fish and spread of G. affinis outside its native range. wildlife departments conduct annual stocking of Furthermore, G. affinis has demonstrated an G. affinis (Schleier et al. 2007; Fuller et al. ability to live in disturbed, degraded habitats 1999). Additionally, state and local health such as retention ponds and dammed, departments appear to view G. affinis as an channelized, and diverted rivers (Courtenay and attractive alternative to pesticides, and Meffe 1989). The ability of G. affinis to survive encourage citizens to stock western mosquitofish in environmental conditions that are lethal to in backyard ponds and water features (Fuller et most other freshwater fish may also confer a al. 1999). Due to the widespread distribution of competitive advantage and allow the species to G. affinis and stocking activities conducted by withstand environmental events that eradicate both government agencies and private other species in a given location (Hubbs 2000). individuals, vectors and routes associated with Thus, as human activity degrades habitats, an the intentional introduction of G. affinis are ecological niche becomes available which G. probably numerous but remain unidentified in affinis appear to be more adept at filling than are the literature. Some introductions of G. affinis native fish (Courtenay and Meffe 1989). are probably escapees from stocking locations, Rehage and Sih (2004) conducted an experiment in flood events or other natural disasters to test the dispersal behavior of four species of (Courtenay and Meffe 1989). Gambusia, and hypothesized that species with greater invasion success such as G. affinis would Factors influencing establishment and spread display greater dispersal tendencies than G. affinis has commonly established Gambusia species that were not successful self-sustaining populations where stocked, and invaders (such as G. geiseri). As expected, G. affinis were more likely to disperse out of Potential ecological and/or economic impacts experimental introductory pools, and According to Courtenay and Meffe subsequently dispersed faster and covered (1989), G. affinis and G. holbrooki have had the greater distances than did non-invasive greatest ecological impacts of all of the poeciliid Gambusia species (Rehage and Sih 2004). The (live-bearing) fish. The primary ecological bold dispersal tendencies exhibited by G. affinis impact is predation on larvae, juveniles, or small in experimental introductory pools are probably adults of other fish species, and such predation displayed in wild populations, and assist with has locally extirpated native fish in some regions the successful spread of introduced populations. (Courtenay and Meffe 1989; Meffe 1985). The largest limitation to the establishment and Additionally, they have substantial effects on spread of G. affinis is its intolerance to waters native amphibian populations due to predation below 4 degrees Celsius. In cold climates, it on eggs and tadpoles (Grubb 1972; Goodsell and lacks the ability to overwinter and where stocked Kats 1999). Adult G. affinis are extremely in cold climates, it must be restocked annually aggressive towards other fish, even fish larger (Wydoski and Whitney 2003). Due to its water than they are. They may attack these fish, temperature requirements, G. affinis has spread killing them or injuring them enough to cause throughout temperate and tropical regions of the eventual death (Courtenay and Meffe 1989). world but has failed to spread in colder regions Potentially, G. affinis may continue to cause (Fuller et al. 1999). local extirpation of native fish and amphibians, Additional limitations to G. affinis populations or even cause of some are heavy flooding, springhead conditions, and species that are already endangered (Meffe natural predators. Flash flooding in the 1985). Additional negative ecological impacts southwest United States has reduced or include hybridization with native species and destroyed populations of G. affinis, while native introduction of parasites, but both of these fish are able to withstand the high flow potential impacts of G. affinis have not been conditions. Springhead waters in the southwest thoroughly investigated (Courtenay and Meffe United States have low pH and high dissolved 1989).

CO2, and have served as a refugia for native fish G. affinis may also be responsible for ecosystem when threatened with invasion by G. affinis. level impacts. In one study, G. affinis Finally, predation by fish and aquatic birds may introduction caused large phytoplankton blooms, limit populations of G. affinis (Courtenay and decreased water clarity, and higher water

Meffe 1989). temperatures (Hurlbert et al. 1972). Another study found that experimental ponds containing G. affinis had higher pH and oxygen levels than those without (Hurlbert and Mulla 1981). plan that applies to both G. holbrooki and G. Alteration of the ecosystem due to G. affinis affinis. Both G. holbrooki and G. affinis are invasion may have far-reaching impacts. invasive in Australia, and have had detrimental Although the literature has not explicitly stated effects on native fish populations there. Their the economic impact of G. affinis, it is management plan details chemical, biological, implicated in the reduction of populations of and physical methods that may be used to due to predation on eggs, control Gambusia. Chemical methods include larvae, and juveniles (Meffe 1985). Presumably, creation of Gambusia-free environments with if G. affinis is able to cause a substantial decline the non-specific chemical rotenone prior to in the populations of popular sportfish, stocking with native fish and amphibians. economic impacts will be evident. However, due to the non-specific nature of rotenone, the New South Wales National Parks Management strategies and control methods and Wildlife Service prefers biological and physical control methods over chemical ones. Very few management strategies and The favored biological control method is control methods are in place for G. affinis in the predation on Gambusia by larger species. The United States, since many government agencies use of parasites, pathogens, bacteria and viruses view the fish as beneficial in reducing mosquito to control Gambusia are also an option, but have populations, despite the fact that studies have not been researched thoroughly at this time. The shown otherwise. Typically, management preferred physical control method is the draining consists of a permitting process in which citizens and drying of particular habitats critical to native desiring G. affinis for backyard ponds must state species followed by reduction of water levels to that they will not release individuals into prevent Gambusia from re-entering the connected waterways. Although scientists and waterbodies. Finally, the New South Wales agencies recognize G. affinis as a highly National Parks and Wildlife Service invasive species and many studies show its recommends restoring degraded habitats to their detrimental impacts on other species, original state, since Gambusia thrive in governments continue to stock them outside disturbed, degraded habitats. Restoration of their native range for biocontrol of mosquitoes, degraded habitats may give native species a and allow citizens to follow suit on private long-term competitive advantage over Gambusia property (Courtenay and Meffe 1989). (New South Wales National Parks and Wildlife Although not local, the National Parks Service 2003). and Wildlife Service of New South Wales, Australia, has created a detailed management Literature Cited Goodsell JA, L Kats B (1999) Effect of introduced mosquitofish on Pacific Courtenay WR Jr, Meffe GK (1989) Small treefrogs and the role of alternative prey. fishes in strange places: a review of Conserv Biol 13:921-924 introduced poeciliids. In: Meffe GK, Snelson FF Jr (eds) Ecology and evolution Granath WO Jr, GW Esch (1983) Survivorship of livebearing fishes (Poeciliidae). Prentice and parasite-induced host mortality among Hall, Englewood Cliffs, pp 319-331 mosquitofish in a predator-free, North Carolina cooling reservoir. Amer Midland Crandall TA, PR Bowser (1981) A Nat 110:314-323 microsporidian infection in a natural population of mosquitofish Gambusia Grubb JC (1972) Differential predation by affinis. J Fish Diseases 4:317-324 Gambusia affinis on the eggs of seven species of anuran amphibians. Amer Farr JA (1989) Sexual selection and secondary Midland Nat 88:102-108 sexual differentiation in poeciliids: determinants of male mating success and Haynes JL, RC Cashner (1995) Life history and the evolution of female choice. In: Meffe population dynamics of the western GK, Snelson FF Jr (eds) Ecology and mosquitofish: a comparison of natural and evolution of livebearing fishes introduced populations. J Fish Biol (Poeciliidae). Prentice Hall, Englewood 46:1026-1041 Cliffs, pp 89-123 Hubbs C (2000) Survival of Gambusia affinis in Fuller PL, LG Nico, JD Williams (1999) a hostile environment. Southwest Nat Nonindigenous fishes introduced into 45:521-522 inland waters of the United States. American Fisheries Society, Spec. Pub. 27, Hurlbert SH, MS Mulla (1981) Impacts of Bethesda, MD mosquitofish (Gambusia affinis) predation on plankton communities. Hydrobiologia Gido KB, NR Franssen (2007) Invasion of 83:125-151 stream fishes into low trophic positions. Hurlbert SH, J Zedler, D Fairbanks (1972) Ecol Freshwater Fishes 16:457-464 Ecosystem alteration by mosquitofish (Gambusia affinis) predation. Science 175:639-641

Krumholz LA (1948) Reproduction in the Page LM, BM Burr (1991) A field guide to western mosquitofish, Gambusia affinis freshwater fishes: North America north of (Baird & Girard), and its use in mosquito Mexico. Houghton Mifflin Company, control. Ecol Monogr 18:1-43 Boston

Lane RL, JE Morris (2000) Biology, prevention, Rehage JS, A Sih (2004) Dispersal behavior, and effects of common grubs (Digenetic boldness and the link to invasiveness: a trematodes) in freshwater fish. USDA comparison of four Gambusia species. Biol Technical Bulletin Series No. 115 Inv 6:379-391

Lockwood JL, MF Hoopes, MP Marchetti Schleier JJ, SE Sing, RKD Peterson (2007) (2007) Invasion ecology. Blackwell Regional ecological risk assessment for the Publishing introduction of Gambusia affinis (western mosquitofish) into Montana watersheds. Meffe GK (1985) Predation and species Biol Inv 10:1277-1287 replacement in American southwestern fishes: a case study. Southwest Nat 30:173- Tobler M, I Schlupp (2008) Influence of black 187 spot disease on shoaling behaviour in female western mosquitofish, Gambusia Meffe GK, ML Crump (1987) Possible growth affinis (Poeciliidae, Teleostei). Envr Biol and reproductive benefits of cannibalism in Fish 81:29-34 the mosquitofish. Amer Nat 129:203-212 Wooten MC, KT Scribner, MH Smith (1988) Meffe GK, FF Snelson (1989) An ecological Genetic variability and systematics of overview of poeciliid fishes. In: Meffe GK, Gambusia in the Southeastern United Snelson FF Jr (eds) Ecology and evolution States. Copeia 1988:283-289 of livebearing fishes (Poeciliidae). Prentice Hall, Englewood Cliffs, pp 89-123 Wydoski RS, RL Whitney (2003) Inland fishes of Washington. University of Washington New South Wales National Parks and Wildlife Press, Seattle Service (2003) Approved NSW threat abatement plan: predation by Gambusia holbrooki – the plague minnow. Other key sources of information and Phone: 360-7539508 bibliographies Email: [email protected]

United States Geological Survey Mosquitofish Allen Pleus Information: Aquatic Nuisance Species Coordinator http://nas.er.usgs.gov/queries/FactSheet.asp?spe Washington Department of Fish and Wildlife ciesID=846 Phone: 360-902-2724 Email: [email protected] Gambusia Control Homepage: http://www.gambusia.net/ Pam Meacham Assistant Aquatic Nuisance Species Coordinator Fishbase species information page for Gambusia Washington Department of Fish and Wildlife affinis: Phone: 360-902-2741 http://www.fishbase.org/Summary/speciesSumm Email: [email protected] ary.php?ID=3215&genusname=Gambusia&spec iesname=affinis Current research and management efforts

NatureServe Gambusia affinis information page: 1. University of California Davis: http://www.natureserve.org/explorer/servlet/Nat The UC Mosquito Research Program ureServe?searchName=Gambusia%20affinis investigates options for controlling mosquito populations using native fish rather than G. Michigan Department of Natural Resources affinis. technical report describing alternatives to Gambusia for mosquito control: Contact: Gregory Lanzaro, Ph.D., http://www.michigandnr.com/PUBLICATIONS/ [email protected] PDFS/ifr/ifrlibra/technical/reports/2003-2tr.pdf 2. University of California Riverside: Expert contact information in the Pacific Dr. William E. Walton at UC Riverside Northwest specializes in mosquito biology and ecology, Kevin Aitkin including control methods involving native fish Fish Biologist instead of G. affinis. Invasive Species Lead Western Washington Office Contact: William E. Walton, Ph.D., U.S. Fish and Wildlife Service [email protected]

3. Edith Cowan University, Centre for Ecosystem Management, Western Australia: Dr. Mark Lund conducts wetlands research, including the effect of G. holbrooki on Western Australian wetlands.

Contact: Dr. Mark Lund, [email protected]