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Alarm substances and fright reactions were found in three species of Cyprinidae from the southeastern United States (Notropis venustus, N. texanus and Hybopsis aestivalis). Three types of fright reactions were observed corresponding to the vertical distribution of the test species in the natural habitat (top‐water, mid‐water and bottom). Evidence was found that Gambusia affinis and Fundulus olivaceus (Poeciliidae and Cyprinodontidae) respond to skin extract from their own species with a reaction that may be comparable to the fright reaction known in the Ostariophysi and Gonorynchiformes. A predator odor capable of eliciting a fright response in local prey species was found in three North American predatory fishes \[Lepomis macrochirus, and Micropterus punctulatus (Centrarchidae); Esox niger (Esocidae)\] and in two South American fishes, Astronotus ocellatus and Cichlasoma severum (Cichlidae). The reactions to predator odor by the prey were similar in appearance to those observed in experiments using skin extracts from the prey species themselves. No damage to predator skin was necessary to release the substance which caused the alarm response. The origin of the predator odor was not determined; however, the water in which the predator had been kept was effective as an alarm substance.

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