Dissolved oxygen management is critical to fish welfare in aquaculture, with hypoxia causing acute distress, chronic health compromise, and mass mortality events when inadequately managed.
Oxygen management represents a case where welfare and productivity interests are closely aligned - fish dying from hypoxia are an economic loss as well as a welfare failure. However, chronic sublethal hypoxia below acute mortality thresholds causes ongoing welfare compromise that may not trigger an immediate economic response. Fish in moderately hypoxic water experience suppressed immune function, reduced growth, and behavioural changes consistent with distress. Climate warming is making oxygen management progressively more challenging in outdoor aquaculture systems, requiring investment in aeration infrastructure that some producers defer for cost reasons. Monitoring dissolved oxygen continuously rather than periodically is a minimum welfare standard that allows rapid response before welfare-critical thresholds are reached.