The dusky millions fish, speckled mosquitofish or the one-spot livebearer (Phalloceros caudimaculatus) is a species of fish native eastern and southern Brazil, northern Argentina, Uruguay and Paraguay.[2] It has also been introduced to Australia, Malawi and New Zealand; primarily for mosquito control, but also as escapees from the aquarium trade.[2] It has been reported as having adverse ecological effects in areas where it has been introduced.[2] The females of this species grow to a total length of 6 centimetres (2.4 in), while males remain smaller.[2]

Dusky millions fish
Wild phenotype of the fish
The species' wild colors
"Speckled Kaudi" morph in aquarium
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cyprinodontiformes
Family: Poeciliidae
Genus: Phalloceros
Species:
P. caudimaculatus
Binomial name
Phalloceros caudimaculatus
(R. F. Hensel, 1868)
Synonyms[2]

Girardinus caudimaculatus Hensel, 1868

Origins

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This species originated in South America.[3] It is mainly a freshwater fish and thrives best in areas with weak water flow.[3] However, it is extremely adaptable and can thrive in a multitude of altered environments.[3] For example, although it prefers temperatures between 16 and 22 °C (61–72 °F), it can survive up to 30 °C (86 °F)[4] and down to 5 °C (41 °F).[3] The species also has a high fecundity.[5]

The dusky millions fish was one of the first species in its family, the Poeciliidae to be bred for aquarium usage.[3] Ecologists also attempted to use the fish as a mosquito control; however, the mosquito fish's diverse diet affected its efficacy as a control species.[3] The mosquito fish can eat a range of different organisms, including algae.[3]

Role as an invasive species

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The dusky millions fish was introduced to a variety of ecosystems both by aquarium keepers and as mosquito pest control.[3] The NSW area of Australia has been affected the most by its presence.[3] It reproduces and spreads well in the winter when there is a larger flow of water.[3] Australian ecologists have tried to contain this spread by killing them with rotenone; however, the infestation persists.[3] This species is most likely to be found in shallow areas with varying levels of vegetation, such as local ponds.[5]

The ecological impact of the dusky millions fish in Australia is pronounced. Its diet has affected populations of both native and non-native fish.[5] An example would be the non-native species Gambusia holbrooki.[5] It has similar features as the dusky millions fish, such as a high reproductive rate and use for mosquito control.[5] However, its population in Australia has diminished since the introduction of the dusky millions fish.[5] Furthermore, this dusky millions fish has also affected the food chain, as they have become prey for native bird species.[5]

References

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  1. ^ Salvador, G.N. (2023). "Phalloceros caudimaculatus". IUCN Red List of Threatened Species. 2023: e.T186909A1820204. doi:10.2305/IUCN.UK.2023-1.RLTS.T186909A1820204.en. Retrieved 11 February 2025.
  2. ^ a b c d e Froese, Rainer; Pauly, Daniel (eds.). "Phalloceros caudimaculatus". FishBase. November 2015 version.
  3. ^ a b c d e f g h i j k Maddern, M.G. (2008). "Distribution and spread of the introduced One-spot Livebearer Phalloceros caudimaculatus (Pisces: Poeciliidae) in southwestern Australia" (PDF). Journal of the Royal Society of Western Australia. 91: 229–235. Retrieved November 23, 2015.
  4. ^ "Phalloceros caudimaculatus". SeriouslyFish. Retrieved 21 March 2017.
  5. ^ a b c d e f g Rowley, J. J. L.; Rayner, T. S.; Pyke, G. H. (2005-09-01). "New records and invasive potential of the poeciliid fish Phalloceros caudimaculatus". New Zealand Journal of Marine and Freshwater Research. 39 (5): 1013–1022. Bibcode:2005NZJMF..39.1013R. doi:10.1080/00288330.2005.9517372. ISSN 0028-8330.