Pawsitive Experiences Training Details for Teaching a Fish to Swim through a Hoop
Comet the Goldfish Tricks-R2FishSchool.com training kit (Amazon)
Karen Pryor Training an Oscar Fish-shows paying attention to your learner (fish frustration when it did the trained behavior and she accidentally ignored it)
Dolphin Creativity-Do Something Different (which can also be taught to advanced dogs)
These videos show how positive reinforcement works in training other animals.
Success-based, positive reinforcement marker training can teach any animal to do whatever is withing their physical and mental ability.