Shellfish

Establishing a shellfish farm

As a shellfish farmer, you need to actively manage your shellfish to keep them healthy and ensure they have enough space to grow. 

Bivalves do not need feeding, and no medicines or chemicals are administered during growing. 

Managing growth

As the shellfish grow, you need to sort them according to their size (known as ‘grading’) and make sure that the farming equipment has the right stocking density, removing stock if necessary (known as ‘thinning’). 

You might also need to add more floating devices to suspended farming equipment as the shellfish get heavier. Oyster bags will also need to be turned frequently. 

Biofouling 

Both bivalves and farming equipment get colonised by other organisms living in the sea, which is called biofouling. It can reduce growth, cause mortalities, and damage equipment. It will not make the shellfish unsafe for eating, but consumers may prefer ‘cleaner’ produce.  

Biofouling can be managed by either manual removal, often daily, or air-drying shellfish and equipment. 

Read more:

• Controlling biofouling on shellfish and gear, Aquaculture Magazine 
• Biofouling Prevention and Management in the Marine Aquaculture Industry, GloFouling
• Fouling in shellfish aquaculture, Applied Shellfish Farming

Predators

You might need to manage bivalve predators to avoid losing produce. Significant predators of both mussels and oysters include starfish and crabs, and birds like eider ducks that feed on mussels. 

Find out more:

• Exclusion strategies for managing shellfish predators, Northeastern Regional Aquaculture Center
• Eider duck species action plan, Living Shetland

Diseases

Scottish waters are currently mostly free from diseases affecting shellfish. There are no treatments for these diseases, so you need to prevent spread by familiarising yourself with the symptoms, checking stock health regularly, and following a biosecurity management plan. 

If you suspect any of the following disease in your shellfish, you are legally required to report it to the Fish Health Inspectorate. Contact the Fish Health Inspectorate to report a listed disease.

Read more about the notifiable diseases and how to spot them:

• Bonamia exitiosa (oysters)
• Bonamia ostreae  (oysters) 
• Perkinsus marinus (Pacific oysters)
• Marteilia refringens (oysters and mussels)
• Mikrocytos mackini (oysters)
• Oyster herpesvirus (Pacific oysters)

Find out more:

• Listed shellfish diseases, the Marine Directorate
• Diseases of molluscs, the Marine Directorate
• Areas in Scotland with listed diseases, the Marine Directorate

Biotoxins

Marine biotoxins can accumulate in bivalves. Food Standards Scotland (FSS) monitors the level of biotoxins in Shellfish Production Areas. See permitted levels of biotoxins in shellfish on FSS.

FSS will issue warnings when biotoxin levels are high. You may then need to take additional measures to ensure that the shellfish is not unsafe or close your farm to harvesting. 

Instructions for how to check biotoxin results and get alerts on FSS website. 

Find out more:

• Marine Biotoxins, SeaFish
• Managing shellfish toxin guidance, Food Standards Agency
• Safer Shellfish: Biotoxin Monitoring, SeaFish

Water quality testing

Water quality testing is mandatory for shellfish production. Testing is at the growers expense and samples have to be sent to Govt approved labs for testing. A list of organisms you need to test for can be found at this link https://www.cefas.co.uk/expertise/laboratory-services-and-analysis/shellfish-testing/ 
Water testing must be carried out prior to production, and during production.
Only Grade A water quality requires no further product action