Ambicoloration in farmed halibut, where the normally white underside develops dark pigmentation, is a welfare indicator linked to chronic stress from inadequate substrate and light conditions.
Ambicoloration in halibut serves as a visible welfare indicator that reflects underlying physiological stress from conditions that prevent normal bottom-resting behavior. The high ambicoloration rates in some production systems indicate widespread welfare compromise that is both preventable and correlated with measurable physiological harm. The practical implication for welfare improvement is clear: providing appropriate substrate for resting behavior addresses the root cause of ambicoloration and the associated stress responses. Ambicoloration monitoring therefore provides halibut farmers with an accessible welfare metric that requires no specialist equipment, making it a useful component of routine welfare assessment programs.