Fig. 1

Experimental set up. A The test sequence comprises group and single emergence tests and subsequent open field test and mirror image stimulation for adults of the F0 (parental) generation (“Group emergence test” and “Single emergence test” in “Methods”). After subsequent reproduction per emergence rank (“Method of reproduction” section), F1 were subjected to a light dark challenge as larvae and to an open field test and mirror image stimulation as adults (“Open field test combined with a mirror image stimulation” section). After another round of reproduction per emergence rank, F2 larvae were subjected to a light dark challenge (“Larval behavioural testing: light dark challenge assay” section). B The emergence test assesses the individual tendency of risk taking, by measuring the rank of individuals from a group of fish (group emergence test) or the time of an individual fish (single emergence test) to emerge from a darkened holding compartment into an uncovered and potentially dangerous novel area, compartment. C The open field test combined with a mirror image stimulation was designed to establish a behavioural syndrome of correlated traits. The fish enters from a holding compartment into an open field. After crossing this potentially dangerous novel environment it encounters a mirror image stimulation. The parameters measured were related to locomotion behaviour and aggressiveness. D During the light dark challenge (LDC) test, larval fish are subjected to a series of alternating dark and light periods, during which they exhibit hyperactivity and hypoactivity, respectively. This behaviour is thought to be an anxiety like response to suddenly changing light conditions