Predation is a strong selective force acting on both morphology and behaviour of prey animals. While morphological defences (e.g. crypsis, presence of armours or spines or specific body morphologies) and anti- predator behaviours (e.g. change in foraging or reproductive effort, or hiding and fleeing behaviours) have been widely studied separately, few studies have considered the interplay between the two. The question raised in our study is whether antipredator behaviours of a prey fish to predator odours could be influenced by the morphology of prey conspe- cifics in the diet of the predator. We used goldfish (Carassius auratus) as our test species; goldfish exposed to predation risk significantly increase their body depth to length ratio, which gives them a survival advantage against gape-limited predators. We exposed shallow-bodied and deep-bodied goldfish to the odour of pike (Esox lucius) fed either form of goldfish. Deep-bodied goldfish displayed lower intensity anti- predator responses than shallow-bodied ones, consistent with the hypo- thesis that individuals with morphological defences should exhibit less behavioural modification than those lacking such defences. Moreover, both shallow- and deep-bodied goldfish displayed their strongest anti- predator responses when exposed to the odour of pike fed conspecifics of their own morphology, indicating that goldfish are able to differenti- ate the morphology of conspecifics through predator diet cues. For a given individual, predator threat increases as the prey become more like the individual eaten, revealing a surprising level of sophistication of chemosensory assessment by prey fish.
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