The Asian clam is a freshwater shellfish, and an invasive non-native species. They are native to eastern Asia and now spreading within UK canals and rivers.
Asian clams compete with native species for food and space. Photo credit: NNS
Asian clam facts
Scientific name: Corbicula fluminalis
Family: Corbiculidae
Diet: Plankton
Size: Usually less than 30mm
Weight: 4-12g
Lifespan: 2-4 years
Asian clams in Britain
Asian clams were first recorded in Britain on the Norfolk Broads in 1998, and recently spotted on sections of our canals. This includes on the Shropshire Union, near Chester.
Asian clams reproduce and grow rapidly, forming large colonies which can attach to submerged surfaces - clogging pipes, and covering lock gates and boats. An adult clam can produce around 70,000 juveniles in a single year.
Climate change is also likely to affect their spread in Britain, with milder winters and warmer summers boosting reproduction. Asian clams need temperatures to be above 15 degrees Celsius to breed.
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Why are Asian clams a problem for canals and native wildlife?
Asian clams can accumulate in large colonies, which block pipes and cover structures. Removing these colonies and repairing any damage can be expensive. Asian clams can also affect the balance of oxygen and nutrients in water, which means they outstrip resources for other native species to compete and alter the balance of the freshwater ecosystem itself.
Asian clam larvae can drift along by water currents, but are also dispersed by wading waterfowl, fish, birds - and by people.
Like other invasives such as the Zebra mussel, clams can spread through recreational boating and angling, with clams attaching themselves to a boat's hull or equipment and then transported to other waterways.
They are also able to survive out of water in cold, damp conditions for several weeks. Because of this, it is important to follow the 'Check, Clean, Dry' process each time you exit a canal or river to prevent their spread - even if you're relocating to another area close by.
Help stop the spread of invasive species by practising 'Check, Clean, Dry' each time you leave a stretch of canal
How to identify Asian clams
Asian clams are yellow-brown, with a globular shell with a rounded to triangular outline. They are typically less than 30mm in size, and have raised, regular and concentric ribs on their shells.
They can be found in canals, streams, rivers, lakes and drainage/irrigation channels.
How do Asian clams breed?
Asian clams are hermaphrodites, meaning they can self-fertilise or cross-fertilise with other clams.
A single mature adult is able to release hundreds of microscopic juveniles per day, which can accumulate to tens of thousands over a breeding season. These juveniles drift along in the water currents before settling onto a canal bed or embankment to mature, which takes between three and six months.
Asian clams have few predators in the UK, making their population difficult to control. Photo credit: NNS
How can I help stop the spread of Asian clams and other invasive species?
As well as following the Check, Clean, Dry procedure when exiting the water, you can also record your sightings on INNS Mapper.
INNS Mapper is a free, open access tool, used to report and share survey and management information, which will help coordinate effective management of invasives.
