Farmed fish - key welfare issues

Water quality

The 'quality' of water (temperature, pH, oxygen levels, etc.) 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 if too high may impact on fish welfare. Similarly, increasing the water temperature when the fish are small can make them grow more quickly, but if fish grow too fast during this time it can result in spinal deformities.

Handling procedures

Farmed fish are sometimes handled, for example, when they are being vaccinated or when they are being graded according to their size. These procedures can be stressful for the fish, for example if they are taken out of the water, and it is 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 is not necessarily one of the most important things affecting fish welfare. Some fish seem to prefer a higher stocking density, while others prefer lower stocking densities. Stocking densities that are too low can cause certain species of fish to become territorial and aggressive towards each other.


Well boat transporting farmed salmon © RSPCA Farm Animals Department

All transport, whether by road, boat or helicopter, can be potentially stressful for the fish, so extra attention is needed during transport, particularly when the fish are loaded and unloaded. It is 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.


A number of slaughter methods are 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 which is 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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