Any aquatic organism transitioning between life in freshwater to saltwater must address divergent osmoregulatory challenges in these environments to maintain or quickly reinstate homeostasis. Survival following the transition from freshwater to saltwater necessitates a reversal in the functioning of osmoregulatory organs/tissues, such as the gills, gut, and kidney. Among salmonids, these physiological changes are accompanied by morphological and behavioral changes that collectively define a transformation known as “smoltification”.
Different strategies can be used to manage parr-smolt transformation in production aquaculture, including photoperiod manipulation (i.e., ‘winter signal’ followed by continuous light) and the use of smoltification feed. SuperSmolt™ Feed Only (SSFO) is a smoltification feed containing a proprietary blend of sodium chloride, free tryptophan, and magnesium and calcium salts that induces smoltification via stimulation of calcium-sensing receptors in the fish’s body. SSFO induces smoltification in obligate anadromes, like Atlantic Salmon and Coho Salmon, without the need for photoperiod manipulation. Additionally, SSFO can induce smoltification in facultative anadromes, like Rainbow Trout/steelhead, that are largely unresponsive to changes in photoperiod.
SSFO has been used primarily to smoltify commercially reared juvenile salmon before seawater transfer, but it is now increasingly being used as a tool to prepare commercially reared trout for grow-out in sea cages and in public hatcheries raising various anadromous salmonids for conservation purposes. This presentation will briefly review the physiology of smoltification—what happens, when, and how—and provide insights from recent research involving managed smoltification using SSFO.