To deal with predation threats, many prey organisms have evolved anti‐predator defences in both morphology and behaviour. Aquatic rotifers were among the first model organisms for studying inducible defences and studies mainly focused on predator‐induced morphological defences. Despite this, we still lack a good understanding of predator‐induced behavioural defences in rotifers. In this study, we conducted three laboratory induction experiments to investigate floating behavioural responses of the prey rotifer Brachionus calyciflorus to the presence of the predator Asplanchna sieboldii and its chemical cues. Two experiments used live A. sieboldii and one used A. sieboldii‐conditioned medium. Subsequently, we examined the protective effects of floating behaviour against predation by Asplanchna by performing predation experiment. We show that B. calyciflorus has a pronounced behavioural response to A. sieboldii and that this response can be induced by both exposure to live A. sieboldii and to Asplanchna‐conditioned medium. We also found that. B. calyciflorus can respond with floating behaviour immediately within 10 min when exposed to Asplanchna‐conditioned medium. We also provide the first experimental evidence that the floating behaviour of B. calyciflorus reduces the predation rate from A. sieboldii by about 50%, and effectively protects them from consumption by this predator. Thus, we concluded that B. calyciflorus can sense chemical cues released during predation by A. sieboldii and use behaviour as a defence, escaping to the water surface as a refuge, thereby reducing predation risk. Our results represent a novel addition to our fundamental knowledge on how prey may not be passive victims, but rather actively use inducible behavioural defences to counteract their vulnerability to predators.

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