Endocrine, osmoregulatory and immune responses have been examined in blood plasma, gill, peripheral blood leucocyte (PBL), skin and intestine of steelhead trout Oncorhynchus mykiss reared for 4 weeks in seawater. Plasma lysozyme activity and pituitary growth hormone messenger ribonuculeic acid (mRNA) levels were higher and prolactin levels were lower in seawater than in freshwater. mRNA levels of hormone receptor and immune‐re...

To clarify the differences between migratory and non‐migratory salmonids during the parr‐smolt transformation, we conducted experiments on steelhead (SH) and rainbow trout (RT) Oncorhynchus mykiss . We examined relationships among different parameters of osmoregulatory, endocrine, immune, and stress‐related regulation in these fish following free selection of salinities. For this, we used an experimental halocline aquarium in...