A compound called schreckstoff (“Scary Stuff”)

“…a compound called schreckstoff. Many fish species excrete schreckstoff when they are injured. This alerts the rest of the school that danger is near. In a sense, fishes can actually smell fear. Schreckstoff was first documented in 1938 by Austrian ethologist Dr. Karl von Frisch [pictured here]. Because he didn’t know the chemical makeup of the compound, he simply called it schreckstoff—German for ‘scary stuff’.”

—So wrote Brandon Peoples, in The Fisheries blog.