Tilapia as exotic species

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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. [1] Across much of Asia and Africa they have been introduced into ponds and waterways for the purposes of aquaculture. [2] In other cases, unwanted fish have been released by aquarists or ornamental fish farmers into the wild.[3] [4]

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 many places, particularly Florida and Australia, feral populations of tilapiine cichlids have had detrimental effects on ecosystems. [5] [6]

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[edit] Singapore

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 favour 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.

[edit] Solomon Islands

On Rennell Island (Solomon Islands), the Rennell Island Teal became extinct after introduced Oreochromis mossambicus preyed on the young birds.[citation needed]

[edit] United States

In the 1930s fish were introduced to the Salton Sea in the desert of Southern California in hopes of making it a tourist destination for fishing enthusiasts. It worked: the fish thrived, or at least the tilapiine cichlids, primarily Oreochromis spp., did — at one time there were 100 million Oreochromis in the Salton Sea. But salty water carries less oxygen than fresh water, so as the lake grew saltier, oxygen stores were depleted, and hot water carries less oxygen than cold water, so in late summer, the fish suffocate at a rate of about ten million a week, leaving blankets of dead Oreochromis miles long and miles wide along the shore. This annual die-off attracts flies. Flies lay eggs, which hatch into maggots, which get into the water. Some of these maggots carry botulism. The surviving fish eat the infected maggots and contract botulism. These fish are then eaten by birds. The birds die. There are people at the Park Service whose entire job description in the summer is to round up the sick and dead pelicans. (Because California's coastal wetlands are gone, the Salton Sea area has become a crucial haven for migrating birds.) Finally, the dead fish that end up back in the lake serve as nutrients for algae, leading to enormous, malodorous algae blooms, which feed the surviving fish and allow them to partially replenish their stocks for next summer's die-off. The fishery at the Salton Sea has been called among the most productive in the world. The Sea has Oreochromis, gulf croaker, corvina, and sargo. The tilapia weigh up to 3.5 pounds. A day of fishing may net over one hundred tilapia. Some have even caught hundreds. There is no limit to the number of tilapiine cichlids that can be caught.

[edit] 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. [7] Later genetic studies indicated that at least two separate introductions to the native creeks and rivers occurred.[8] 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 [9]. In 1981 they were also noted to be present in the waters of Carnarvon, Western Australia [10].

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 [8]. 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.

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 [11]. 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.

[edit] See also

[edit] References

  1. ^ Florida's Exotic Freshwater Fishes. State of Florida (2006). Retrieved on 2007-02-10.
  2. ^ Nand Lal, Satya; Roberto Foscarini. Introduction of tilapia species and constraints to tilapia farming in Fiji. Food and Agriculture Organization of the United Nations. Retrieved on 2007-02-10.
  3. ^ University of Southern Mississippi/College of Marine Sciences/Gulf Coast Research Laboratory (2005-08-03). Fact Sheet for Tilapia zilli (Gervais, 1848). Gulf States Marine Fisheries Commission. Retrieved on 2007-02-10.
  4. ^ Fuller, Pam L.; Leo G. Nico (2002-10-11). Nonindigenous Fishes of Florida - With a Focus on South Florida. U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology. Retrieved on 2007-02-10.
  5. ^ Nico, Leo (2006-04-22). Tilapia mariae. USGS Nonindigenous Aquatic Species Database. Retrieved on 2007-02-10.
  6. ^ Tilapia - NSW DPI - Fisheries. NSW Department of Primary Industries: Fisheries. Retrieved on 2007-02-10.
  7. ^ McCutcheon, Peter (2005-01-01). Tilapia spreads in nth Qld. Australian Broadcasting Corporation. Retrieved on 2007-03-01.
  8. ^ a b Mather, P.B.; A.H. Arthington. An assessment of genetic differentiation among feral Australian tilapia populations. Australian Journal of Marine and Freshwater Research. Retrieved on 2007-03-01.
  9. ^ Cadwallader, P.L.; G.N. Backhouse and R. Fallu (1980-01-01). Occurence of exotic tropical fish in the cooling pondage of a power station in temperate south-eastern Australia. Australian Journal of Marine and Freshwater Research. Retrieved on 2007-03-01.
  10. ^ Aquatic Invaders - Introduced species are a threat to our aquatic biodiversity: Tilapia or Mozambique Mouthbrooder. Department of Fisheries, Government of Western Australia (2006-06-01). Retrieved on 2007-03-01.
  11. ^ McDonald, Ian (2005-07-21). Press Release - Tilapia under attack. Ian McDonald Federal Minister for Fisheries and Conservation at the time. Retrieved on 2007-03-01.
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