Nature, nurture or interaction? It is important to make clear the effects of the genotype‐environment interaction on the variation in behavioral traits. Behavioral activity is one of the antipredator traits: lower behavioral activity reduces the predation risk, and also decreases foraging success. Such a phenotypic trade-off predicts the evolution of the phenotypic plasticity depending on the predator environment. Theoretically, it is adaptive to change quickly the antipredator trait depending on the predator environment, if the benefit outweighs the cost. Here, we analyzed the antipredator reaction-norm of clone lineages of the funa Carassius auratuss spp., which are exposed to variable pseudo-predation risks by piscivores under experimental conditions. As a result, the activity of fish raised with predators was lower than that of the control fish and the activity was different among the linages. Even after a month in a predator-free environment, the activity of fish raised with predators was still lower than that of the control fish. These results imply that: (1) the behavioral trait once developed is irreversible or sustained for a long time, and that (2) the funa develops their personality depending on the predator environment, if we regard the set of such longstanding behavioral traits as personality.

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