Pangasius catfish tolerate low dissolved oxygen through accessory air-breathing but this tolerance is exploited in intensive production to maintain welfare-compromising densities that still achieve acceptable survival rates.
Pangasius welfare illustrates how physiological tolerance can be conflated with welfare adequacy. Because pangasius can survive conditions that would rapidly kill salmon — extreme low oxygen, high ammonia, severe crowding — the industry has historically used survival rates as a proxy for acceptable welfare. But survival is not welfare: pangasius that survive extreme density experience chronic behavioral suppression, immune compromise, and physiological stress that constitutes genuine welfare harm even in animals that ultimately survive to slaughter. Their air-breathing adaptation was selected to allow survival of temporary drought conditions in Southeast Asian rivers — not to enable permanent extreme crowding in commercial ponds. Welfare-informed density standards for pangasius should be based on behavioral and physiological welfare indicators rather than mortality thresholds, and the precautionary evidence suggests that current intensive densities substantially exceed welfare-compatible levels.