Mussels are filter feeders whose welfare status is uncertain but whose farming has relatively low environmental and welfare footprint compared to finfish.
The welfare status of mussels is genuinely uncertain — their nervous systems are simpler than those of crustaceans and fish, and current scientific evidence does not clearly support the existence of pain experience as understood in vertebrates. However, the precautionary principle suggests some attention to harvesting and processing methods even in the face of this uncertainty. Mussels that are alive at the point of cooking respond to thermal stimulus, though whether this constitutes a welfare-relevant experience remains debated. From a wider system perspective, mussel farming has among the lowest welfare footprints of any animal-derived food, requiring no feed and providing habitat for other species.