Pangasius catfish, sold as swai or basa, are farmed in Vietnam in high-density ponds with water quality issues that cause chronic respiratory and parasitic disease.
The ability of pangasius to breathe atmospheric air allows them to survive in oxygen-depleted water that would kill most fish, but this tolerance masks welfare problems rather than eliminating them. Fish in low-oxygen water experience chronic physiological stress even without acute mortality. High stocking densities cause aggression, chronic fin damage, and disease pressure requiring prophylactic antibiotic use. The environmental conditions in many pangasius farms fall significantly below what welfare science would consider adequate for fish wellbeing.