Many animals employ sex pheromones to find mating partners during their reproductive seasons. However, most sex pheromones of vertebrates remain to be identified. Over the past 20 years, steroids and prostaglandins have been identified as sex pheromones in several fishes. These pheromones are broadly termed “hormonal pheromones” because they or their precursors act as hormones in these fishes. Hitherto, no other type of sex pheromone has been unambiguously identified in teleost fish. Here we report the identification of a “nonhormonal pheromone” in teleost fish. The urine of the reproductively mature female masu salmon ( Oncorhynchus masou ) contains a male-attracting pheromone. Bioassay-guided fractionation yielded an active compound that was identical to l -kynurenine in spectral and chromatographic properties. l -Kynurenine is a major metabolite of l -tryptophan in vertebrates. This pheromone elicits a male-specific behavior at even picomolar concentrations; its electrophysiological threshold is 10 −14 M. l -Kynurenine is a reasonable substance for female masu salmon to advertise their readiness for mating.

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Aquatic organisms detect chemical cues to sense the local environment, for example, to find a mate, locate food, and identify danger. Knowledge of chemical cues can be used in aquaculture, in practical applications such as controlling mating behavior to increase fertility, enhance feeding, and decrease stress; in fisheries, by catching selected species with low-cost artificial attractants; and to address maritime issues, by decreasing biofouling. Aquatic organisms also detect chemical cues related to global environmental changes, ocean acidification, and increases in ocean plastics, all of which can affect their chemosensory behaviors. Here we discuss the nature of chemical cues and chemosensory biology and ecology of aquatic organisms, and potential applications with an emphasis on sex pheromones in commercially important and well-studied animals, namely, decapod crustaceans and fish.

Methyltestosterone-treated immature male masu salmon Oncorhynchus masou parr were attracted to both the urine of ovulated females and the ether soluble basic substances extracted from the urine, but not to immature female urine. It is suggested that the male response to the sex attractant (releaser pheromone) in the urine is under the control of androgens. 2000 The Fisheries Society of the British Isles

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