Lampreys are ancient jawless fish that play important ecological roles in river systems, with welfare considerations emerging as fish sentience science advances.
Lamprey welfare sits at the frontier of fish sentience science, complicated by their phylogenetically ancient nervous system that predates the evolutionary developments associated with pain processing in more derived fish. Lampreys lack a true vertebral column (they have a notochord) and their neural architecture differs fundamentally from that of teleost fish. Whether lampreys experience pain in a morally relevant sense is genuinely uncertain - they show nociceptive responses to tissue damage but the subjective experience associated with these responses is unknown. Their ecological importance, however, is clear and provides conservation motivation regardless of welfare uncertainty. Adult sea and river lampreys feed parasitically on fish during marine phases, then return to freshwater to spawn and die, providing nutrient inputs that benefit river ecosystems. Their larvae filter-feed on organic matter in river sediment, cleaning the water. River restoration that removes barriers to lamprey passage benefits both lamprey populations and the ecosystem services they provide. As fish sentience science advances, more specific welfare guidance for lampreys may become possible.