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Use hoops, arches, plants, etc. to make your fish tank into an obstacle course. Once you've taught your fish how to swim through hoops, they should be able to swim through and around anything with some guidance. Be patient when teaching your fish how to swim through an obstacle course, as it may take some time. Your fish will most likely follow your finger around once it has mastered that trick, so lead your fish through its obstacle course. Start with simple obstacle courses, and make them harder once your fish starts to master the obstacles. Use a treat on a string or a hood to lead your fish around instead of your finger. If you want your fish to follow you all around the tank, it may be hard for you to use your finger. Stick a treat on a hook, stick, or string and move it around the course so that the fish follows it. Make sure the fish doesn't get the treat until it's finished the course. Just like all the other tricks, positive reinforcement will help train your fish quickly. Give them a treat every time they complete the obstacle course. If you've had the treat on a hook, make sure to remove it from the hook before feeding it to the fish.

Summary:
Decorate your fish tank like an obstacle course. Lead your fish around the course with your finger or a treat. Reward your fish with a treat after it completes the obstacle course.