Binary patch assessment by goldfish under safe and dangerous conditions

•Theory suggest that animals make optimal foraging decisions with perfect knowledge of the patch quality.•We used “two patch system” (rich and poor resource density) to evaluate patch assessment by goldfish under safe and risky condition.•In the absence of a predator, the goldfish use an “assessment rule” and equalized the remaining resources between rich and poor patch.•In presence of a predator, they left higher resources in the richer patch suggesting a “fixed time strategy” when experiencing risk.•Prey animals may have adaptive foraging strategies to deal with safe or risky environments. Food resources can occur heterogeneously in space or time and differ in their abundances. A forager should be able to determine the value of a patch and choose optimally how to exploit it. However, patch choice and exploitation may be influenced by predation risk. Using the Giving up Densities (GUDs) technique, we evaluated goldfish patch assessment and choice in a binary patch choice experiment. We offered a pair of unequal food patches containing high and low food quantity. We quantified goldfish foraging behavior in the presence and absence of a predator. Goldfish groups equalized the GUDs in the two patches in safe environments but left higher GUDs in the rich patch under predation risk. The results suggest that goldfish can use both “patch assessment rule” and “fixed time rule” to exploit resource patches and trade off food and danger.