Recently, we identified the salmon olfactory imprinting-related gene in the olfactory system of one-year-old lacustrine sockeye salmon by using the subtractive hybridization technique of representational difference analysis.The predicted open reading frame of SOIG encodes a protein of 252 amino acids and shares low amino acid sequence identity with the urokinase-type plasminogen activator receptor. u-PAR belongs to a member of the Ly-6 superfamily that is found in several species. A Ly-6-related protein has been isolated from Caenorhabditis elegans, and it has been suggested that odr-2 may regulate olfactory neuron signaling within the neuronal network required for chemotaxis. Although the precise function of SOIG has not been clarified as yet, SOIG may have important roles in olfactory imprinting in lacustrine sockeye salmon. Thus, it would be interesting to examine changes in the expression levels of SOIG mRNA around PST by a real-time polymerase chain reaction technique. Juvenile lacustrine sockeye salmon in Lake Toya and Lake Shikotsu, Hokkaido, Japan, are spawned and released from hatcheries within a few months of emergence, and adults attain Rhein maturity in 3�C5 years and return to their natal hatcheries for breeding. The active spawning season is the middle of October to early November, but maturing adults gather near the shore of the hatcheries as early as September. The average (R)Ginsenoside-Rg2 homing percentage of lacustrine sockeye salmon in Lake Shikotsu was found to be 83% in both sexes, but these percentages varied depending on gonadal maturity. The smolting process in lacustrine sockeye salmon is not well understood; however we have found that the body color of one-year-old fish is silver and their fins are clear with intense black pigment in May, the condition factor is significantly lowin May and June, and serum thyroxine levels peak in May. From these data, we designated the period from April to June as PST in the present study. In the present study, electrophysiological and behavioral experiments were conducted to examine whether one-year-old lacustrine sockeye salmon could be imprinted by an amino acid, Lproline or L-glutamic acid before, during, and after PST.