Free Amino Acids Mediate Association Preferences in Fish

Chemical information is used in a variety of contexts including habitat recognition, foraging and predator avoidance, and a plethora of studies have shown that an individual's distinct chemical profile can mediate interactions with conspecifics. Interestingly, recent work has revealed that dietalone is sufficient to change the chemical profile of individuals, and with it, the way other individuals perceive and interact with them. Free amino acids are known to be utilised across species in a range of contexts, including during predator-prey and host-parasite interactions, and have been widely postulated to underpin diet-mediated social interactions, especially in fish. However, so far no empirical evidence has been presented to support this suggestion. Using an established behavioural assay in three-spined sticklebacks (Gasterosteus aculeatus), we aimed to assess association preferences in groups of fish fed experimental diets which differed by a single free amino acid. Our results demonstrate that free amino acids alone are sufficient to mediate interindividual association preferences, raising the possibility that such a mechanism may be widespread among aquatic animals.