(A) Cortisol profile in injected zebrafish. Embryos were microinjected with either vehicle (control) or 75 pg cortisol [Means ± SEM, n = 4–9 (pools of 20)]. A significant interaction was detected (two-way ANOVA/Tukey, P < 0.001). Significant time effects within treatment groups are indicated by different lowercase letters; significant treatment effects within time points are indicated by asterisks. (B) Total activity in light and dark period. Activity of 96 hpf larvae expressed as total distance travelled in 30 m. Cortisol levels corresponds to those at 96 hpf (see A). Means ± SEM (n = 72). Different letters indicate significant differences (Student’s t-test, unpaired). (C) Mean activity in light and dark. Activity (96 hpf) is expressed as total distance moved during each 30 s recording bin. The total recording period was 1 h with alternating light periods of 7.5 min each, indicated by the light and dark bars above the x-axis. Means ± SEM (n = 72). (D) Thigmotaxis. Arenas (wells) were divided into inner and outer zones, and the propensity to stay close to arena wall (96 hpf) is expressed as % of total distance travelled in 30 min that occurred in the outer zone. Means ± SEM (n = 48). Different letters indicate significant differences (Student’s t-test, unpaired). (E) Representative path for thigmotaxis. Inner and outer zones shown, in addition to a representative 30 s travel path for one larvae in each treatment group.