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Potentially Misidentified Species:
The blue tilapia, Oreochromis aureus, and the blackchin tilapia Sarotherodon melanotheron also occur
as exotic species in Florida. They sre superficially quite similar to
Oreochromis mossambicus, but species-specific markings (e.g., the black
chin of S. melanotheron which O. aureus lacks) as well as
differing spine/ray counts are sufficient to differentiate the species from one
another.
II. HABITAT AND DISTRIBUTION
Regional Occurrence:
In their native range along the eastern coast of Africa, Oreochromis
mossambicus occurs in riverine and coastal lagoon habitats. The species
was introduced to the U.S. by the aquarium and aquacultures trades and were
released either accidentally or intentionally into waterways of Texas, Florida
and Alabama (Brown 1961, Courtney et al. 1974, Bruton and Bolt 1975, Whiteside
1975, Lee et al. 1980). Riedel and Costa-Pierce (2005), describe the existence
of a large southern California population of O. mossambicus within the
Salton Sea and known locally as Salton Sea tilapia.
Centers of abundance in Florida include Dade, Brevard, Indian River, and
Hillsborough counties, and Courtney et al. (1974) suggest each of these
represents an independent introduction event.
IRL Distribution:
Within the IRL region, Mozambique tilapia have been found in the Brevard and
Indian River counties. Courtney, et al. (1974), cites these as the result of
distinct introductions events.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
The maximum size of the Oreochromis mossambicus tends to vary based on
its geographical location. Collections from within the native range indicate a
maximum size of around 430 mm, while animals in the Gulf of Mexico measured a
maximum of 360mm (Bruton and Allanson 1974, Lee et al, 1980).
O. mossambicus are long-lived surviving to approximately 11 years
(Boschung and Mayden 2004, Fryer and Illes 1972).
Abundance:
Specific abundance information relative to Oreochromis mossambicus in
Florida is sparse, other than statements by authorities that the species is
established in several counties and reported as occurring with unknown reproductive status
in others.
Dial and Wainright (1983) suggest that actual abundance of this species in
Florida has been obscured by confusion of Mozambique tilapia and blackchin
tilapia, Sarotherodon melanotheron, by commercial fishermen.
Reproduction:
Female Oreochromis mossambicus mature at approximately 150-160 mm, and
males mature at approximately 170-180 mm (Hodgkiss and Man 1978, Arthington and
Milton 1986). Males construct nests in sparse to moderately vegetated bottoms
where fertilization of the eggs takes place (Bruton and Bolt 1975). Several
different females will lay eggs in the nest. Females can lay between 50-1,780
eggs, based on individuals' size and environmental conditions. (Trewevas
1983). Males are generally aggressive and ritualistic during reproductive season,
although male-male confrontations rarely actually become violent (Bruton and
Bolt 1975).
Embryology:
Once fertilized, the female Oreochromis mossambicus takes the eggs into
her buccal cavity (mouth) and broods them until hatching. Hatching occurs in
approximately 3-5 days. Once hatched, the females continue to mouth-brood the
fry until they are approximately 14-21 days old. Male O. mossambicus
are reported to occasionally mouth-brood eggs and fry as well (Bruton and Bolt
1975, Arthington and Milton 1986).
IV. PHYSICAL TOLERANCES
Temperature:
Mozambique tilapia was found to have a lower lethal limit of 9.5°C under
laboratory conditions (Shafland and Pestrak 1982). Trewevas (1983) similarly
reported that Oreochromis mossambicus does not tolerate temperatures
below 10°C. This temperature limits its distributional range, although some
studies suggest the species may exploit thermal refuges similar to other
cichlids such as the blue tilapia, O. aureus, to move somewhat further
north (Hubbs et al. 1978). Adult O. mossambicus will migrate to deeper
waters as cold temperatures set in (Bruton and Boltt 1975 Arthington and
Milton 1986).
Salinity:
Oreochromis mossambicus have a broad salinity tolerance (Trewevas 1983).
They can survive from freshwater up to 40 ppt, and are capable of spawning in
estuarine waters at salinities as high as 34.5 ppt (Knaggs 1977,
Dial and Wainright 1983). Florida populations are typically found in fresh to
estuarine waters, however they appear to only inhabit freshwater lakes and
ponds in Texas (Courtney et al. 1974, Shafland and Pestrak 1982).
V. COMMUNITY ECOLOGY
Trophic Mode:
Oreochromis mossambicus are generalist/opportunistic omnivores that
consume detrital material, vegetation ranging from diatoms to macroalgae to
rooted plants, invertebrates, and small fish (Bowen 1979, Mook 1983, Trewevas
1983). Diets differ depending on location-specific resource availability. De
Silva et al. (1984) report O. mossambicus populations in different
lakes ate different diets and trophic strategies ranged from detritivory, to
herbivory, to near-exclusive carnivory with individuals preying on small fish
and invertebrates.
Associated Species:
Oreochromis mossambicus co-occurs with a number of other non-native
tilapia species in Florida. Possible hybridization between Mozambique tilapia
and blue tilapia (O. aureus) has been reported in Florida, e.g., in Dade County
drainage canals (Shafland 1996).
VI. INVASION INFORMATION
Invasion History:
Oreochromis mossambicus have been both intentionally and accidentally
released to many non-native areas worldwide in a variety of ways and for a
number of reasons. Intentional release has often been for purposes of plant or
pest (e.g., mosquito) control, although Moyle (1976) notes that population
densities often failed to grow large enough to effectively control insect or
plant populations. Intentional release has also occurred in attempts to
establish populations to be utilized as sportfish, bait fish, or commercial
stocks, while accidental release has occurred at a number of hatcheries, fish
farms, aquariums and zoos (Shapovalov et al. 1981, Dial and Wainright 1983, Grabowski et al. 1984, Courtenay and Stauffer
1990).
In Florida, O. mossambicus was first introduced into Dade County during
the 1960s where it first became established (Hogg 1976, Courtenay and Stauffer 1990). The
species was introduced into the Indian River Lagoon basin either as releases or
escapes from fish farms or aquarium owners (Courtenay et al. 1974, Dial and
Wainright 1983). Courtney et al. (1984) reported the probable release of the
fish in the IRL watershed by a developer to control plant growth.
O. mossambicus individuals have been collected in Everglades National
Park and have been reported as present within the greater Everglades drainage
(Tilmant 1999, Nico 2006).
Nico (2006) reports that O. mossambicus is established or locally
established in seven states (Arizona, California, Colorado, Florida, Hawaii,
Idaho, and Texas) and formerly locally established but no longer extant in
Georgia, Montana, and North Carolina. The author also and reports O. mossambicus from Alabama, Illinois, and
New York, but they appear to not be established there.
Costa-Pierce (2003) suggests that the mouth-brooding maternal habit of the
species is important as a mechanism of dispersal and establishment for founder
populations of O. mossambicus.
Potential to Compete With Natives:
Oreochromis mossambicus pose threats to local native populations through
competition for food and nesting space (Courtenay et al. 1974). This
interaction may reduce the biodiversity of the native fishery due to reduction
of food availability and/or by the native fish being eaten as prey (Neil 1966,
Bruton and Boltt 1975). In Hawaii, striped mullet (Mugil cephalus) are
threatened because of the introduction of this species. Mozambique tilapia may
also be responsible for the decline of the desert pupfish, Cyprinodon
macularius, in California's Salton Sea (Courtenay and Robins 1989, Swift et
al. 1993).
Courtenay (1989) predicts that the Mozambique tilapia could eventually become
established within the Florida Everglades, with potentially devastating
effects.
Oreochromis mossambicus has been nominated by the Invasive Species
Specialist Group (ISSG) as among "100 of the World's Worst" invasive alien
species.
Possible Economic Consequences of Invasion:
Mozambique tilapia are hardy individuals that are easy to grow, which makes
them an ideal aquaculture species. Tilapia have a mild, white flesh that
appeals to consumers, making them economically important food fish. This
species contributes about 4% of the total tilapia aquaculture production
worldwide, and is valued more when used for hybridization (Gupta and Acosta
2004). However, because of this hardiness, they can out-compete native species
when released into the natural environment. This may displaces or eliminate native species.
VII.
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Report by:
J. Masterson, Smithsonian Marine Station
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