How our Good Fish Guide ratings work

The updated Good Fish Guide Wild-capture Methodology is now open for consultation.

This methodology explains how we assess wild-capture fisheries and develop our ratings. To help ensure the methodology is robust, credible and informed by the best available evidence, we are inviting feedback from anyone with relevant technical knowledge or insight.

To share comments or supporting information, please email ratings@mcsuk.org by 13 May 2026.

After the consultation closes, we will review all feedback before finalising the methodology.

We create one rating for each species farmed by a specific method in a specific area. We rate four different things: fish feed, environmental impact, fish welfare, and management.

Fish feed

This is really important. Most farmed fish, except shellfish, need to be fed. Carnivorous species, like salmon and some prawns, are often fed fish that have been caught in the wild. If these ‘feed fisheries’ are not well managed, this can be a threat to wild populations. As part of their diet, some fish are fed soy or palm oil, which is also sometimes produced unsustainably.

Where fish feed comes from, what goes into it, how sustainable the ingredients are and how much food is needed are all things we look at when assessing the feed section.

Environmental impacts and interactions

Different methods of farming fish can have a range of different impacts. What might be a concern for some fish, such as freshwater use in warm-water prawn farming, might not be a concern for others, such as fish farmed in the sea. In this section, we look at a whole host of impacts – from disease and parasites to chemical use and escapes. These are the most important aspects of environmental impact, regardless of what country or what fish we are looking at.

Fish welfare

Welfare is an important issue for all farmed animals, and fish are no different. Good welfare standards mean fish are healthy, happy and stress-free. They also indicate good farm management. We look at what regulations and practices are in place to ensure this.

Regulation and management

All fish farms are managed and every country has their own regulations for the industry. Some of these are very good, others less so. It’s important that the regulations are comprehensive and, most importantly, enforced. We also look to see if the farmed fish is independently certified as being responsibly farmed.

We create one rating for each fishery. A fishery is a species of fish or shellfish from a specific area caught in a specific way. There are three main things we look at: stock status, management, and capture (or fishing) method impacts.

Stock status

The size and health of a fish population, or ‘stock’, that is being targeted by fishermen is a crucial indicator of whether a fishery is sustainable. If the stock is too small to withstand fishing, it's at risk of crashing.

We use publicly available stock assessments created by fishery scientists whenever they’re available. It’s a very complex area to assess. There are two aspects to review:

• The size of the stock: Is it big enough to keep reproducing? If it’s below safe levels, it’s considered to be overfished.
• The level of fishing pressure: Are more individual fish being fished from the stock than can naturally be replaced? If fishing pressure is too high, the stock is subject to overfishing.

The target level many fisheries aim for is 'maximum sustainable yield' – this is the most fish that can be caught year after year while keeping the population at a healthy size.

Management

Good management is vital to be sure fishing doesn’t cause fish populations to decline. A well-managed fishery should have laws that are:

• Appropriate: Regulations should follow scientific recommendations, including catch limits, closed seasons, or closed areas.
• Enforced: Managers should make sure fishing boats follow the regulations by monitoring them, and issuing penalties or bans to fishermen that break the rules.
• Effective: The stock should not be overfished or subject to overfishing.

Capture method

The environmental impacts of fishing vary hugely, depending on the method used and where it's happening. We consider three aspects of how the fish are caught:

1. Habitat damage: Does the fishing method come into contact with the seabed? Is it happening in a Marine Protected Area? If so, how severe might any damage be? For example, both potting and dredging touch the seabed, but dredging tends to have a much bigger impact.
2. Bycatch: Is the fishery is catching other species by accident? For example, fishermen catching haddock may also catch cod, and, in some areas, this could result in cod populations shrinking.
3. Vulnerable species: Could the fishery be affecting endangered, threatened or protected species? Animals such as sharks, dolphins, turtles and seabirds are often caught or otherwise affected by fishing. Some of these species are at risk of extinction, and pressure from fishing could increase those risks.

If there is a certification in place for a fishery or farmed species, for example by the Marine Stewardship Council or Aquaculture Stewardship Council, this can improve the scores we give. Certifications sometimes, but not always, get better scores because they are being closely monitored and must meet certain standards. Some of our ratings may seem to cover the same fishery or farmed species, but have different scores because one rating is for the certified component, and the other is for the uncertified component.

Sometimes, fishery improvement projects (FIPs) or aquaculture improvement projects (AIPs) are in place to tackle major issues, like significant environmental impacts or a lack of important data. AIPs aren’t that common yet, but they’re growing. FIPs are more common. They are a collaboration between fishers, businesses and regulators.

FIPs and AIPs are usually set up for fisheries or farming systems that are not currently very sustainable and might be getting a 5 (red) rating in the Good Fish Guide. If we think the project is going in the right direction, we may give it an Improver rating. In this case, we don't tell people or businesses to Avoid buying it, because we think it’s better to invest in improving poorly-performing fisheries or farming systems than abandoning them altogether. However, it won’t be considered sustainable until the project has successfully addressed all the key issues.