Note: Ogden Lindsley was one of B.F. Skinners' first graduate students, a past president of the Association for Behavior analysis, and one of the first behavior analysts to grasp the power of shaping with a conditioned reinforcer. As a professor at the University of Kansas, he required his own students to shape behavior; many of them used goldfish. The instructions here for clicker training a goldfish are easy to follow and make a good science project. Karen Pryor
We don't often worry about the mental state of a fish, but fishes enjoy stimulation and something to do, just as much as land animals. Aquarists know that the environment is important for keeping fish in good health or bringing them into breeding condition. That doesn't just mean places to hide and clean water to swim in; it can also mean a variety of foods including live food to chase, the right tank mates, the right plants, and, yes, an opportunity to learn.