Comparing the non-lethal and lethal effects of predation risk on goldfish anti-predatory behavior

Little egrets (Egretta garzetta) and common goldfish (Carassius auratus) interacted in experimental theaters that challenge them with a behavioral game. We studied the behavioral tactics of both players. The experimental theaters consist of three equally spaced pools, each with a shelter in its center. The fish can take shelter in a safe but foodless habitat, or swim exposed in the open that contains food. The egrets can move among the pools to catch the exposed fish. We investigated the importance of non-lethal effects versus lethal effects on predator–prey interactions. We created a variance in predation pressure by keeping the number of egrets fixed but varying the number of pools of the experimental theater between 1 and 3 pools. In all treatments, even when the egret was present, individual goldfish emerged from protected cover occasionally, exposing at least their heads and sometimes their entire bodies in apparent disregard for the possibly lethal consequences. We assumed that this behavior stems f...