Ellen wanted to see if fish could “learn” by association.  She set up three identical ten-gallon aquariums.  The walls and tops were covered with black construction paper to prevent light from entering.  Ten feeder guppies were added to each aquarium as test subjects.  A small corner of each aquarium was left open, and a small reading light is placed over it.  Each day, the light is turned on over the aquarium, and thirty seconds later, a small amount of food is added to two of the aquariums.  The third aquarium is a control, and no food is added at this time.  Every five days for twenty days, the number of fish that come to the light before the food is offered is recorded.