Chemical transfer of warning information in non-injured fish

In this study we describe pacus, Piaractus mesopotamicus, detecting the pre sence of a predator by conspecific alerting pheromone. Moreover, we investi gate whether this chemical information indicates the presence of a specific predator, or whether it indicates general disturbance. We exposed groups o f pacus to the view of a predator fish (trahira, Hoplias malabaricus), a no n-predator fish (piracanjuba, Brycon orbignyanus) or an aquarium without an y fish (control), and then we transferred their water to isolated conspecif ics. We set up six trials of each condition in which we analysed the disper sion and the distance from the visual stimulus in water-donor fish and the distance from the chemical stimulus in water-receiver pacus. This study sho wed that pacus visually identified the presence of another fish and recogni sed it as predator or non-predator. This is interpreted as an innate respon se. Such heterospecific detection affects the behaviour of pacus, which rel ease chemicals that induce conspecifics to adopt a similar behavioural resp onse. At least two chemicals might be involved, one of them possibly an ale rting pheromone.