Eastern mosquitofish, mosquito fish, mosquitofish, gambusino

Type Description

"They are small fish ranging in size from 1-6 cm (Turner, 1941). Their bodies are covered with large scales. Their eyes are relatively large compared to their bodies, and their mouths are positioned upward.

These fish exhibit sexual dimorphism, with males being smaller than females and easily distinguishable from females by their gonopodium structures."

Habitat

"Gambusia holbrooki's natural habitat is the ponds, lakes, and streams of South America (Casterlin and Reynolds, 1977). These species can particularly benefit from flooded areas and floodplains (Ross and Baker, 1983). Gambusia holbrooki prefers coastal environments, waters with dense vegetation nearby, and flowing waters with stagnant waters (Lloyd, 1987).

Other habitat preferences include shallow waters, dark-colored substrates, and submersed vegetation (Casterlin and Reynolds, 1977; Arthington and Marshall, 1999). They can adapt to various aquatic environments, living in freshwater as well as brackish water, inland, coastal, and river waters.

This species seems to have difficulty adapting to rapidly flowing waters, which may hinder their ability to develop large populations (Lloyd, 1987).

The species exhibits extremely high tolerance to different physicochemical characteristics. They can live in a wide temperature range of 4-42°C (Pyke, 2005). Although they prefer living in freshwater, they have been observed to establish populations in a water source with a salinity of ‰23 (Alcaraz and Garcia-Berthou, 2007). Their distribution range worldwide is very wide. They are abundant in their natural range. A species among the 45 species found in the Poeciliidae family of the Cyprinodontiformes order (Toothed carps), Gambusia holbrooki's local distribution area is North America (Lloyd and Tomasov, 1985).

These fish are reported to have been first brought to Turkey by the French from European countries for biological control of mosquitoes, and introduced into Lake Amik (Geldiay and Balık, 1996). It is known that they have been introduced to all continents except Antarctica.

The provinces in Turkey where the species has been recorded are Adana, Afyon, Ankara, Antalya, Balıkesir, Burdur, Bursa, Denizli, Diyarbakır, Düzce, Edirne, Eskişehir, Gaziantep, Hatay, Isparta, İzmir, Kırklareli, Konya, Manisa, Mersin, Muğla, Osmaniye, Sakarya, Samsun, and Uşak."

Reproductive Information

This species has a high reproductive potential and a relatively long lifespan. It grows rapidly and reproduces frequently throughout the year. It is viviparous, meaning it gives birth to live offspring instead of laying eggs. While the optimum breeding temperature is reported to be 25°C (Geldiay and Balık, 1996), mosquito fish can start breeding at water temperatures as low as 12°C. They prefer gravel habitats for breeding.

Lifecycle

If conditions are suitable, females give birth every 3-4 weeks. Females under one year of age may have an average of 30 embryos, while those over one year old may have an average of 70 embryos (Öztürk and İkiz, 2004). In a study conducted in Acıgöl springs in Turkey, it was found that females could produce 130 embryos (Yoğurtçuoğlu and Ekmekçi, 2017).

Nutrition Information

"Gambusia species generally have a wide range of food sources (Yoğurtçuoğlu and Ekmekçi, 2017; Ergüden, 2013). These species, which consume small insects, zooplankton, and zoobenthos, can also feed on the eggs and larvae of other species with which they share the ecosystem (Goodsell and Kats 1999; Özuluğ et al., 2013; Yoğurtçuoğlu and Ekmekçi, 2017).

There are some studies on the feeding regime of Gambusia species worldwide. Sokolov and Chvaliova (1936) found that G. affinis in Turkmenistan consumed anophel, Cladocera, Coleoptera, Rotatoria, and Chironomidae; Arthington (1989) reported that G. holbrooki consumed various invertebrates, especially terrestrial and aquatic insects; Garcia-Berthou (1999) found that G. holbrooki mainly consumed insects and Crustacea, and only a small amount of mosquito larvae; Gkenas et al. (2012) stated that in Greece, G. holbrooki consumed Crustacea, Diptera, Coleptera, Hymenoptera, and Hemiptera.

In Turkey, studies on the feeding habits are limited. In a study conducted in Seyhan Dam Lake, it was found that G. holbrooki consumed 53.90% Diptera (larvae and pupae), 14.70% fish eggs, 13.72% zooplankton (Cladocera, Copepoda), 3.92% individuals of their own species (cannibalism), and 1% other insect groups (Coleoptera, Hemiptera, Hymenoptera, Trichoptera, Plecoptera) (Ergüden, 2013). Another study on the feeding ecology of G. holbrooki in freshwater sources feeding Acıgöl (Afyon/Denizli) revealed that this species exhibited significantly different feeding characteristics in different habitat conditions; while it showed herbivorous levels trophically in some habitats, it showed carnivorous characteristics in others (Yoğurtçuoğlu and Ekmekçi, 2017)."

General Impact Information

"Their highly invasive nature has been proven outside their natural distribution range. They are a highly mobile species and behave aggressively towards other species. They compete with other species they share habitats with for food and space (they are always in competition with local species) and create negative effects on local species (Kurtul and Sarı, 2017). They threaten natural biological diversity and pose a threat and loss to native species.

They have high genetic variability and are among the top 100 most invasive species in the world due to their survival success even in the worst water conditions and the many negative effects they create in the ecosystems they enter (ISSG, 2013). The most negative impact these fish have is their frequent consumption of the eggs and larvae of other fish (Goodsell and Kats, 1999). Their entry into habitats where endemic species are found poses a problem for the continuity of endemic species.

They can create ecosystem and habitat changes in the environments they enter. These species also consume zooplankton. Therefore, especially during spring and summer when they actively feed due to increasing temperatures, they can consume zooplankton excessively, leading to an increase in phytoplankton (Pyke, 2008).

This species is listed on the black list of the IUCN Global Invasive Species Database."

General Management Information

"It is known that Gambusia holbrooki can thrive even in habitats where many exotic fish are extremely sensitive to environmental pollution. Therefore, controlling the species is quite difficult and costly. The presence and abundance of Gambusia species are monitored as part of official river and stream health monitoring programs in Australia (Kennard et al., 2005). While there have been various studies on controlling the species, there is no integrated management program example to control these species.

Populations of Gambusia species can be controlled to some extent by draining small-volume water bodies and cutting off re-colonization routes. However, G. holbrooki is highly invasive and can move in water as shallow as half its body depth. To prevent the local spread of Gambusia, dispersal routes as shallow as 3 mm should be closed (e.g., ditches and channels) (Alemadi and Jenkins, 2007).

In some countries (e.g., Australia), the transportation of Gambusia by humans is prohibited. When Gambusia holbrooki is collected as waste in research programs, it should be disposed of immediately and should never be transported to another water body or taken to domestic aquariums.

There are factors that limit natural Gambusia populations; these are endemic parasites, pathogens, and predators (Courtenay and Meffe, 1989). Gambusia is reported to serve as a host for at least 23 parasite species (Arthington and Lloyd, 1989), however, most of these parasites are not host-specific. Pathogens may contribute to the suppression of Gambusia, but there is limited reliable data on their roles.

The control of the species' population is being attempted using other species. Species such as Galaxias maculatus can be introduced into small water bodies to remove Gambusia from the environment. However, after 2-4 years, the numbers of these species will decrease, leaving Gambusia the opportunity to re-establish their populations. To sustain the mortality of Gambusia species, these species need to be repeatedly released into the water.

Various attempts have been made to reduce the abundance of G. holbrooki in water bodies using rotenone. However, the tolerance shown by this species to the toxic substance used is higher than that of other local fish species."

General Pathway Information

The entry routes of Gambusia holbrooki into Turkey include biological control, floods and natural disasters, fisheries, and aquarium fishery.

Notes

The species is distributed throughout almost all of Turkey's water resources. Especially due to competition for food and habitat, its presence poses a risk to endemic species (especially toothcarps) sharing the same microhabitat.

References