Tilapia
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| Tilapia buttikoferi in an aquarium | |
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Oreochromis A. Günther,1889 | |
Tilapia is the common name name used for a variety of cichlid fishes of the genera Oreochromis, Sarotherodon, and Tilapia. Tilapias inhabit a variety of fresh and, less commonly, brackish water habitats from shallow streams and ponds through to rivers, lakes, and estuaries. Most tilapias are omnivorous with a preference for soft aquatic vegetation and detritus.
Because of their large size, good flavour, and rapid growth rate, many tilapias are at the focus of major fishing and aquaculture efforts. Set against their value as food, tilapias have acquired notoriety as being among the most serious invasive species in many subtropical and tropical parts of the world. For example Oreochromis aureus, Oreochromis mossambicus, Sarotherodon melanotheron melanotheron, Tilapia mariae, and Tilapia zilli have all become established in the southern United States, particularly in Florida and Texas [1].
Systematics
As a group, the Oreochromis, Sarotherodon, and Tilapia are often referred to as tilapiine cichlids or simply tilapiines, following the work of ichthyologist Ethelwynn Trewavas, who placed these cichlids in the tribe Tilapiini within the family Cichlidae. Also included in this tribe are Danakilia, Iranocichla, Pelmatochromis, Pterochromis, Steatocranus, and Tristamella [2].
Like other cichlids, tilapias have complex reproductive behaviours and guard their eggs and fry. Broadly speaking, tilapias of the genus Tilapia are substratum spawning cichlids, meaning that they form pairs, lay the eggs on the substrate, and then both parents guard the eggs and fry. Oreochromis and Sarotherodon are mouthbrooders, carrying the eggs and fry in their mouths instead of placing them in a nest. All species of Oreochromis are maternal mouthbrooders, meaning that only the female looks after the eggs and fry, with the male offering no protection or help at all. Instead, the male Oreochromis form leks where they compete with one another for further opportunities to mate with females. By contrast, most Sarotherodon species are biparental mouthbrooders, with both parents protecting the eggs and fry. A few Sarotherodon, such as Sarotherodon melanotheron, are paternal mouthbrooders, with only the male caring for the eggs and fry.
Etymology
The genus name Tilapia is a latinisation of the Tswana word for "fish", thiape [3], coined by Scottish zoologist Andrew Smith in 1840 [4]. Some species of Tilapia are sometimes called St. Peter's fish from the account in the Christian Bible (Matthew 17:24−27) about Peter catching a fish that carried a shekel coin in its mouth. The Bible does not describe the fish in question in any detail, however, Sarotherodon galilaeus galilaeus is common in the Sea of Galilee and has been the target of small-scale artisanal fisheries for thousands of years. 0ther fish, eg John Dory, have also been called St. Peter's fish, and as such the most common name in the English language for these fish is simply tilapia. Restaurants and food producers often avoid using tilapia name and instead refer to the fish as whitefish or perch; this is especially common in Europe and the US where consumers are often unfamiliar with tilapia as a food fish.
Fisheries and aquaculture
Although their meat is somewhat bland compared with halibut, salmon, or sea bass, tilapia are a good source of protein and a popular target for artisanal and commercial fisheries. The majority of such fisheries are in Africa, but accidental and deliberate introductions of tilapia into freshwater lakes in Asia have allowed large fisheries to develop in countries with a tropical climate such as Papua New Guinea, the Philippines, and Indonesia [5]. Tilapia species occur in tropical areas, as such in temperate zone localities, aquaculture operations sometimes use waste heat from factories and power stations. [6].
Tilapia species are also among the easiest and profitable fish to farm. This is due to their omnivorous diet, mode of reproduction (the fry do not pass through a planktonic phase), tolerance of high stocking density, and rapid growth. In some regions the fish can be put out in the rice fields when rice is planted, and will have grown to edible size (12–15 cm, 5–6 inches) when the rice is ready for harvest. One recent estimate for the FAO puts annual production of tilapia at about 1.5 million tonnes, a quantity comparable to the annual production of farmed salmon and trout [7]. Unlike salmon, which rely on high-protein feeds based on fish or meat, commercially important Tilapia species eat a vegetable or cereal based diet.
Tilapia as a biological control
Tilapia species are a also potential biological control for certain aquatic plant problems. They have a preference for a floating aquatic plant, duckweed (Lemna sp.) but also consume some filamentous alga [8]. These benefits are, however, frequently outweighed by the negative aspects of tilapia as invasive species (see below).
Tilapia as an invasive species
Tilapia are native to Africa and the Levant, but have been widely introduced into tropical fresh and brackish waters around the world. Some introductions, as in Florida and Texas, were purposeful introductions by government agencies to control invasive aquatic plants. [9]. The fish have been also been deliberately introduced for commercial or industrial scale aquaculture. Because a number of Tilapia spp are large, fast growing, highly fecund, 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 Tilapia spp. have had detrimental effects on ecosystems. On Rennell Island, the Rennell Island Teal became extinct after introduced Oreochromis mossambicus preyed on the young birds.
Tilapia in aquaria
The larger Tilapia species are generally not viewed as good community aquarium fish because they eat plants and tend to be very disruptive, digging up the substrate and fighting with other fish. The smaller west Afrian species, such as Tilapia joka, and those species from the crater lakes of Cameroon are, by contrast, relatively popular. Conversely, in cichlid aquariums Tilapia spp can be mixed well with non-territorial cichlids, armoured catfish, tinfoil barbs, garpike, and other robust but peaceful fish. Some species, including Tilapia buttikoferi, Tilapia rendalli, Tilapia joka, and the brackish water Sarotherodon melanotheron melanotheron, are attractively patterned and decorative fish.
Tilapia in Asian cuisine
Apart from the very few species found in the Levant, such as Sarotherodon galilaeus galilaeus, there are no tilapias endemic to Asia. However, species originally from Africa have been widely introduced and have become economically important as food fish in many countries. China, the Philippines, Taiwan, Indonesia and Thailand are the leading suppliers and these countries altogether produced about 1,100 thousand metric tonnes of fish in 2001, constituting about 76% of the total aquaculture production of tilapia [10] worldwide.
In Taiwan, tilapia is also known as the "South Pacific crucian carp," and since its introduction, has spread to aquatic environments all over the island. Introduced in 1946, tilapia have made a considerable economic contribution, not only providing the Taiwanese people with food, but also allowing the island's fish farmers to break into key markets such as Japan and the United States. Indeed, tilapia has become an important farmed fish in Taiwan for both export and domestic consumption [11]. The Chinese name for the fish is "Wu-Kuo" and was created from the surnames of Wu Chen-hui and Kuo Chi-chang, who introduced the fish into Taiwan.
The Taiwan tilapia is a hybrid of Oreochromis mossambicus and Oreochromis niloticus niloticus.
References
- Tilapia, ITIS Standard Report. (2004-05-11)
- Tilapias as alien aquatics in Asia and the Pacific: a review FAO report
- Managing Iowa Fisheries: Tilapia Culture in Iowa
- World Seafood Market Article on the growth of tilapia aquaculture
External links
- Tilapia Fish Site devoted to Tilapia fish.
- American Tilapia Association
- Taiwan Tilapia Alliance
- Yahoo seafood group
- The Tilapia Project
- Environmental concerns