Do you have more than one of any of those? Some experiments would take a second fish to be the "control" if you want to get it past your science teacher. Here's some that only take one fish.
Stressless:
Feeding response times with diffrent foods.
Feeding response times in light vs. darkness.
Stress to fish involved:
Feeding response times at diffrent temperatures (or pick a diffrent water parameter that's easy to fix later.)
Do you have access to any fancy equiptment or rich relatives? Some of us would like to know if mollies raised in saltwater on saltwater foods have nutitional values similar to marine fish. Then when your experiment is over you can feed the leftovers to your aggressives.