Fig 3. Square experimental arena for the reference memory task.

(A): External view of the square apparatus used for reference memory tasks (Experiment 3 and 4): A plastic square tank, with four small corridors embedded in the four corners, was inserted in a larger tank and a surrounding comfortable area for fish (with gravel, plants, conspecifics and food) became an incentive to leave the apparatus. (B): Photographic enlargement of the square apparatus used for the reference memory procedure with panels (Experiment 3) and blue wall (Experiment 4): It is clearly visible the position of corridors into the corners. The presence of the glass jars kept the visual layout the same as Experiment 2.