Farmed fish welfare should plausibly be one of the effective animal advocacy community’s priorities because of the current neglectedness of the issue, the likelihood that farmed fish suffering is large in scale, and the potential tractability of interventions to improve farmed fish welfare.1 With this in mind, ACE would like to reduce uncertainty about the impact of corporate campaigns aimed at improving farmed fish welfare.2 We hope that our new report will help us move toward that goal.

We’ve researched various considerations relevant to determining appropriate indicators of farmed fish welfare. Our report also discusses potential reforms to improve the welfare of farmed fishes. Following that, it outlines key resources and questions for further consideration. The appendix provides some further information about farmed fish production, our literature search, and our approach to analyzing the literature.

Our conclusions are quite tentative, as further research needs to be done to determine the best indicators of fish welfare as well as the most effective interventions for helping fishes. Generally, we find that the initial effects of changing common slaughter methods from asphyxia and live chilling to properly applied electrical or percussive stunning seem promising. The initial effects of improving dissolved oxygen levels seem promising as well. An initial survey of the evidence also seems to support the welfare benefits of opposing triploidy, at least for Atlantic salmon.

There are a few interventions that we currently feel are less promising because the evidence supporting them is mixed or lacking. These include (i) environmental enrichment and (ii) some methods for reducing the number of wild-caught fishes used in farmed fish feed. For environmental enrichment, further research may help us identify promising interventions. On the other hand, the effect of reducing the amount of wild-caught fishes in feed seems fraught with large degrees of uncertainty. Further, when advocating for switching a carnivorous species to plant-based feed or farming an herbivorous species instead of a carnivorous species, it’s worth considering the average survival rates, weight at slaughter, and lifespan of different farmed fish species.

We hope that further research will decrease our uncertainty about the following promising interventions:

The use of anaesthesia to reduce stress at time of slaughter

The use of sedatives during transport

Minimizing of prolonged handling of fishes, especially out of water

Water quality parameters other than dissolved oxygen

Farmed fish genetics

Stocking density

We also hope to develop a stronger understanding of the other factors that affect the promise of farmed fish interventions, including the relevant economic considerations and the ethology of the most numerous farmed fish species. We encourage further discussion and analysis of promising farmed fish welfare interventions.

There are many questions—some of which are listed below—that could cause us to significantly update our views.

In the current farming systems, do some of the most numerous farmed fish species have significantly different welfare levels than others?

How promising are the welfare indicators that we didn’t consider (e.g., indicators regarding the presence of various pathogens and parasites, indicators regarding injuries and physical deformities, genetic indicators, and indicators derived from preference tests)?

How promising are the interventions that we didn’t consider (e.g., stocking density, use of sedatives, and water quality parameters other than dissolved oxygen)?

What are the humane slaughter parameters for some of the most numerous farmed fishes such as crucian carp, silver carp, and grass carp?

Are there better, yet still feasible, methods other than electrical and percussive stunning for reducing pain and distress before slaughter?

What are the optimal dissolved oxygen parameters for some of the most numerous farmed fishes such as crucian carp, silver carp, and grass carp?

For more information, read our full report.