Ostariophysan fishes, which include fathead minnows, possess an alarm substance, or Schreckstoff, in distinctive epidermal club cells. The alarm substance is released upon mechanical damage to these club cells due to a predator attack, and can be detected by other ostariophysan fishes which then engage in antipredator behaviors such as hiding or dashing away. Fathead minnows learn to recognize an animal as a potential predator when it is presented in conjunction with the alarm substance. Also, alarm substance ingested by the predator will chemically label it as dangerous to naïve fathead minnows, thereby resulting in learned predator recognition. Prey fishes with chemical predator recognition abilities can inhabit areas with low visibility and more quickly detect ambush predators like the fathead minnow’s primary predator, the northern pike.