LAUSR

Abstract Smoltification under intensive aquaculture conditions involves important physiological changes to intestinal structures that facilitate acclimation to hyperosmotic environments. This study evaluated if genic expression of primary contributors during the smoltification process in the intestine are in synchrony with gill Na+/K+-ATPase activity. Discordance was found between gill Na+/K+-ATPase activity levels and intestinal genic expressions. In particular, the intestine showed increased mRNA expression for prolactin, a hormone that participates in hypoosmotic environments, and in mRNA expression of the growth hormone, which mediates the hydromineral balance in hyperosmotic environments. These findings indicate a lack of sufficient intestinal maturation in the fish at the moment when they were transferred to seawater environments in the normal aquaculture practices. This intestinal immaturity is a possible explanation for the high rates of desadapted individuals in the seawater phase in Chilean salmon aquaculture.