Alarm substance, or Schrekcstoff, is an mixture of compounds produced by specialized club cells in the epidermis of Ostariophysan fish. When lesioned, these cells release the substance, which acts as an aversive olfactory stimulus capable of evoking intense behavioral responses (alarm reaction) in other fish in the shoal (Maximino et al. 2018). Alarm substance is used as an aversive stimulus to study fear-like behavior in Ostariophysan - especially in zebrafish. The present protocol describes a technique to easily extract alarm substance for acute exposure.