While researching an article, I found out that shrimp have the hormone serotonin circulating in their systems, the same hormone that improves mood in humans. When exposed to one of the chemicals in Prozac, shrimp will see their serotonin levels skyrocket, and they'll start behaving in abnormal ways, like swimming out of their safe, dark hidey holes toward bright areas where predators can find them.
Take what you will from that. The lesson I took is that happy creatures do stupid shit.
Read more about conked-out crustaceans here.