Identification of olfactory alarm substances in zebrafish.

Escaping from danger is one of the most fundamental survival behaviors for animals. Most freshwater fishes display olfactory alarm reactions in which an injured fish releases putative alarm substances from the skin to notify its shoaling company about the presence of danger. Here, we identified two small compounds in zebrafish skin extract, designated as ostariopterin and daniol sulfate. Ostariopterin is a pterin derivative commonly produced in many freshwater fishes belonging to the Ostariophysi superorder. Daniol sulfate is a novel sulfated bile alcohol specifically present in the Danio species, including zebrafish. Ostariopterin and daniol sulfate activate distinct glomeruli in the olfactory bulb. Zebrafish display robust alarm reactions, composed of darting, freezing, and bottom dwelling, only when they are concomitantly stimulated with ostariopterin and daniol sulfate. These results demonstrate that the fish alarm reaction is driven through a coincidence detection mechanism of the two compounds along the olfactory neural circuitry. [Display omitted] • Ostariopterin is a "danger signal" commonly present in many freshwater fishes • Daniol sulfate is a "conspecific signal" specifically present in Danio fish species • Ostariopterin and daniol sulfate activate distinct olfactory circuits in zebrafish • Coincidence detection of these two molecules triggers robust alarm reaction In 1938, Karl von Frisch postulated the existence of olfactory alarm substances (Schreckstoff) in fish. Masuda et al. identify two compounds in zebrafish skin extract, ostariopterin and daniol sulfate, which act as "danger" and "conspecific" signals, respectively. Only when they are concomitantly applied do zebrafish display a robust alarm reaction. [ABSTRACT FROM AUTHOR]