To determine whether the test fish were imprinted by a single amino acid, the electroolfactogram response to the test water was measured and the relative magnitude of the response was compared between exposed test fish and non-exposed control fish in June and October for three successive years. Behavioral experiments in a two-choice test tank were also carried out on maturing and matured test fish that had been exposed to Pro from March to July two years previously to determine whether mature fish could select Pro or not. In addition, the time required for imprinting by one amino acid, either Pro or Glu. Lastly, a molecular biological experiment was carried out to measure changes in SOIG mRNA 6H05 trifluoroacetate expression levels by real-time PCR. These physiological, behavioral and molecular experiments are discussed in relation to the odor properties of the natal stream, along with the imprinting timing and duration of lacustrine sockeye salmon. The results of our electrophysiological, behavioral and molecular biological experiments provide new information that increases our understanding of salmon imprinting by amino acids around PST. The EOG results reveal clearly that one-year-old lacustrine sockeye salmon can be imprinted by 1 mM Pro or Glu before and during PST. The behavioral results also show that maturing and matured fish that were exposed to the test water before and during PST 2 years previously have the ability to select the test water. Eighty percent of test fish imprinted before and during PST showed a preference for the test water, a proportion that is similar to the average homing percentage of lacustrine sockeye salmon in Lake Shikotsu. The electrophysiological and behavioral results revealed that there were significant differences between unimprinted control fish and experimental fish imprinted by a single amino acid before and during PST, and that the timeframe for imprinting timing ended after PST. The Oxysophocarpine composition of amino acids in the different streams feeding Lake Toya varies greatly, and the electrophysiological olfactory nerve response of masusalmon to artificial stream water reconstituted on the basis of amino acid composition has been shown to closely resemble the response to the actual stream water.