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   Corbicula fluminea (mollusc)   
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    Taxonomic name: Corbicula fluminea (O. F. Müller, 1774)
    Synonyms: Corbicula fluminalis (Muller, 1774), Corbicula leana (Prime), Corbicula manilensis (Philippi, 1884)
    Common names: Asian clam (English), Asiatic clam (English), prosperity clam (English)
    Organism type: mollusc
    Corbicula fluminea is a freshwater clam that has caused millions of dollars worth of damage to intake pipes used by power, water, and other industries. Many native clams are declining as C. fluminea outcompetes them for food and space. C. fluminea requires well-oxygenated waters and prefers fine, clean sand, clay, and coarse sand substrates. C. fluminea spreads when it is attached to boats or carried in ballast water, used as bait, sold through the aquarium trade, and carried with water currents.
    Description
    Corbicula fluminea has a yellowish brown to black shell with concentric, evenly spaced ridges on the shell surface (INHS 1996). They are usually less than 25mm but can grow up to 50 to 65mm in length (Aguirre and Poss 1999).
    Similar Species
    Sphaeriidae

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    Occurs in:
    estuarine habitats, lakes, water courses
    Habitat description
    Corbicula fluminea is found in lakes and streams of all sizes with silt, mud, sand, and gravel substrate (INHS 1996). They can tolerate salinities of up to 13 ppt for short periods (Aguirre and Poss 1999) and temperatures between 2 and 30 degrees Celsius, or 86 degrees Fahrenheit, (Balcom 1994). It prefers fine, clean sand, clay, and coarse sand substrates (Aguirre and Poss 1999). It is usually found in moving water because it requires high levels of dissolved oxygen. C. fluminea is generally intolerant of pollution.
    General impacts
    Ecologically, C. fluminea can outcompete many native clam species for food and space (PNNL 2003). The introduction of C. fluminea into the United States has resulted in the clogging of water intake pipes, affecting power, water, and other industries. Nuclear service water systems (for fire protection) are very vulnerable, jeopardising fire protection. In 1980, the costs of correcting this problem were estimated at 1 billion dollars annually. C. fluminea causes these problems because juveniles are weak-swimmers, and consequently they are pushed to the bottom of the water column where intake pipes are usually placed. They are pulled inside the intakes, where they attach, breed, and die. The intake pipe become clogged with live clams, empty shells, and dead body tissues. Buoyant, dead clams can also clog intake screens.
    Uses
    In Corbicula fluminea's native range, it is marketed for human consumption and as feed for domestic fowl (Aguirre and Poss 1999). In the United States, it is sold as fish bait (Aguirre and Poss 1999), and it is sold through the aquarium trade where they are known as "pygmy" or "gold" clams.
    Geographical range
    Native range: C. fluminea is native to southeastern China, Korea, southeastern Russia, and the Ussuri Basin (Aguirre and Poss 1999).
    Known introduced range: In the United States, C. fluminea has been introduced to 38 states and the District of Columbia (Foster et al. 2000).
    Introduction pathways to new locations
    Other: Used as live bait throughout the United States. The clams sometimes escape into the water alive.
    Pet/aquarium trade: Corbicula fluminea is known as "pygmy" or "gold" clams in the aquarium trade.
    Ship ballast water: Juvenile clams can be carried in ballast water all over the world.
    Ship/boat hull fouling:


    Local dispersal methods
    Boat:
    Escape from confinement: Researchers sometimes inadvertently release C. fluminea into non-native waters.
    Water currents: Water currents spread juveniles throughout a water body.
    Management information
    Corbicula fluminea populations are controlled by a variety of methods. Where intakes pipes are fouled, thermal regulation is employed, whereby water in the pipes is heated to temperatures exceeding 37 degrees Celsius. But this method is not possible in most existing water systems. Mechanical measures, such as using screens and traps, can effectively eliminate older clams and remove body tissue and shells from the system. Chemicals, such as small concentrations of chlorine or bromine, are used to kill juveniles and sometimes adults. This method is very effective, but because of increasing restrictions on the amounts of these chemicals that may be released from a facility, facility managers have been moving away from this method. Some states have legislation prohibiting the introduction of C. fluminea into their waters.
    Nutrition
    Corbicula fluminea feeds on plankton.
    Reproduction
    Corbicula fluminea is a hermaphrodite (both sexes are found on one organism) and is capable of self-fertilisation. Sperm is released into the water, caught by another clam, and brooded in the gills. The larvae are released through the excurrent siphon and sent out into the water column. Spawning can continue year around in water temperatures higher than 16 degrees Celsius. The water temperature must be above 16 degrees Celsius for the clams to release their larvae. In North America, spawning occurs from spring to fall (Aguirre and Poss 1999). Maximum densities of C. fluminea can range from 10,000 to 20,000 per square metre, and a single clam can release an average of 400 of juveniles a day (PNNL 2003) and up to 70,000 per year. Reproductive rates are highest in fall (Aguirre and Poss 1999).
    Lifecycle stages
    Larvae spawned late in spring and early summer can reach sexual maturity by the next fall (Aguirre and Poss 1999). C. fluminea maximum lifespan is 7 years, but it varies according to habitat (Aguirre and Poss 1999), with an average lifespan of 2 to 4 years (PNNL 2003).
    Reviewed by: Anon
    Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Monday, 24 January 2005


ISSG Landcare Research NBII IUCN University of Auckland