I like to see what motivates people. Personally, I've always found that the carrot works much better than the stick. People simply appreciate rewards more than punishment. But also, if that's not working, you can just whack them with the carrot, instead.
Aquarium fish are pretty, but they make awful pets. For one thing, they're just not very cuddly, all slimy and gasping for breath the whole time. Also, they always leave a wet spot on the bed. But more importantly, they never live long and you just end up having to flush them down the toilet.
I think a puppy would be a better choice for a pet, since they're more cuddly. On the other hand, they're much more difficult to flush.