Fig. 4.

Experimental set-up. G. petersii were individually housed in 75 cm × 40 cm × 40 cm tanks, which also served as the experimental arenas. (A) Schematic side view. (B) Schematic top view. These tanks were divided into two compartments (40 cm × 40 cm and 35 cm × 40 cm) by a partition with two closable gates behind which were positioned two objects (indicated in red) 1 cm from the gate. Distance grids, which were placed directly behind the gates and which could be passed by pushing them aside, made sure that the fish kept the correct minimal distance to the objects. The larger compartment (experimental area) was again divided into two compartments, one gate leading to each compartment.