The period immediately before harvest, when farmed fish are crowded for collection and transport to slaughter, is among the most acute welfare events in aquaculture. Managing crowding carefully is critical for fish welfare.
Pre-harvest crowding is the aquaculture equivalent of lairage for terrestrial livestock - a brief but intense welfare event that occurs just before slaughter. For fish, the welfare risks are acute: oxygen depletion in dense crowding situations can cause suffering from hypoxia, physical crowding causes mechanical stress and injury, and the rapid handling involved in pump and brailing operations adds further physical trauma. The duration of this phase matters enormously: fish that are crowded and immediately stunned and slaughtered have better welfare outcomes than those crowded for extended periods while awaiting processing capacity. Aquaculture welfare science is advancing in this area, with crowding protocols now included in leading certification standards.