The evolutionary origins of fish pain have been studied to understand its biological significance and welfare implications. Understanding fish pain evolution helps assess the scope of aquatic welfare concern.
Fish pain evolution matters for welfare because the biological substrate of pain evolved before the fish-tetrapod split, meaning the basic machinery for pain processing is shared across vertebrates. Fish have nociceptors, opioid receptors, and neural pathways sufficient for pain processing. The ongoing debate is about the level of conscious experience - whether fish have the neural capacity for subjective experience of pain or only unconscious nociceptive reflexes. The current scientific consensus, including the Cambridge Declaration, accepts that the evidence warrants treating fish as capable of pain experience. This means billions of fish in commercial fisheries and aquaculture deserve welfare consideration that current practices rarely provide.