It is not just aquarium enthusiasts who are discovering that fish are intelligent and have good memories - scientists are wising up too. Here is a description of a study that I found fascinating. It turns out goldfish can learn to keep track of the time, and adjust their behavior accordingly.
Dr. Phil Gee at the University of Plymouth showed that fish can learn to distinguish between different shapes, colors and sounds and can tell time. In his research goldfish were placed in a bowl in which they were fed only when they pressed a lever. The fish rapidly learned that pressing the lever produced a food reward. Once the fish were trained to press the lever, researchers set up the lever to work for just one hour a day. The fish soon became wise to this, and learned to press the lever at the same time every day. The activity of the fish around the lever increased enormously just before the set hour when their food was dispensed. If no food came out, they stopped pressing the lever when the hour was up. This demonstrates that the goldfish not only had an awareness of time but also remembered their prior experience and knew that there was no point to keep pressing the lever.
For those more scientifically inclined, here is the citation and link to the full text of paper:
Philip Gee, David Stephenson, and Donald E. Wright. Temporal discrimination learning of operant feeding in goldfish (Carassius auratus) J Exp Anal Behav. 1994 July; 62(1): 1–13. doi: 10.1901/jeab.1994.62-1. Free full text
Here is a graph from the paper, showing when the goldfish pressing the lever during a 24 hour period.
Notice how the lever pressing ramps up to nearly 60 presses per 15 minutes just before the food becomes available, and the peak is during that narrow "dinner hour" window shown as the yellow band. At other times of the day, the goldfish doesn't bother pressing the lever often, or at all, presumably having learned that it is a waste of effort since no food gets delivered.How cool is that?! Hmmm... Maybe that clock behind Comet's tank could be useful for more than just the webcam after all!