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.