Kairomones (from the Greek kairos, opportune moment, by stealth) are chemical cues from one species that another uses (“spying”). Primarily the receiver of the signal benefits, as in finding prey by odor, or detecting and avoiding predators by chemical cues. Since the cues are available to another species, they are considered “public” signals, in contrast to “private” signals of restricted pheromone systems, intraspecific by definition. Synomones are chemicals that regulate interspecific relationships where both partners benefit.

Section 12.1–12.7 discuss kairomones and Section 12.8 synomones.

Predator–prey interactions

Prey odors used by predators

Fish

Not surprisingly, much research in sharks, skates and rays has focused on the responses of sharks to human body odors. Human blood attracts sharks, while sweat does not, and urine was even slightly repellent (Tester, 1963). Practitioners use whale meat and mixtures of fish meal and fish oils as shark attractants. In both carnivorous and herbivorous bony fish (Osteichthyes) smell deals with prey odors, social odors, and chemical stimuli in homing, and it is mediated by the first cranial nerve, the olfactory nerve. By contrast, taste serves in detection and selection of food and avoidance of toxic food, and it employs the facial, glossopharyngeal, vagal, and hypoglossal nerves.

Numerous experiments with prey extracts have elucidated the stimuli that guide fish in their feeding behavior. These studies showed:

• rinses of prey organisms attract predatory fish and release food searching behavior

• predators can distinguish rinses of different prey species

• fractions of prey rinses also release feeding responses

• mixtures of amino acids are also active

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