[Chemical danger signal in the "predator-prey" system in fishes].

Studies have been made on peculiarities of defensive reaction in Phoxinus phoxinus to external metabolites produced by the pike Esox lucius and excreted into the basin. It was shown that the skin and mucose of the pike contain low molecular weight substances (m. w. about 1300) which being introduced into the basin serve as a chemical signal of danger to Phoxinus phoxinus.