Photographer: Michael Rupert Hayes Source: commons.wikimedia.org Copyright: (CC BY-SA 2.0)
Adults range from about 5-8 inches in length and can weigh 5-6 pounds; however, the largest recorded specimen was up to 21 inches and weighed more than 10 pounds. Oreochromis aureus has a blue-grey body with a white belly and 20 to 26 gill rakers. The caudal fin of the blue tilapia has broad bright red or pink distal margin. The head of the male fish will change into a bright metallic blue shade, during the breeding season, and he will also display a vermilion pigmentation on the edge of his dorsal fin and an intense pink coloring on the margin of his caudal fin. A breeding female fish will develop a pale orange color on the edges of her dorsal and caudal fins.
When Oreochromis aureus is present it can diminish plant, fish and shrimp diversity in freshwater areas. Blue tilapia has also been implicated as the cause for unionid mussel declines in two Texas water bodies, Tradinghouse Creek and Fairfield reservoirs. With a wide range of temperature toleration, the blue tilapia has been able to establish itself within the Southern Gulf States but could travel northwards. Oreochromis aureus is considered a competitor with native species for spawning areas, food, and space. Some streams where Oreochromis aureus is plentiful have lost most vegetation and nearly all native fishes. It has been shown in several states that the blue tilapia's local abundance and high densities in certain areas have resulted in marked changes in fish community structure. All species from the genus Oreochromis readily hybridize, potentially posing a threat to genetic diversity through introgression. If two species from the genus hybridize, that can increase their survivability and expand their invasive range.
Overall, the cichilidae family is known to be adaptable to temperature and salinity variations and Oreochromis aureus is no exception. Despite being a tropical fish, the blue tilapia can survive in temperatures ranging from 10°-30°C and also can tolerate fairly brackish conditions. Oreochromis aureus can reproduce in both freshwater and brackish water conditions. Oreochromis aureus inhabits warm ponds well as lakes and streams, in open water as well as among stones and vegetation, feeding mainly on phytoplankton and sometimes zooplankton. Young fish have a more varied diet which includes large quantities of copepods and cladocerans but they also take pieces of small invertebrates. Blue Tilapia are mouthbrooders, and broods range from 160 to 1600 eggs per female. Sexual maturity can be reached at age of 5-6 months, in ponds.
This species has been introduced through a combination of means; including stocking and experimental work by states and release by individuals seeking have another species of sport fish. Oreochromis aureus has also been introduced as food for predatory fish, as a human food source, and as a means of aquatic plant control. However, the impact of this invasive species was not taken into consideration when introductions occurred. The exact reasons for and sources of some introductions are uncertain (e.g., Texas). Apparently, power companies became interested in using so-called "tropical fishes" for food or sport in heated effluent ponds used to cool effluents from both fossil fuel fired and nuclear generating plants, where temperatures often became too high to support populations of native fishes. Blue tilapia and redbelly tilapia were inadvertently introduced into Hyco Reservoir in North Carolina in 1984 after a small number of fish escaped from a holding cage located in the heated discharge area during an on-site agricultural study; other mismanagement incidences like these have allowed the blue tilapia to establish itself within several United States.
Northern and Western Africa and the Middle East
U.S. Habitat: Fresh or brackish waters, ranging from creeks and streams to lakes. The blue tilapia is adaptable to salinity levels allowing it to inhabit and reproduce in both freshwater and brackish areas.
Distribution
U.S. Present: AL, AZ, CO, FL, ID, MS, NC, NV, OK, PA and TX
Chemical treatment is not efficient for controlling fish populations because of the effects it would have on vegetation and aquatic invertebrates. To help control populations there should be an encouragement to fish blue tilapia with no intentions of “catch and release”. Educating the public anglers of the threat, it could help manage the populations. Thankfully, it is now a prohibited exotic species in Texas but being established means it would require a lot of time and money to eradicate the blue tilapia.
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Canonico, G. C., Arthington, A., McCrary, J. K., & Thieme, M. L. 2005. The effects of introduced tilapias on native biodiversity. Aquatic Conservation: Marine and Freshwater Ecosystems, 15(5):463-483.
D'Amato, M.E., M.M. Esterhuyse, B.C.W. van der Waal, D. Brink, and F.A.M. Volckaert. 2007. Hybridization and phylogeography of the Mozambique tilapia Oreochromis mossambicus in southern Africa evidenced by mitochondrial and microsatellite DNA genotyping. Conservation Genetics 8: 475-488.
Howells, R. G. 1995. Losing the old shell game: could mussel reproductive failure be linked to tilapia? Info-Mussel Newsletter 3(8):4.
Noble, R. L., & Germany, R. D. 1986. Changes in fish populations of Trinidad Lake, Texas, in response to abundance of blue tilapia. Fish culture in fisheries management. American Fisheries Society, Fish Culture Section and Fisheries Management Section, Bethesda, Maryland, 455-461.
Scoppettone, G. G., Rissler, P. H., Nielsen, M. B., & Harvey, J. E. 1998. The status of Moapa coriacea and Gila seminuda and status information on other fishes of the Muddy River, Clark County, Nevada. The Southwestern Naturalist, 115-122.
Scoppettone, G. G., Rissler, P. H., Gourley, C., & Martinez, C. 2005. Habitat Restoration as a Means of Controlling Non‐Native Fish in a Mojave Desert Oasis. Restoration Ecology, 13(2):247-256.
Zale, A. V., & Gregory, R. W. 1990. Food selection by early life stages of blue tilapia, Oreochromis aureus, in Lake George, Florida: Overlap with sympatric shad larvae. Florida Scientist, 53(2):123-129.
Zambrano, L., Martínez-Meyer, E., Menezes, N., & Peterson, A. T. 2006. Invasive potential of common carp (Cyprinus carpio) and Nile tilapia (Oreochromis niloticus) in American freshwater systems.
Internet References
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