Biology
The Role of Chemical Cues in Predator Recognition and Avoidance in Prey Fish
Quick fact
Fathead minnows that have never encountered a predator can learn to recognize a novel predator's odor in just one trial by pairing it with the alarm cue released from a wounded conspecific, and this learned fear can last for at least three weeks.
Why this is interesting
Imagine a fish that has never seen a predator, yet it freezes and hides when it smells one. How does it know to be afraid?