Alarm reaction of the top smelt, Atherinops affinis (Ayres).

The "alarm" substance of the top smelt, Atherinops affinis (Ayres), has been isolated by extraction with methanol or ether from suffocated top smelt. These concentrated extracts, when introduced into an aquarium containing top smelt, induce a strong alarm reaction in the fish, characterized by rapid swimming, jumping, and often severe seizures. The fact that extracts from white surfperch, Phanerodon furcatus (Girard); surf smelt, Hypomesus pretiosus (Girard); northern anchovy, Engraulis mordox (Girard); or Pacific herring, Clupea pallasi (Valenciennes) caused only mild excitation in the top smelt indicates the species-specificity of the alarm reaction.