The smell of fish makes you a better critical thinker
The researchers conducted two separate studies. In Study 1, human test subjects were asked the intentionally misleading question: "How many animals of each kind did Moses take on the ark?" (hint: it was Noah, not Moses, who built the ark). The test subjects exposed to fishy smells were nearly three times better able to spot the "semantic illusion" (41% vs 16%).
The explanation for Study 2 is a bit more long-winded and outside the scope of an aquarist publication. It tested people's confirmation bias (read this article to learn about this principle) and found that subjects exposed to fish smells were significantly better able to work past their confirmation bias to arrive at the correct, logical conclusion.
TL;DR: (the smell of your) Fish make you better reasoners.
The research is published in the Journal of Experimental Social Psychology.