Dietary manipulation keeps salmon in the smoltification window roughly twice as long as photoperiod-based methods, according to a review conducted by Norwegian scientists in collaboration with STIM AS and STIM Chile.
The review, published in the paper “Smoltification strategies in intensively cultured salmonids,” examines both approaches across Atlantic salmon (Salmo salar), coho (Oncorhynchus kisutch), and rainbow trout (Oncorhynchus mykiss) — the three species central to Chilean aquaculture.
Poor or asynchronous smoltification causes physiological stress, reduced feed intake, slower growth, size variability, and higher mortality. The review links suboptimal smoltification to weaker immune response and reduced vaccine efficacy — a direct concern in Chile and Norway, where infectious diseases remain the leading cause of mortality.
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Photoperiod-induced smolts that are not transferred to seawater quickly revert to a freshwater phenotype, losing smolt characteristics. Diet-induced smolts hold their smolt window longer and show stronger results in NKA enzyme expression in the gills — a key indicator of marine osmoregulation readiness.
For rainbow trout specifically, photoperiod and temperature manipulation has produced limited results in smoltification markers. Dietary induction showed positive outcomes in smoltification index, gill NKA gene expression, and sea water performance, the review states.
Dietary strategies depend on active feed consumption. Low water temperatures and social dominance hierarchies within tanks can reduce effectiveness.
The authors caution that conceptual errors and incomplete knowledge have led to suboptimal smolt quality and production losses across the industry. They call for continued research, particularly on species other than Atlantic salmon, where understanding of the smoltification process remains limited.