Bivalves (oysters, mussels, clams, and scallops) are farmed at enormous scale, and their welfare status remains scientifically contested with important ethical implications.
Bivalve welfare sits at the most philosophically contested region of animal ethics. The scientific case for significant sentience in oysters and mussels is weak — they lack the neural architecture considered necessary for suffering. However, certainty is not achievable, and the scale of bivalve consumption (hundreds of billions annually) means even small probabilities of experience matter enormously. Scallops, with their more complex nervous systems and dramatic escape responses, deserve more precautionary consideration. For those reducing animal product consumption for welfare reasons, bivalves are often considered the most ethically unproblematic animal food option.