Simple SummaryEvery year an estimated 1.5–2.7 billion wild fish are caught by UK commercial sea fishing fleets subjecting most to severe stressors. Scientific research shows that fish are sentient beings, but UK animal welfare laws do not protect commercially caught wild fish. For example, stunning fish before slaughter is rare and gutting them alive is a common practice. There are therefore major welfare issues in wild capture sea fisheries, no laws to protect the welfare of wild fish at sea, and great potential to reform practice to improve the lives of billions of sentient fish. The article investigates this through reporting findings from interviews with 18 experts with a stake in wild fish welfare. The article reviews the UK fishing industry, policy context and scientific evidence that fish are sentient, linked to stakeholder views about what fish experience during wild capture. The article then analyses industry practices, resultant welfare harms and stakeholder attitudes towards them. No participant disputed that fish are sentient and all were able to identify key stressors to fish in different stages of the capture process, together with potential mitigations. Interviews revealed that harms can be worsened by their hidden nature along with conservative industry attitudes towards brutal practices which would be unacceptable in other areas of animal food production. The article raises awareness of an under-researched welfare problem in UK wild capture sea fisheries but should have wider significance to many fishing nations.An estimated 1.5–2.7 billion wild fish are caught by UK commercial sea fishing fleets annually. Most are subjected to severe stressors during capture; stunning is rare and gutting alive is common practice. Fish are recognised in UK law as sentient beings, but commercially caught wild fish are excluded from welfare protections. Animal welfare impacts in wild capture sea fisheries are therefore on a massive scale, with major potential for legislative and market-based reforms. Interviews were conducted with 18 experts working within the fishing and seafood industry, fisheries management, scientific research and animal/fish advocacy organisations. The findings reveal a significant welfare gap between societally acceptable ways to treat sentient animals and the reality of capture fisheries. The participants pointed to harms caused to fish throughout different stages of the capture process caused by combinations of variables from fishing gear and methods to biological, environmental and other factors, noting that all require mitigation. Interviews revealed that the nature of harms may be exacerbated by conservative attitudes towards brutal practices in the industry, driven by profit and efficiency and free from legal restraint. To address the welfare gap, stakeholders favour engagement with the industry to improve understanding of harms and to identify mutually beneficial and shared objectives through alleviating stressors to fish in the capture process. This empirical research is focused on UK wild capture sea fisheries. However, given the dearth of welfare legislation globally, it has significance for fishing nations and the many billions of wild sea fish captured each year around the world.