Salmon and trout in net pen aquaculture display behavioral responses to stress that can be used as welfare indicators. Understanding and responding to these behaviors improves welfare.
Net-pen salmon and trout communicate their welfare status through behavior, but only if observers know what to look for and care about what they see. Surface crowding, loss of coordinated schooling, excessive aggression, and abnormal swimming patterns all indicate welfare compromise in fish populations. These behavioral signals are the equivalent of the pain indicators used in terrestrial species - they reflect the fish's experience of its environment. Systems that monitor and respond to behavioral welfare indicators in real time represent a meaningful advance in aquaculture welfare management.