Bivalve Mollusc Safety — Seafish

Delivering Safe Bivalves to the Market

There are specific requirements to ensure bivalve molluscs are safe for us to eat by reducing the risks from microbial contamination and biotoxins.

Seafood is a good source of protein, and shellfish have been shown to have many health benefits. Farmed UK shellfish are one of the most sustainable forms of food for us to eat, with very low impacts and increasingly recognised benefits to the wider environment.  

Water quality, in terms of the bacteria and viruses present, affects the incidence of microbial contamination (bacterial and viral) in shellfish. If shellfish are eaten raw or is only lightly cooked, some of these microbes can cause a variety of illnesses in humans, the most common of which are gastro-enteric illnesses. As filter feeders, bivalves can also accumulate biotoxins if certain types of phytoplankton are present in the water column. These biotoxins will also cause illness. The biotoxins are not destroyed by cooking or other processing. There are, therefore, specific hygiene requirements in order to ensure the safety of bivalve molluscsThese ensure that the risks posed by microbiological contamination and biotoxins are reduced to an absolute minimum.

Classification of harvesting areas 

Controls are in place to improve the safety of bivalve molluscs intended for consumption. Shellfish business operators are responsible in ensuring that bivalve molluscs meet strict food safety standards before placing them on the market. The Food Standards Agency  classifies harvesting areas and production sites for England, Wales and Northern Ireland. Food Standards Scotland provides the classifications for Scottish sites.

Harvesting areas and production sites are classified on the basis of regular monitoring of E.coli levels in the bivalve mollusc flesh: 


E.coli concentration threshold 

Sampling, assessment and required treatment  


80% of sample results must be less than or equal to 230 E.coli per 100g flesh; AND no results may exceed 700 E.coli per 100g flesh using a five-tube, three dilution Most Probable Number (MPN) test 

Shellfish can be harvested for direct human consumption. 

  • minimum of 10 samples required per year 



90% of samples must be ≤4600 E.coli per 100g flesh; AND all samples must be less than 46000 E.coli per 100g flesh using a five-tube, three dilution Most Probable Number (MPN) test 

  • minimum of 8 samples required per year 

Shellfish can be supplied for human consumption after one of three processes: 

  • purification in an approved establishment 
  • relaying for at least one month in a classified Class A relaying area 
  • an EC approved heat treatment process 


≤46000 E.coli per 100g flesh using a five-tube using a three dilution Most Probable Number (MPN) test 

  • minimum of 8 samples required per year 

Shellfish can only be sold for human consumption after completing one of three possible processes: 

  • relaying for at least two months in an approved class B relaying area followed by treatment in an approved purification centre 
  • relaying for at least two months in an approved class A relaying area 
  • after an EC approved heat treatment process 


>46000 E.coli per 100g flesh using a three dilution Most Probable Number (MPN) test 

Shellfish from areas with consistently prohibited level results must not be subject to production or harvested. 

Our Classification of bivalve harvesting and production areas guidance note provides further details.

Viral considerations 

The most important viral hazards associated with the consumption of bivalve molluscs are Norovirus (NoV) and Hepatitis A virus (HAV), which are acquired from human faecal pollution of bivalve production areas. Viral outbreaks tend to be associated raw products. HAV infections rare in the UK, with occurrence usually associated with travel overseas. In contrast, NoV incidents can result in the temporary closure of bivalve production areas.  

NoV is one of the most common causes of gastroenteritis or stomach bugs, and is often referred to as the ‘winter vomiting bug’. The most common cause of transmission is person to person, although some cases occur via the food chain, either though the consumption of food contaminated at source or as a consequence of the foodstuff being contaminated in some way by a food handler during processing or serving. 

FSA has published have published a report Assessing the contribution made by the food chain to the burden of UK-acquired norovirus infectionThis provides an improved understanding of the contribution food makes to the transmission of NoV in the UK and how that might impact on overall rates of illness related to food. The main food borne transmission pathways were found to be: 

  • 63% - poor personal and food hygiene by handlers 
  • 34% - food borne transmission via salads and soft fruit (raw, ready-to-eat food)  
  • 3% - food borne transmission via raw oysters. 

Clearly this highlights the upmost importance of good personal and food hygiene practices.    

Seafish have created an Oysters and Norovirus guidance note.

Biotoxin requirements for delivering safer bivalve molluscs  

Controls are also in place to mitigate against potential biotoxin contamination of bivalve molluscs which comprise both testing oshellfish and also the monitoring the trends of certain phytoplankton species in the water column 

More details on the maximum permitted levels of biotoxins in shellfish are provided on our Marine Biotoxins page, as well in our an overview guidance sheet - Safer Shellfish: Biotoxin Monitoring.

We also have a series of industry guidance notes for fishermen and shellfish farmers on: 

Good Manufacturing Practice Guidelines 

Seafish has produced the Live Bivalves Workbook which provides a step by step guide to preparing bivalves for the marketThere is additional Seafish guidance on bivalve shellfish purification, Hazard Analysis Critical Control Point (HACCP) principles and on End Product Testing (EPT). 

Various Seafish-approved training opportunities are also available: 


On 31 December 2020 at the end of the UK-EU transition period, all directly applicable EU law in force became part of the body of domestic law in Great Britain (England, Wales, and Scotland). Under the terms of the Northern Ireland Protocol, the majority of EU food and feed hygiene and safety law (and any future amendments) continue to apply directly in Northern Ireland. The key European legislation for the production of live bivalve molluscs are: 

  • EC Regulation 2017/625  requires that Competent Authorities classify production and relay areas for live bivalve molluscs. This was previously applied through 882/2004.   
  • EC Regulation 853/2004 permits the commercial sale of bivalve shellfish from classified sites.  
  • EC Regulation 2019/627 specifies the rules for the official controls on products of animal origin including live bivalves; targeting relay and production areas for bivalve molluscs and the end product. These requirements ‘shall be without prejudice to food business operators' primary legal responsibility for ensuring food safety, as laid down in Regulation (EC) No 178/2002’. The requirements of 2019/627 were previously applied through EU Regulation 854/2004 
  • EU Regulation 2074/2005 lays down the methods for the determination of biotoxins.