Water fleas, or Daphnia, ensure their survival by reacting to a signal substance of their predators (fish) with flight. The zoologist Meike Anika Hahn from Professor Dr. Eric von Elert’s research group at the University of Cologne’s Institute of Zoology has identified this chemical messenger substance, which the fish releases into the water of lakes. When the water flea detects the substance 5α-cyprinol sulfate—a bile salt from the fish—it leaves the upper water layers and descends vertically into darker regions. The fish are unable to visually detect their prey there during daytime. This connection between the signal of the predator and the behaviour of its prey has now been published in the scientific journal eLife under the title ‘5α-cyprinol sulfate, a bile salt from fish, induces diel vertical migration in Daphnia.”