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.   Full explaination can be found here.     

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) Best Choice -  the most sustainably produced seafood.


Rating 2  (pale green)  Best 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 


For Wild Caught fisheries

The criteria against which MCS and Cornwall Good Seafood Guide measure wild capture fish sustainability are:


Stock or species status –the state of the stock i.e. stock size (the total weight of mature or breeding adults) and fishing pressure measured against recommended safe levels or reference points.

Where stock data are limited, the biological resilience of the species (based on its life history characteristics) is factored in to support what fishery information is available. Where the fishing pressure and biomass is completely unknown, the resilience of the species alone is used.


Management – an assessment of the measures, monitoring, surveillance and enforcement in place to ensure the stock is well maintained and the impacts of the fishery mitigated appropriately. Our assessment of management also includes consideration of whether the fishery is already certified as being sustainable by other bodies (such as the Marine Stewardship Council) and whether the fishery is in a Fisheries Improvement Project (FIP).


Capture method and ecological effects – an assessment of the impacts of the capture method on non-target species (bycatch), and wider ecosystem, and measures implemented to mitigate them. This includes whether the fishery is operating within a marine protected area (MPA), and is compatible or not with the Conservation Objectives, and legal requirements of the site.

For more details please download the full MCS good fish guide Wild Capture ratings methodolgy here 


For Farmed seafood  

The criteria against which MCS and Cornwall Good Seafood Guide measure farmed fish sustainability are:


Feed Sustainabilty– Traceability, sourcing and inclusion of both marine and non-marine feed ingredients.


Ecological effects – The impacts of production on: freshwater; habitats; water quality and other species both

indirectly and directly by reliance on juveniles.


Health and Welfare – Welfare standards, including slaughter and regional disease outbreaks.


Management – Planning, strategic assessment, regulation, enforcement and third party certification standards.


Download the full MCS Aquaculture Ratings Methodology here 


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 Cornwall Good 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 scores.


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.