Tilapia as exotic species

A number of tilapiine cichlids that are native to Africa and the Levant have been widely introduced into tropical fresh and brackish waters around the world. In some cases, the introductions were deliberate, for example to control invasive aquatic plants, as in the U.S. states of Florida and Texas. cite web | title=Florida's Exotic Freshwater Fishes | publisher=State of Florida | date = 2006 | url=http://floridafisheries.com/Fishes/non-native.html#tilapia | accessdate = 2007-02-10] Across much of Asia and Africa they have been introduced into ponds and waterways for the purposes of aquaculture. cite web | last=Nand Lal | first=Satya | coauthors=Roberto Foscarini | title=Introduction of tilapia species and constraints to tilapia farming in Fiji | publisher=Food and Agriculture Organization of the United Nations | url=http://www.fao.org/docrep/field/003/ac295e/ac295e00.htm | accessdate=2007-02-10] In other cases, unwanted fish have been released by aquarists or ornamental fish farmers into the wild.cite web | last=University of Southern Mississippi/College of Marine Sciences/Gulf Coast Research Laboratory | title=Fact Sheet for Tilapia zilli (Gervais, 1848) | publisher=Gulf States Marine Fisheries Commission | date=2005-08-03 | url=http://nis.gsmfc.org/nis_factsheet2.php?toc_id=200 | accessdate = 2007-02-10 ] cite web | last=Fuller | first=Pam L. | coauthors=Leo G. Nico | title=Nonindigenous Fishes of Florida - With a Focus on South Florida | publisher=U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology | date=2002-10-11 | url=http://sofia.usgs.gov/sfrsf/rooms/species/invasive/focus/ | accessdate=2007-02-10 ]

Because tilapiine cichlids are generally large, fast growing, breed rapidly, and tolerate a wide variety of water conditions (even marine conditions), once introduced into a habitat they generally establish themselves very quickly. In doing so they compete with native fish fauna, create turbidity in the water (by digging) thus reducing the light available for aquatic plants, and eating certain types of aquatic plants causing changes in local aquatic flora. Such problems have been observed in many different places, including Australia, Philippines, and the United States.cite web | author = Sena De Silva "et al"| title =Tilapias as Alien Aquatics in Asia and the Pacific:A Review, FAO Fisheries Technical Paper 453 | date =2004 | url=http://www.fao.org/docrep/007/y5728e/y5728e05.htm#bm5.5 | accessdate=2007-04-02 ] cite web | last=Nico | first=Leo | title =Tilapia mariae | publisher=USGS Nonindigenous Aquatic Species Database | date =2006-04-22 | url=http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=482 | accessdate=2007-02-10 ] cite web | title=Tilapia - NSW DPI - Fisheries | publisher=NSW Department of Primary Industries: Fisheries | url=http://web.archive.org/web/20060918074253/http://www.fisheries.nsw.gov.au/threatened_species/general/content/fn_tilapia.htm | accessdate=2007-02-10 ]

ingapore

In Singapore, "Oreochromis mossambicus" was introduced from Java by the Japanese during World War II, hence its local names, Japanese fish and Java fish. It was formerly very abundant in fresh and brackish waters and in the sea off the north coast. However, since the late 1980s, feral tilapiine cichlid populations in most locations have crashed, possibly due to cross breeding with more recently introduced tilapiine cichlid hybrids (red tilapia "O. mossambicus" x "O. niloticus", possibly also "O. honorum" and "O. aureus"). The offspring of the crosses may be strongly sex skewed in favor of males, and inter-species crosses tend to produce fewer fry per brood than single species spawns, thus causing the population to decline, and hybrids with "O. niloticus" may inherit the lower salinity tolerance of that species, thus restricting the habitats where these tilapiine cichlids are found.

United States

Salton Sea in Southern California is home to a large population of "Oreochromis mossambicus" known locally as Salton Sea tilapia. How they got into the Salton Sea is not known for certain.cite web | last= Horvitz | first= Steve | title =Salton Sea 101| publisher=Salton Sea Authority | date =2000 | url=http://www.saltonsea.ca.gov/ss101.htm#How%20Many%20Fish| accessdate=2007-04-02 ] The Salton Sea tilapia feed on plant material, phytoplankton (particularly diatoms), copepods, rotifers, barnacle larvae, and small annelid worms. [Riedel, Ralf; Costa-Pierce, Barry A. (2005-04) "Feeding Ecology of Salton Sea Tilapia (Oreochromis spp.)", "Bulletin, Southern California Academy of Sciences", Vol 104, Isssue 1. pp 26-36] One peculiarity of the Salton Sea are the periodic algal blooms that cause the fish, including the Salton Sea tilapia, to die in massive numbers, causing a particularly nasty smell.cite web | last= Horvitz | first= Steve | title =Salton Sea 101| publisher=Salton Sea Authority | date =2000 | url=http://www.saltonsea.ca.gov/ss101.htm#The%20Smell| accessdate=2007-04-02 ] There are also populations of tilapia in several lakes in Texas; one in Fairfield lake, another in Martin Creek lake, as well as in Lake Conroe and Stubblefield Lake.

Australia

Shortly after their first importations to Australia in the 1970s aquarium trade, tilapia were introduced into the warm waters of North Queensland dams for weed and mosquito control. cite web | last=McCutcheon | first=Peter | title =Tilapia spreads in nth Qld | publisher=Australian Broadcasting Corporation | date =2005-01-01 | url=http://www.abc.net.au/7.30/content/2005/s1305418.htm | accessdate=2007-03-01 ] Later genetic studies indicated that at least two separate introductions to the native creeks and rivers occurred.cite web | last=Mather | first=P.B. | coauthors=A.H. Arthington | title= An assessment of genetic differentiation among feral Australian tilapia populations | publisher=Australian Journal of Marine and Freshwater Research | url=http://www.publish.csiro.au/paper/MF9910721.htm | accessdate=2007-03-01 ] As early as 1979, there were established populations of "Tilapia mariae" and "Cichlasoma nigrofasciatum" in the cooler climate of Victoria, in a pond warmed by a power station cite web | last=Cadwallader | first=P.L. | coauthors=G.N. Backhouse and R. Fallu | title=Occurrence of exotic tropical fish in the cooling pondage of a power station in temperate south-eastern Australia | publisher=Australian Journal of Marine and Freshwater Research | date=1980-01-01 | url=http://www.publish.csiro.au/paper/MF9800541.htm | accessdate=2007-03-01 ] . In 1981 they were also noted to be present in the waters of Carnarvon, Western Australia cite web | title=Aquatic Invaders - Introduced species are a threat to our aquatic biodiversity: Tilapia or Mozambique Mouthbrooder | publisher=Department of Fisheries, Government of Western Australia | date=2006-06-01 | url=http://www.fish.wa.gov.au/docs/pub/IMPFreshwater/IMPFreshwaterPage05.php?0506 | accessdate=2007-03-01 ] .

Ten years later it was noted that there were established feral populations of tilapia throughout the waters of Queensland and Western Australia, and their geographical range was continuing to increase cite web | | last=Mather | first=P.B. | coauthors=A.H. Arthington | title=An assessment of genetic differentiation among feral Australian tilapia populations | publisher=Australian Journal of Marine and Freshwater Research ] . By 1991 the waters surrounding the Queensland cities of Brisbane, Townsville, and the Gascoyne River in Western Australia were filled with "Oreochromis mossambicus". It was also found that "Tilapia mariae" was a much less commonly found exotic, though its trapping in rivers north of Cairns indicated that at the time it was possibly extending its range into its preferred water temperature ranges, and that it had a great capacity for tolerating a wide range of salinity levels.

Noxious pest

Impacts on Australian rivers, creeks and ponds have been great, particularly the dramatic decreases in native fish populations due to predation and competition for food by the fast breeding tilapia that consume a vast range of food sources cite web | last=McDonald | first=Ian | title =Press Release - Tilapia under attack | publisher=Ian McDonald Federal Minister for Fisheries and Conservation at the time | date =2005-07-21 | url=http://www.mffc.gov.au/releases/2005/05141m.html | accessdate=2007-03-01 ] . Further habitat impacts include increases in local turbidity levels from nesting behaviours. Native fish, invertebrates, and other organisms also experience reduced access to cover through the aggressive territorial defence of breeding and feeding sites by some tilapia species.

Tilapia are listed as a noxious pest in Queensland, Australia, ["Exotic pest fish - commonly asked questions and answers." [http://www2.dpi.qld.gov.au/fishweb/1553.html] ] and are spreading rapidly into previously untouched and relatively pristine river systems such as the Endeavour River near Cooktown and the Eureka Creek, a tributary to the Walsh, which runs into the Mitchell. [http://www.bigpond.com/news/technology/content/20081010/2387281.asp] ["Tilapia shock: Noxious fish placed in the Endeavour River deliberately." Sarah Martin. "Cooktown Local News." January 9, 2008, p. 1.] ["Double dose of poison fails to wipe out tilapia." Sarah Martin. "Cooktown Local News". February 6, 2008, pp. 1, 3.]

As tilapia can thrive in fresh, brackish and salt water, ["Aquaponics" [http://www.morningstarfishermen.org/fish.html] ] it is thought that infestation in one river can lead to infestation of neighbouring rivers by the fish swimming from the mouth of one to the other through the sea.

Galapagos Islands, Ecuador

Tilapia have been introduced to Laguna Junco, an older volcanic caldera. [ [http://www.gct.org/aug06_1.html Galapagos Conservation Trust] ] There are no native freshwater fish in the Galapagos, but there are several native invertebrates that spend all or part of their lifecycle in freshwater. At least one, the Galapagos dragonfly, is endemic. Tilapia must be presumed to pose a threat to these invertebrates. The Ecuadorian Park Service is currently (2007) planning an eradication attempt, with the assistance of US Aid for International Development and the US Geological Survey.

Tilapia have been introduced to the mainland of Ecuador, as well as to much of the rest of Latin America, as a fish culture organism.

ee also

*Invasive species
*Tilapiine cichlid
*Tilapia
*Tilapia in aquaculture
*Genus "Tilapia"
*Genus "Sarotherodon"
*Genus "Oreochromis"

Footnotes

External links

*Tilapia project at Australian Centre for Tropical Freshwater Research, James Cook University [http://www.actfr.jcu.edu.au/projects/JCUDEV_015467.html]
*Information on two tialpia pest species from the Australian Centre for Tropical Freshwater Research as PDF downloads: [http://www.actfr.jcu.edu.au/Projects/Pestfish/Profile.htm]