Corbicula

Common name: Exotic freshwater clam 
Scientific name: Corbicula fluminea and Corbicula australis 
Management programme: Exclusion 

Where are they originally from?

Corbicula fluminea is native to eastern Asia, while Corbicula australis is native to Australia. Corbicula fluminea was first found in New Zealand in the Bob’s Landing area of the Waikato River in May 2023. It was later found in the Waikato River from Lake Maraetai Landing to Tuakau. Corbicula australis was found in March 2024 in a small man-made lagoon at the Taupō Aqua Park. 

Why are they a pest?

• Both species are prolific breeders. As hermaphrodites, a single clam can self-fertilise and produce up to 400 juveniles a day and up to 70,000 a year, allowing them to reach extremely high populations.  
• This poses a risk to water-related infrastructure, for example it can clog electricity generation facilities, irrigation systems and water treatment plants.  
• They outcompete native species for food and habitat. 
• Overseas, Corbicula fluminea has proved difficult to control and eradication has never been achieved. 

Where are they found?

• Corbicula thrive in highly oxygenated freshwater lakes and rivers. 
• They are most often found along the water’s edge of lakes and rivers, but can also be found at considerable depths. 
• They can live on top or buried (up to 15cm) in a variety of substrates, including gravel, sand or mud.  
• They have also been found in areas where fresh and saltwater mix, such as estuaries, lagoons or marshes. 

What do they look like?

• Corbicula fluminea is typically larger, reaching up to 50mm wide, with a more inflated, rounded and broader shell 
• Corbicula australis is usually smaller, up to 25–30 mm wide, and slightly less inflated with a more compressed shape. 
• The shell of Corbicula fluminea is yellowish, greenish or brownish with distinct, coarse concentric ridges that are evenly spaced, while its interior is often white or light purple in older individuals.  
• In contrast, Corbicula australis has a pale yellowish to brown shell that is more uniform in colour with finer, less pronounced ridges and a white interior.  

What are the rules?

Exclusion 

Exclusion pests are not known to be present or established in the Bay of Plenty region. The Regional Council is responsible for managing new incursions into the region. Action may be required from landowners or occupiers to support a control operation. 

Controlled Area Notices 

Biosecurity rules are in place to stop the spread of exotic freshwater clams through a mechanism under the Biosecurity Act called a Controlled Area Notice (CAN). Two CANs are in force – one for the Waikato River and another for the Rotorua Te Arawa lakes with additional protections for Lake Ōkataina. Find more information about these controlled area notices on the MPI website. 

How to stop the spread 

If you’re moving between waterways, you can help to reduce the spread of freshwater pests by using the 'Check, Clean, Dry' method. Ensuring your gear and your vessel is free of these harmful species prevents them hitching a ride with you. For more information on best practice, visit the MPI website.