Lampreys are ancient jawless fish whose declining populations signal broader river ecosystem degradation, and whose welfare deserves consideration given evidence of pain processing in vertebrates.
Lampreys are often overlooked in welfare discussions due to their ancient lineage and unfamiliar body plan, but as vertebrates they possess the neurological structures associated with pain processing in other fish species. Whether they experience suffering is uncertain, but the precautionary principle supports consideration. More immediately, lamprey declines signal broader river ecosystem degradation that harms many unambiguously sentient species. Restoring lamprey populations by removing river barriers, reducing water pollution, and improving spawning habitat benefits entire river ecosystems. The larvae play critical roles in processing organic matter and creating habitat conditions that support salmon, trout, and other river species whose welfare is better established.