The question of whether fish experience pain has been debated for decades, but evidence has accumulated to the point where most animal welfare scientists and regulatory bodies now recognize fish as pain-capable animals.
Fish pain science has undergone a fundamental shift from the default assumption of no-pain-without-proof to recognition that the burden of proof should lie with those claiming fish do not experience pain. The evidence for fish nociception, opioid modulation, and pain-consistent behavior meets or exceeds the behavioral and physiological criteria we apply to infer pain in other non-verbal animals. The absence of a mammalian neocortex is not evidence against fish pain experience; rather, it suggests that conscious pain processing occurs through different neurological structures that evolution has converged toward similar functional outcomes. This scientific reorientation has practical implications for billions of fish killed annually in fishing and aquaculture with no welfare consideration, and is driving regulatory change in Europe and other jurisdictions to require fish welfare standards.