[Disclosure: I was the lead author of this report and previously worked at ACE]
A brief summary of the report;
This report notes that according to the INT framework, improving farmed fish welfare seems to score highly and plausibly ought be a priority for the animal advocacy community.
The report then assesses different indicators of fish welfare and includes a literature review and an overview of the methodology. It also includes recommendations for promising reforms, and some clarification of pressing research questions still outstanding.
Shifting away from slaughter by asphyxia and live chilling to correctly used electrical or percussive stunning appears promising. The same can be said for boosting dissolved oxygen levels in the water that fish are kept in. For Atlantic salmon in particular, opposing triploidy seems beneficial. This may or may not be cross applicable to other fish.
Mixed or lacking evidence allows for significantly lower confidence in environmental enrichment and certain methods for reducing the number of wild fish added to farmed fish feed. While environmental enrichment may look more promising after additional research, the effect of changes to farmed fish feed faces a large amount of uncertainty. Transitioning a carnivorous species to a plant-based feed requires investigation into how that may impact average survival rates, weight at the time of slaughter, the amount time fish spend on a farm, and the degree to which supply of wild-caught fish is responsive to changes in demand.
Interventions that would still require further research to assess their potential include:
- Anaesthesia for reducing stress during slaughter
- Use of sedatives during transport
- Minimizing the handling of fish, particularly out of water
- Water quality parameters other than dissolved oxygen
- Decreasing stocking density
The report also highlights a need for a stronger understanding of relevant economic considerations and the ethology of the most numerous farmed fish species.