|Abstract or Summary
- Detection of L-serine and D,L-alanine by juvenile coho salmon (Oncorhynchus kisutch) was measured in a two-choice Y-trough. Threshold concentration for olfactory
detection of L-serine was 10-8 M for zero-age parr, 1O-7 M for yearling parr, 10-5 M for smolts in late April-early May, and 10-6 M for smolts in June. Threshold for the
detection of D,L-alanine was 10-7 M for yearling parr, 10-6 M for smolts in late April-early May, and 10-5 M for smolts in June. Zero-age fish adapted to either freshwater or seawater were able to detect L-serine at 10-9 M. In vitro olfactory receptor assays and behavioral experiments were used to examine the specificity of L-serine detection by coho salmon. Of the 10 amino acids tested, L-serine, L-alanine and L-threonine were similar in their ability to compete for the serine receptor site.
All three of these amino acids as well as L-histidine elicited behavioral avoidance responses in a 2-choice Y-trough. Behavioral cross-adaptation experiments indicated
that the detection of L-serine was inhibited by the adapting amino acids L-serine, L-alanine, and glycine but not by L-threonine, L-aspartic acid, or L-histidine.
Classical conditioning experiments showed that serine and alanine were not discriminated from each other although either could be discriminated from L-histidine. These results, taken together, indicate that coho salmon perceive L-serine and L-alanine as identical odors. The olfactory detection of L-serine in a 2-choice Y-trough was inhibited by 2 hr exposures to mercury (Hg) or copper (Cu) but not by zinc (Zn). Upstream swimming behavior, however, was depressed by the presence of Zn as
well as Hg or Cu. Of these metals, only Hg strongly inhibited the binding of L-serine to its olfactory receptor. The inability to detect L-serine in the presence of Cu did not result from Cu masking the presence of serine. Chemical speciation calculations suggest that serine-metal complexation was not extensive enough to compromise olfactory detection. Thus, the mechanism of action of Cu is unclear whereas Hg appears to act at the level of the olfactory receptor. The ability to detect and avoid L-serine was not inhibited by a continuous exposure to Zn at 100 or 500 ug/L for 21 days.