A new science of suffering is revealing that fish feel pain in ways we can no longer deny.
Groundbreaking research is challenging centuries of assumptions about aquatic animals
For centuries, fish have been dismissed as simple creatures with fleeting memories and primitive nervous systems. The question "Do fish feel pain?" has often been met with skepticism. Yet, a scientific revolution is underway, challenging these long-held assumptions and forcing us to reconsider our relationship with these aquatic animals.
Groundbreaking research published in 2025 has moved beyond philosophical debates to provide startling quantitative evidence of fish suffering. By applying innovative measurement frameworks to common fishing practices, scientists have documented the intense, prolonged pain fish experience during slaughter. This research doesn't just suggest fish feel pain—it measures it in minutes of verifiable suffering, creating an urgent moral and scientific imperative to rethink how we treat these animals 1 .
The question of fish pain has divided scientists for decades
Some researchers, including scientists like Brian Key and JD Rose, argue that fish lack the neural architecture required for conscious pain experience 7 . Their position emphasizes that:
On the other side of the debate, researchers like Lynne Sneddon and Victoria Braithwaite have assembled compelling evidence for fish sentience 7 . Their work demonstrates that:
"From an ethical and moral perspective, a best practice is to go with the thought that fish (and other animals) can and do feel pain and do what you can to minimize their discomfort" 7 .
The WFF measures welfare impact through a fundamental metric: cumulative time spent in different affective states 3 . Similar to how environmental footprints quantify ecological impact or disability-adjusted life years measure human health burdens, the WFF provides:
Dr. Wladimir Alonso, who helped conceptualize 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" 2 .
Aquatic Animals
Livestock
Landmark 2025 study reveals the suffering during common slaughter methods
In a landmark 2025 study published in Scientific Reports, researchers applied the WFF to one of the most common slaughter methods in commercial fishing: air asphyxia 3 . The study focused on rainbow trout, a globally farmed species often killed by removal from water.
The research team conducted a comprehensive review of existing studies on stress responses during asphyxiation, analyzing behavioral, neurophysiological, and pharmacological indicators 3 . They divided the asphyxiation process into four distinct phases:
Triggering immediate neurochemical stress responses
CO2 accumulation causing blood acidification
Energy reserves depleted while struggling
Final progression toward unconsciousness
Using EEG measurements and behavioral observation, researchers pinpointed when fish lost consciousness and documented the physiological markers of distress throughout each phase 8 .
The findings were striking. Rainbow trout endured an average of 10 minutes of moderate to intense pain during air asphyxia, with some fish suffering for up to 22 minutes before losing consciousness 1 3 . When standardized by production output, this translated to approximately 24 minutes of pain per kilogram of fish 3 .
| Metric | Average | Range | Context |
|---|---|---|---|
| Per fish | 10 minutes | 2-22 minutes | Larger fish suffer longer |
| Per kilogram | 24 minutes | 3.5-74 minutes | Varies by conditions |
| Initial intense pain | 5 seconds | Immediate response | Neurochemical stress onset |
The suffering begins almost instantly. Just five seconds of air exposure triggers a neurochemical response associated with negative emotions 1 . Fish demonstrate vigorous twisting and turning—clear aversion behaviors—as their gill structures collapse and CO2 accumulates, acidifying their blood and cerebrospinal fluid 1 .
| Stage | Primary Physiological Event | Behavioral Manifestation |
|---|---|---|
| Initial exposure | Gill collapse, oxygen deprivation | Vigorous struggling, gasping |
| Early asphyxiation | CO2 accumulation, blood acidification | Increased respiration attempts |
| Mid-phase | Metabolic exhaustion | Reduced movement, continued gasping |
| Late phase | Neuronal depression | Loss of consciousness |
Understanding how researchers study fish pain reveals the sophistication of this field
| Tool/Method | Function | Example Application |
|---|---|---|
| Nociceptor mapping | Identify pain receptor distribution | Found in heads and faces of bony fish 7 |
| Opioid administration | Test pain/pleasure mechanisms | Butterflyfish sought cleaning sites more after opioid mimics 9 |
| EEG measurements | Monitor brain activity | Determined consciousness duration during asphyxiation 8 |
| Behavioral analysis | Document response to stimuli | Recorded twisting, gasping during air exposure 1 |
| Pharmacological blocks | Confirm pain receptor function | Naloxone reduced cleaning preference in butterflyfish 9 |
Examining brain activity and nerve responses to stimuli
Using drugs to understand pain and pleasure mechanisms
Documenting responses to potentially painful situations
Recent research has expanded beyond negative experiences to investigate whether fish can feel pleasure
A 2025 study published in Proceedings of the Royal Society B examined cleaner fish and their clients on coral reefs 9 .
The research found that threadfin butterflyfish—even when parasite-free—actively sought out being cleaned by bluestreak cleaner wrasse, suggesting the experience might be pleasurable 9 .
When researchers administered opioid-mimicking drugs, the fish spent more time seeking cleaning stations, while opioid blockers reduced this interest 9 . This indicates fish may have complex emotional lives including positive states, not just pain avoidance.
Fish may experience positive emotional states, not just pain avoidance
The evidence for fish sentience has profound implications for fishing practices, aquaculture, and animal welfare regulations
With an estimated 1.1-2.2 trillion wild fish and 78-171 billion farmed fish killed annually, the scale of potential suffering is staggering 3 .
Research indicates that more humane slaughter methods like electrical stunning could avert significant suffering. The 2025 study found that proper electrical stunning could save 60-1,200 minutes of moderate to extreme pain for every US dollar of capital cost 2 .
Percussive stunning also shows promise, though consistent application in commercial settings remains challenging 3 .
The growing scientific consensus demands a shift in how we view and treat fish. As the research continues to develop, the question is increasingly becoming not whether fish feel pain, but how we can minimize the suffering we cause them. The same scientific tools that have quantified their pain may now help us develop more compassionate practices.
"Societal concern about the impacts of production practices on animal welfare is rising, as evidenced by consumer-driven movements, labelling efforts, accreditation schemes, policies and legislation that prioritize animal welfare" 3 .
The science has spoken—we can no longer rule out fish pain. The question now is what we choose to do about it.