Diagram of the experimental setup for the open field paradigm. A white plastic 40 × 40 × 8 cm square arena was placed on a blacklight table illuminated with infrared LEDs. An infrared camera was placed above the arena to record fish behaviour during the trials.

Daily variations of individuals’ behaviour in the open field test (experiment 1). A. Time in edge of the arena; B. Distance travelled; C. Freezing behaviour (time spent motionless). Dotted orange lines indicate significant daily rhythms (p < 0.05) based on best-fitting models calculated by Cosinor analysis. Data points are mean ± SEM. Different letters indicate statistical differences by means of Tukey HSD test. White and black bars above each graph represent light and dark phases, respectively.

Daily variations of zebrafish shoals’ behaviour in the open field test (experiment 2). A. Time in edge of the arena; B. Distance travelled; C. Freezing behaviour (time spent motionless). Dotted orange lines indicate significant daily rhythms (p < 0.05) based on best-fitting models calculated by Cosinor analysis. Data points are mean ± SEM. Different letters indicate statistical differences by means of Tukey HSD tests. White and black bars above each graph represent light and dark phases, respectively.

Daily variations of shoals’ behaviour after familiarisation with the open field arena (experiment 3). A. Time in edge of the arena; B. Distance travelled; C. Freezing behaviour (time spent motionless). Dotted orange lines indicate significant daily rhythms (p < 0.05) based on best-fitting models calculated by Cosinor analysis. Data points are presented as mean ± SEM. Different letters indicate statistical differences by means of Tukey HSD tests. White and black bars above each graph represent light and dark phases, respectively.