Some physiologic distinctions between freshwater and diadromous forms of the Atlantic salmon, Salmo salar L.

Abstract

Parr of the diadromous and freshwater forms of the Atlantic salmon, Salmo salar L., were cultured through the smolt stage in photoperiod and temperature cycles that were delayed 3 months relative to those in nature. Such environmental manipulations caused a delay of approximately 3 months in smoltification of diadromous parr, as measured by changes in water and lipid content and salinity tolerance. These changes did not occur in parr of freshwater salmon exposed to the same modified photoperiod and temperature cycle. The implications of this are discussed.