Species Description: The Mozambique tilapia, Oreochromis mossambicus, is native to Africa but has been introduced to Florida and elsewhere as well.
Individuals collected in their native range typically reach 380 mm SL (standard length, measured from the snout to the caudal peduncle), while animals collected elsewhere (e.g., the Gulf of Mexico) may reach only around 220 mm. Males grow slightly larger than females. Females and non-breeding males are mainly silver in color with 2-5 blotches along the midline and occasionally the dorsal fin. Breeding males are black with white Mozambique tilapia have 28-31 vertebrae and 14-20 lower gill rakers. The spine/ray count is: Dorsal = XV-XVII + 26-29; Anal = III=iV + 9-10. (Texas State University).
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.
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 aquaculture 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.
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).
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).
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).
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.
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 displace or eliminate native species.
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