Atlantic halibut (Hippoglossus hippoglossus) is one of the largest bony fish in the world and among the most commercially valuable aquaculture species. Its production is technically challenging due to specific larval rearing requirements, but the welfare considerations of established growout systems are increasingly well understood.
Biology and Behaviour
Atlantic halibut are benthic (bottom-dwelling) flatfish that lie on one side, with both eyes migrating to the upper surface during larval metamorphosis. They are ambush predators, consuming fish, crustaceans, and cephalopods. In nature they occupy deep, cold waters (200–700m) with temperatures of 4–10°C. Their benthic habit and preference for lying on solid substrate has specific implications for tank design in aquaculture.
Welfare Considerations in Production
- Tank design: Halibut require solid tank bottoms or mats to rest on; round tanks with smooth floors designed for salmonids are poorly suited to flatfish welfare needs
- Stocking density: As benthic fish, space allocation must consider floor area rather than water volume; crowding of flat fish at tank bottoms causes increased aggression and fin damage
- Light and visual environment: Halibut are light-sensitive and show preference for low light conditions; excessive light causes stress responses measurable by cortisol elevation
- Water temperature: Optimal growth occurs at 12–14°C; temperatures above 16°C cause significant thermal stress
- Feed delivery: As ambush predators, halibut respond better to feed delivered near tank bottoms; surface pellet delivery from automat feeders is less effective and creates feed competition
Slaughter Welfare
Percussive stunning followed by immediate spiking (ikejime or gill cut) is considered best practice for halibut. Electrical stunning is technically applicable but equipment design requires adjustment for flatfish morphology. Carbon dioxide and ice slurry immersion are common but less welfare-positive alternatives.
Disease Challenges
Viral and bacterial diseases — including vibriosis (Vibrio anguillarum), furunculosis (Aeromonas salmonicida), and halibut nodavirus — are significant welfare and production challenges. Vaccination programmes have reduced bacterial disease incidence. Good water quality, low stocking density, and genetic selection for disease resistance are primary prevention strategies.
Certification and Standards
ASC halibut certification is available and increasingly adopted by Norwegian producers. ASC standards address feeding, chemical use, disease management, and some welfare indicators. Further development of halibut-specific welfare indicators — analogous to the salmonid welfare indicators used in salmon farming — would strengthen welfare assurance in this premium species.