Everything about Tilapia As Exotic Species totally explained
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. Across much of Asia and Africa they've been introduced into ponds and waterways for the purposes of aquaculture. In other cases, unwanted fish have been released by aquarists or ornamental fish farmers into the wild.
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.
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.
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 isn't known for certain. The Salton Sea tilapia feed on plant material,
phytoplankton (particularly
diatoms),
copepods,
rotifers,
barnacle larvae, and small
annelid worms. 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.
There are also populations of tilapia in two lakes in Texas; one in Fairfield lake, the other in Martin Creek 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. Later genetic studies indicated that at least two separate introductions to the native creeks and rivers occurred. 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 . In 1981 they were also noted to be present in the waters of Carnarvon,
Western Australia .
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 . 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 . 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, and are spreading rapidly into previously untouched and relatively pristine river systems such as the
Endeavour River near
Cooktown.
As tilapia can thrive in fresh, brackish and salt water, it's 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. 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.
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