New study quantifies fish slaughter pain and cost-effectiveness of welfare solutions

June 5, 2025 – A new study in Scientific Reports reveals the hidden pain of fish during slaughter and offers practical solutions to improve their welfare. Focusing on rainbow trout, the research quantifies pain in air asphyxia—a common slaughter method—using the innovative Welfare Footprint Framework (WFF). With up to 2.2 trillion wild and 171 billion farmed fish killed annually, the findings highlight an opportunity for welfare reforms on a massive scale.

The study shows rainbow trout endure an average of 10 minutes of intense pain during air asphyxia, with estimates ranging from 2 to 22 minutes depending on factors like fish size and water temperature. This translates to approximately 24 minutes of pain per kilogram of fish. These estimates are based on a comprehensive review of existing research to assess the intensity and duration of pain and distress experienced by the fish. 

Crucially, the study also assesses the cost-effectiveness of interventions. If implemented properly, electrical stunning could avert 60 to 1,200 minutes of moderate to extreme pain for every U.S. dollar of capital cost. Percussive stunning  offers high welfare potential as well, though challenges remain in achieving consistency in commercial settings. The study also notes that pre-slaughter practices such as crowding and transport – often overlooked – are likely to even cause greater cumulative suffering than the slaughter itself. 

At the heart of this study is the Welfare Footprint Framework (WFF), developed by the Center for Welfare Metrics, a novel method that quantifies animal welfare by estimating the total time animals spend in various states of suffering or well-being. By assigning time-based values to subjective experiences, the WFF allows for direct comparisons between different animal welfare interventions, much like environmental footprints or health impact assessments in human contexts, in familiar terms that anyone can understand.

Dr. Wladimir Alonso, who conceptualized the method, explains, "The Welfare Footprint Framework provides a rigorous and transparent evidence-based approach to measuring animal welfare, and enables informed decisions about where to allocate resources for the greatest impact." 

This study’s results could help shape regulatory discussions, improve certification standards, and guide welfare investments that deliver the greatest benefit per dollar spent. 

Publication: Schuck-Paim et al. (2025). Quantifying the welfare impact of air asphyxia in rainbow trout slaughter for policy and practice. Scientific Reports. DOI: 10.1038/s41598-025-04272-1

For more information: media@welfarefootprint.org.

The Welfare Footprint Framework is freely available for research and policy use at welfarefootprint.org.