It took 70 years, but scientists have finally discovered how an injured fish notifies his peers when he is hurt, giving them the signal to bolt. It turns out that the mystery substance is chondroitin sulfate, a compound basically made up of sugar.
The fish release the substance after they're injured, and when others smell it, they immediately swim away. Scientists tested their theory by releasing chondroitin sulfate into tanks of zebra fish and watching them go crazy. Interestingly though, different fish respond to different versions of the chemical, so it's unlikely that dropping some chondroitin sulfate directly across from a net will help fishermen scoop up any record catches.
For more on the finding, don't miss this fascinating article over on io9.
[Image courtesy of Tom Weilenmann's Flickr stream.]