Pharyngeal cavity and the gills are the target organ for the repellent action of pardaxin in shark.

Pardaxin, an active principle of the repellent secretion of the Red Sea flatfish, Pardachirus marmoratus, elicited severe struggling, mouth paralysis, and transient increase in urea leakage from the gills only when administered to the medium bathing the shark's pharyngeal cavity and gills. An apparatus was constructed which prevents a mixing of the outflow from shark's gills with water bathing its surface skin. It is concluded that in sharks the gills and/or the pharyngeal cavity are the target organ for the repellent action of pardaxin.