Can zebrafish Danio rerio learn about predation risk? The effect of a previous experience on the cortisol response in subsequent encounters with a predator

Experienced zebrafish Danio rerio, when subjected to visual contact with a predator, did not show elevated cortisol levels and had values similar to control fish. The main hypothesis is that experienced D. rerio know about the real relevance of this prey–predator encounter. In summary, the data presented provide evidence that experienced D. rerio does not produce elevated cortisol in response to sighting a possible predator, and might suggest that these fish can learn about dangerous situations.