Light regime in aquaculture affects fish behaviour, physiology, and welfare; manipulated photoperiods are used extensively but their welfare implications require careful consideration.
Light manipulation in aquaculture serves production purposes — preventing maturation, improving growth rates, managing behaviour — but imposes welfare costs through disruption of circadian biology. Continuous light exposure disrupts sleep-like states that fish require for physiological restoration. The welfare cost of photoperiod manipulation has been underinvestigated relative to its widespread commercial application. Evidence-based lighting guidelines that balance production needs with welfare requirements for circadian rhythm expression are needed for major aquaculture species.