They ran a few hundred college students through a trust-based economics game. Some did it with fish smells, some with other unpleasant odors, and some with no odor at all. And what they found was that only those exposed to a fishy scent became more suspicious and less trusting of the individuals they worked with. Here’s more of the authors’ explanation of what, exactly, is going on:
When something smells fishy, something suspicious is going on. The present studies suggest that this is not merely fancy language, but reflects the use of metaphoric knowledge that has behavioral, cognitive, and perceptual consequences. Incidental exposure to fishy smells elicits suspicion about others’ intentions and undermines cooperative behavior in trust-based economic activity, whether it requires trusting others to reciprocate resources or to share responsibilities.
Why is the suspicious odor fishy in English but something else in other languages? It could be the result of recent evolutionary history, which is capable of generating cultural differences in genome-wide biological processes, including smell perception...We note that suspicion arises in social interactions and that odors indicating suspicion are organic (e.g., fishy, rotten). Accordingly, our speculation is that suspicion may be particularly relevant to the trading of valuable products that are organic, decayable, and smelly when decayed, like fish and meat. Encoding such cultural knowledge in language might have given rise to local variants of the smell–suspicion metaphor.
Full paper here.