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Key issues surrounding the welfare of farmed fish

Here are some of the key issues surrounding the welfare of farmed fish in the UK.

Water quality

The quality of water (its temperature, pH, oxygen levels, and so on) has a big impact on fish welfare. Different fish species survive better in different conditions. 

  • We believe more work is needed on aspects of water quality such as carbon dioxide levels, which can impact fish welfare if they're too high.
  • Increasing the water temperature when the fish are small can make them grow more quickly, but if fish grow too fast during this time they can end up with spinal deformities.

Handling procedures

Farmed fish are sometimes handled, for example when they're being vaccinated or graded according to their size. These procedures can be stressful for the fish, especially if they're taken out of the water, and it's essential to keep handling to an absolute minimum.

Stocking densities

Stocking density is the weight of fish kept in a given volume of water. Research and practical experience has shown that, on its own, stocking density isn't necessarily one of the most important things affecting fish welfare. 

  • Some fish seem to prefer a higher stocking density, while others prefer them to be lower. 
  • Stocking densities that are too low can cause certain species of fish to become territorial and aggressive towards each other.


All transport, whether by road, boat or helicopter, can be potentially stressful for the fish.

  • Extra attention is needed during transport, particularly when the fish are loaded and unloaded. 
  • It's also essential to be able to maintain the correct water quality for the whole length of the journey, even if delays or emergencies make the journey much longer than expected.
boat transporting farmed salmon © RSPCA


There are a number of slaughter methods used in aquaculture. 

  • Methods such as the use of carbon dioxide, suffocation in air or on ice, or bleeding the fish without stunning are all unacceptable on animal welfare grounds. 
  • We believe that the only method of slaughter that's acceptable in terms of animal welfare is percussive stunning followed by bleeding.

Find out how you can help improve the welfare of farmed fish.

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