How We Rate Fish

Cornwall Good Seafood Guide has been developed to provide the public with a trusted and up to date summary of the sustainability of all of Cornwall’s fisheries. Every species of commercial value that is landed by Cornish fishermen to Cornish ports is featured in this website. This  guide draws together all available information into one place to enable consumers and business to make their own well informed choice when choosing Cornish seafood.



For species that you may see offered for sale that are not from Cornwall, click here to visit the Marine Conservation  Society, Good Fish Guide website.

Some species that may be caught are prohibited and can’t be sold. For a list of these species click here.



To ensure that our ratings are comparable we use the internationally recognised methodology devised by the Marine Conservation Society (MCS).

The MCS Methodology uses a range of sustainability ratings from 1 (best) to 5  (worst) to rate both wild-caught and farmed fish.       

To make the complex subject of fish sustainability easier to understand a rating is produced for wild-caught fish based on the sustainability of the stock in it’s capture area, sub-area, it’s management and the fishing method used to catch it. Each is scored against sustainability criteria to produce a rating.  For example for this website we focus on Capture area FAO 27; Sub area Cornwall; and management within or outside our 6 mile limit.

The sustainability of farmed fish is based upon the source ; sustainability and amount of feed used; the impact of its production on the environment and how it is managed and regulated. 

Fish, wild-caught or farmed, rated 1 and 2 are listed as MCS Fish to Eat and those rated 5 are listed as MCS Fish to Avoid. Fish rated 1 to 3 are recommended by the Cornwall Good Seafood Guide, and can be marketed using our 'recommended' logo.


Rating 1 (dark green) is associated with the most sustainably produced seafood.


Rating 2  (pale green) is still a good choice, although some aspects of its production or management could be improved.


Rating 3  (yellow) should probably not be considered entirely sustainable at this time. Marine Conservation Society recommend that you eat 3-rated fish only occasionally and check this website for specific details.


Rating 4  (orange) These fisheries are some way from being sustainable at this time. The fisheries or farming methods are likely to have a number of significant environmental issues or uncertainties associated with their production. We recommend that you eat these fish only very occasionally, and ideally seek alternatives where you can. We would like to see improvements made to these fisheries which address the specific issues of concern.


Rating 5 (red) is associated with fish to be avoided.


Scored factors 

The criteria against which MCS measure wild capture fish sustainability are:


Stock or species status – state of the stock (the total weight of mature or breeding adults) against recommended safe levels and levels of exploitation. If a fish population is healthy with a large population of reproductive fish and a good number of new fish growing each year then a larger number of fish can be removed each year by fishermen, without risk of the population falling. Healthy stocks mean more productive fisheries. Over-fished stocks are far more vulnerable and produce far smaller yields of fish for fishermen. Where insufficient scientifc data is available to asses stock status the biological vulnerability to fishing of that species is used to asses the risk posed by fishing on that stock.  The Fishbase vulnerability score out of 100 is used to score this 


Management – an assessment of the checks and enforcement measures in place to ensure the stock is well maintained and the impacts of the fishery are mitigated against appropriately.


Capture method and ecological effects – an assessment of the impacts of the capture method on the target species, non-target species and wider ecosystem.  Not all fishing methods are equal. Some have greater impact on the stocks they target and on the wider environment than others.  All fisheries are scored on their individual merits, and improvements made by fishermen that reduce impacts and improve selectivity are reflected in better scores.



The criteria against which MCS measure farmed fish sustainability are:


Feed – The source; traceability; sustainability and amount of feed used to produce the fish


Ecological effects – The impact that the production system has on the surrounding environment, habitats and species.


Health and Welfare – The health and welfare of the farmed fish including diseases


Management – How farms are managed and regulated and how effective these are


Certification – if a farm is certified to credible production standards such as Aquaculture Stewardship Council(ASC)



Information for the above criteria for all Cornish fisheries have been carefully compiled by Cornwall Wildlife Trust. The ratings are reviewed periodically by an Independent Advisory Board which includes fishermen (and their representatives), fish merchants, restaurateurs, Cornwall Inshore Fisheries and Conservation Authority (CIFCA), and the Marine Conservation Society (MCS).


The CWT Seafood Guide project serves to help develop the regional aspect of MCS FishOnline and provides ratings specific to  Cornwall to highlight information and research affecting it’s shores.


We hope that this will create more local appreciation for Cornwall’s fishing industry and the improvements being made to safeguard the future of fish stocks and our marine ecosystem.


The methodologies have been developed by the Marine Conservation Society to help consumers identify the most environmentally sustainable fish and make more informed buying decisions.


For more information you may wish to read the MCS Wild-CaptureMethodology Handbook and the MCS Aquaculture Methodology Handbook.