Oyster, Pacific, oysters (Farmed)

Crassostrea gigas

Method of production — Farmed
Production country — UK
Production method — Bottom & suspension culture
Picture of Oyster, Pacific, oysters (Farmed)

Sustainability rating one info

Sustainability overview

Updated: September 2019.

Pacific oysters farmed in the UK in suspended culture and bottom culture have some environmental impact and do not require any commercial feed sources as they get all their nutrient requirements from the surrounding water. Oyster aquaculture is entirely sea-based and habitat concerns are minimal. Recent oyster culture generally does not involve the use of chemicals and there is no concern about the impact of effluents. Juveniles are hatchery-based. Disease risk and parasite interactions are thought to be minimal and do not threaten regional level operations. However, there has been problems with escapes of Pacific oyster and there is concern that there will be an increase in wild populations with an increase in seawater temperature. Environmental regulations are in place and are largely effective, however, there is no independent certification available.

Feed Resources

Criterion Score: 5 info

Farmed oysters do not require any commercial feed sources as they get all of their nutrient requirements from the surrounding water. They feed by filtering mainly microscopic algae (phytoplankton), but also some organic detritus in sea water.

Environmental Impacts

Criterion Score: 4 info

Overall, Pacific Oyster aquaculture has some environmental impacts. Oysters are found in marine and brackish water and therefore culture is entirely sea-based and does not deplete freshwater supplies. Habitat concerns resulting from the physical infrastructure associated with on-bottom oyster culture include the alteration of hydrodynamics and current velocities, as well as reduced flow rates. However, the positive impacts of oyster beds through the provision of hard substrate through the provision of hard substrate for recruitment and refuge, outweigh the risks associated with increased sedimentation. Oysters growing in suspended culture also create favourable structures and habitats for other invertebrates and fishes.

Recent oyster culture generally does not entail the application of chemicals (i.e. antibiotics, pesticides, herbicides, fertilizers) to control fouling and predators or to prevent disease. Furthermore, the water in which chemicals would be used generally is not released to the marine environment. There is no evidence that discharges from oyster culture cause or contribute to cumulative impacts beyond the immediate vicinity of the farm. Furthermore, oyster farming may provide increased benefits through their extractive nature when cultured with other species.

Juveniles are supplied by hatcheries. Extensive research has not revealed any information about parasitic transfer of Pacific Oysters to Native Oyster populations, although this is not thought to be an issue. Disease outbreaks can and do occur, although they do not threaten regional level populations. There is also evidence of escapes and small fisheries have developed with the naturalization of the species. Presently, saltwater temperature is thought to limit the range and density of wild Pacific oysters in cooler temperature regions. However, with sea temperatures rising, they are now becoming more widespread. It is highly likely that they will continue to spread northwards throughout mainland Britain as a consequence. A variety of oyster predators exist among oyster farms, including echinoderms, snails, crabs, fishes and seabirds. A variety of methods are employed to reduce predation but there are no direct negative impacts on predatory species.

Fish Health and Welfare

Criterion Score: 1 info

Animal welfare is not applicable for shellfish as it is not covered by EU regulations on welfare. Humane slaughter has been carried out by RSPCA definitions.


Criterion Score: 2 info

Aquaculture policy in the UK is a devolved matter, with the separate administrations of Wales, England, Northern Ireland and Scotland responsible for its collective oversight. In England, the Marine Management Organisation is preparing marine plans for 11 predefined areas in England. The first of these plans were published in 2014 and all plans are due to be in place by 2021. Aquaculture production in Scotland is covered in the 2015 Scottish National Marine Plan and in Wales by the 2019 Welsh National Marine Plan. The Northern Ireland Marine Plan will come into effect by 2021.

In the UK, regulations regarding the environmental impacts of aquaculture are in place. This includes the Habitats Directive 92/43/EEC and the Birds Directive 2009/147/EC, which form the cornerstones of the EU’s nature conservation policy and protect valuable habitats and species. There is also regulation in place to cover the use of land and water resources, discharges including effluents and their impacts, disease management and biosecurity.

However, while regulation exists on species introduction, Defra are yet to declare a position on whether Pacific oysters are invasive or naturalised. Therefore, regulations are marked as being only partially effective. In the UK, there is currently no third party certification for Pacific oysters.

Production method

Bottom & suspension culture

Oysters are bred in hatcheries and then grown on in the sea - usually in semi-rigid plastic mesh bags, supported by steel trestles secured in intertidal waters. They can also be grown in suspended mesh nets.


Oysters belong to the commercially important group of bivalve molluscs which also includes mussels, clams and cockles. The Pacific oyster, now widely distributed, originated in north-eastern Asia. Pacific oysters, as with many oyster species, develop first as males, spawn, and then later develop into females. Spawning occurs in the summer.


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