ABSTRACT Objective Anadromous salmonids undergo a preadaptive transformation to prepare for life at sea known as smoltification. Smoltification has been investigated since the 1830s, first to understand it as a physiological phenomenon and then to control it for the purposes of intensive aquaculture. Photoperiod manipulation is a well-established means of smoltifying some species, but diet-induced smoltification is an increasingly common, if less well researched, practice that demands greater attention. Methods Published literature and aquaculture industry practices were reviewed. Results Increasing day length is a potent cue for inducing smoltification, and photoperiod manipulation has been used to synchronize smoltification in salmon farming for decades. Certain seasonal changes in water chemistry may also serve as smoltification signals, and salmonids can detect these changes via calcium-sensing receptors (CaSRs). When appropriately stimulated by calcium, magnesium, or other ligands in the environment or in the feed, CaSRs prompt smoltification. Photoperiod manipulation is still widely used, but methods based on CaSR stimulation are now also commonly employed. Conclusion This review summarizes the state of knowledge regarding light- and diet-stimulated smoltification and methods for assessing smoltification status. Gaps in understanding and application of these strategies are addressed, along with future directions for the science and practice of controlled smoltification.
Trushenski et al. (2026) studied this question.