The a part of the frame that was placed inside the aquarium consisted of two 1. 4 cm diameter clear plastic rods e that terminated near the center of the aquarium at the outer fringe of the plastic ring. The Plexiglas rods allowed transmission of infrared light from one side of the aquarium to the other with out being refracted by the water. The ring was placed in the aquarium such that its starting was parallel to the long sides. When the fish swam in the course of the ring, breaking the photobeam, a response was recorded. A 25.