Scientists crack the 70-year-old mystery of why fish freak out

Schreckstoff literally translates as "scary stuff." It is both an example of German linguistic ingenuity and the mysterious chemical that has puzzled the scientific community for seventy years. It is the signal that wounded fish give off to scare the rest of the school away, but no one knew what this substance was...until now.

Wounded fish give off a signal that causes the fish around them to bolt. For seven decades, scientists have unsuccessfully tried to figure out what exactly tips off the other fish in a school. With the help of some very stressed out zebra fish, they finally found the answer — the chemical that makes a fish's fins flap is chondroitin sulfate.

This is technically a sugar. It's given off from the skin of a fish during an injury, which in turn causes the skin to give off an enzyme. Scientists don't think that this sugar was a defensive signal. Instead, they think that fish began giving it off coincidentally when they were hurt and the other nearby fish smelled the chemical, reacted negatively to it, fled, and survived to pass on their genes.

Chondroitin sulfate, like many other fish bits, has been shown to have some healthy qualities for humans. It's currently sold in health food stores as a treatment for osteoarthritis. Could you ruin someone's fishing trip with the right amount of chondroitin sulfate? Scientists had quite a time releasing the substance into alternate sides of an aquarium and making the zebra fish inside zip away from one side and then another. But they also discovered that different fish react to different "flavors" of the sugar. Alas, no guarantees with schreckstoff.

Image: Jon Hanson. Via Mayo Clinic and Current Biology.