Taxonomic name: Oreochromis spp.
Common names: boulti, freshwater snapper, mojara, ngege, pla nil, St. Peters fish, tilapia
Organism type: fish
Tilapia (Oreochromis spp.) is the common name applied to three genera of fish in the family Cichlidae: Oreochromis, Sarotherodon and Tilapia. These include over 70 species of fish, at least eight of which are used for aquaculture. Tilapia belong to a family of fish known as cichlids, among which most African members are mouthbrooders. The cage culturing of tilapia results in a reduction of water quality in the surrounding environment, which is particularly worrying when close to ecologically important areas. The unavoidable escape and establishment of wild tilapia from cages has sometimes resulted in other serious problems, such as the decline of culturally valued native fish species, particularly cichlids, and the alteration of natural benthic communities.
estuarine habitats, lakes, marine habitats, water courses, wetlands
Tilapia (Oreochromis spp.) exhibit maximum growth rates at temperatures between 25 and 30°C (Meyer 2002), making them more likely to become established and invasive in tropical climates. However, both tolerance to water temperature and to salinity varies greatly between species. Nile tilapia (O. niloticus) are the least cold tolerant of the farmed tilapia and prefer tropical to subtropical climates. Blue tilapia (O. aureus) is able to tolerate temperatures as low as 8-9°C, making it more likely to establish in countries with pronounced seasonal temperature variations (Gupta and Acosta 2004).
Tilapia usually inhabit freshwater habitats, but some species and hybrids are known to be highly euryhaline (capable of tolerating a wide range of salt water concentrations). Blue tilapia, redbelly tilapia (Tilapia zillii) and a red tilapia hybrid (O. mossambicus and O. hornorum) are extremely tolerant of saline waters and used in seawater aquaculture. Saline tolerance is also evident in other red tilapia hybrids, gallilee tilapia (Sarotherodon galilaeus), black-chinned tilapia (S. melanotheron) and Mozambique tilapia (O. mossambicus) and Zanzibar tilapia (O. hornorum) (Gupta and Acosta 2004).
Please follow this link for a description of the impacts of this species 'general impacts' compiled by the ISSG.
Today tilapia (Oreochromis spp.) makes up about 3.5% of the total amount of global aquaculture production. Nile tilapia (Oreochromic niloticus) is the most predominant species of tilapia cultured, but at least seven other and a number of hybrids are also commonly farmed (Gupta and Acosta 2004). Tilapia are well adapted to artificial culture environments, gain weight quickly at optimum conditions and reproduce on the farm without special management or infrastructure (Meyer 2002). About 85 countries farm tilapia on some scale including China (an aquaculture giant responsible for half the total production of tilapia) and many South East Asian countries. A huge 98% of these tilapia farms occur outside the fish’s native habitat (FOA 2002, Shelton 2002, in Gupta and Acosta 2004). Tilapia is generally produced in relatively low-input farms for both domestic markets and exportation. Earthen ponds and cage culture in open water bodies are the most common culture systems. Development of the tilapia trade and marketing coupled with the development of the aquaculture industry is becoming more intensive as the fisheries industry comes to rely more and more on fish harvested from farms rather than sea-caught fish. For example, the Genetically Improved Tilapia programme (based on selective breeding) produced a strain of O niloticus with growth rate increased by 85% (Eknath and Acosta 1998, in Gupta and Acosta 2004). Hybrids of tilapia have also been used to create increasingly adaptable and hardy fish (commonly referred to as red or golden tilapia). Concerns have been raised about the environmental risk of introductions of ever-improved strains and hybrids of tilapia environmental risk.
As males grow faster and are more uniform in size than the females manual sexing techniques and reverse sex hormones have been used for tilapia farming. Hybridisation between certain Oreochromis species has also been used to create male-only offspring generations (Lazard 1996, in Gupta and Acosta 2004).
Native range: Tilapia (Oreochromis spp.) are native to Africa and the Middle East (Gupta and Acosta 2004).
Introduced range: Tilapia (Oreochromis spp.) were introduced to the Far East in the 1940s for farming purposes. O. mossambicus, one of more commonly farmed tilapia species, was first introduced into the Caribbean by C.F. Hickling in 1947. It was quickly disseminated by humans throughout Central and South America. O. aureus and O. niloticus and several red hybrid strains were introduced in the 1960s and 1970s (Fitzsimmons 2002).
Introduction pathways to new locations
Aquaculture: Cage culture of tilapia (Oreochromis spp.) in natural open water bodies has promoted the worldwide proliferation of the fish and allowed for its introduction into new geographic regions, escape into the wild and establishment in native ecosystems. A survey conducted Mexico revealed the presence of wild tilapia in 50% of intensive cage culture sites visited (Schmitter-Soto and Caro 1997). Escape was perhaps due to cage-damage from large animals or increases in the water level, but there are a myriad of easily imaginable scenarios by which tilapia could spread into adjacent natural habitat
Other: Intentional unofficial release of fish into new locations or environements: In Mexico it is suspected that the intentional release of tilapia (Oreochromis spp.) into water bodies is responsible for its detection in lakes that it has never been previously officially farmed (and that are not connected to water bodies where tilapia is farmed) (Schmitter-Soto and Caro 1997).
Local dispersal methods
Natural dispersal (local): Natural spread: Tilapia (Oreochromis spp.) are natural schooling fish and are able to migrate long distances (Stauffer 1984, Trewavas 1983, Fryer and Iles 1972, in Gutierrez and Reaser 2005).
Preventative measures: The use of potentially invasive alien species for aquaculture and their accidental release/or escape can have negative impacts on native biodiversity and ecosystems. Hewitt et al, (2006) Alien Species in Aquaculture: Considerations for responsible use aims to first provide decision makers and managers with information on the existing international and regional regulations that address the use of alien species in aquaculture, either directly or indirectly; and three examples of national responses to this issue (Australia, New Zealand and Chile). The publication also provides recommendations for a ‘simple’ set of guidelines and principles for developing countries that can be applied at a regional or domestic level for the responsible management of Alien Species use in aquaculture development. These guidelines focus primarily on marine systems, however may equally be applied to freshwater.
Copp et al, (2005) Risk identification and assessment of non-native freshwater fishes presents a conceptual risk assessment approach for freshwater fish species that addresses the first two elements (hazard identification, hazard assessment) of the UK environmental risk strategy. The paper presents a few worked examples of assessments on species to facilitate discussion. The electronic Decision-support tools- Invasive-species identification tool kits that includes a freshwater and marine fish invasives scoring kit are made available on the Cefas (Centre for Environment, Fisheries & Aquaculture Science) page for free download (subject to Crown Copyright (2007-2008)).
Please follow this link for details on control of this species 'management information' compiled by the ISSG.
The feeding habits of tilapia (Oreochromis spp.) are very broad, considering they feed on benthic algae, phytoplankton, macrophytes, zooplankton, fish eggs, fish larvae, and detritus (Alceste and Jory 2000). At least one species, Mozambique tilapia (O. mossambicus), has been observed to prefer feeding on macrophytes (aquatic plants), switching to an omnivorous diet only when such sources are depleted or absent (Riedel 1965, in Ven den Berghe Undated). It has been noted that several species of tilapia are stimulated to include fish fry in their diet under oligotropic low-nutrient conditions (Riedel 1965, De Moor et al. 1986, Popma and Green 1990, in Ven den Berghe Undated).
Nile tilapia (Oreochromis niloticus) and blue tilapia (O. aureus) reach sexual maturity at about 5 to 6 months. Mozambique tilapia (O. mossambicus) exhibits early reproduction with sexual maturity occurring at 8-9cm (Gupta and Acosta 2004).
Female tilapia may reproduce once every two months under optimal conditions, with O. mossambicus, for example, laying 300 to 500 eggs each time (equivalent to a maximum of 3600 eggs per year) (Riedel 1965, in Ven den Berghe Undated).
Members of Oreochromis spp. commonly exhibit the following sequence of reproductive events (Riedel 1965, Fryer and Iles 1972, in Ven den Berghe Undated). The male will dig a “nest” or “display site” in which to court females. These are constructed in sandy or muddy ground, are up to 15cm deep and 100cm wide, and are subject to aggressive defence (McCraryet al. 2001, in Ven den Berghe Undated). The entire bottom of a water body can become covered with these craters, which may become so densely packed that they resemble cells on a bee hive (Mc Kaye et al. 1995, in Ven den Berghe Undated). The male fertilises the eggs that have been laid by the courted female. The female will then incubate the eggs directly inside her mouth for three to five days. Larvae will hatch and will be retained in her mouth for a further two weeks. The female will guards her free-swimming young, which hide in her mouth when danger threatens.
Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Thursday, 12 January 2006