Photoperiod manipulation using artificial light is widely used in salmon hatcheries to control smoltification timing, and understanding the welfare implications of light management is important for optimizing protocols.
Light management welfare in salmon hatcheries occupies an area where production optimization and welfare science are beginning to converge. Photoperiod manipulation is commercially essential for controlling smoltification timing across production cycles, but the welfare implications of artificial light regimes for fish that evolved under natural light cycles are receiving increasing scrutiny. Constant light exposure, used in some hatchery systems, disrupts the circadian rhythms that govern normal physiological function in salmon. Welfare-conscious light management uses gradual transitions between photoperiod phases, maintains some period of darkness for rest behavior, and avoids light intensities and spectra that cause avoidance or behavioral disturbance. The integration of smolt quality metrics with behavioral welfare indicators provides a more complete picture of light management welfare impact.