Atlantic halibut is the largest farmed flatfish, with significant welfare challenges around metamorphosis, light sensitivity, handling stress, and slaughter in cold North Atlantic aquaculture systems.
Atlantic halibut present unique welfare challenges compared to round fish like salmon. Their flatfish body plan means crowding stress is expressed differently — halibut pile on top of each other rather than distributing volumetrically, causing crushing and hypoxia in lower layers. Handling during grading causes acute stress and physical injury to their sensitive skin and scales. Light management during the juvenile metamorphosis phase is critical for normal development — inappropriate lighting causes abnormal eye migration and skeletal deformity. Slaughter welfare is particularly concerning: ice slurry chilling takes significantly longer to induce unconsciousness in halibut than in smaller species, and the thick musculature resists temperature change. Electrical stunning or percussion before chilling is feasible and represents a meaningful welfare improvement. Norwegian welfare regulations are among the most advanced globally for flatfish and provide a model for other producers.