I highly recommend training a male Betta in a bowl/small tank. They catch on pretty quickly, are not spooked by new items in their areas and are focused more on you then a fish housed with other fish will/would be. Male Bettas make great first fish for the first time fish trainer.
It is easier to train/work with a lone male Betta Fish then say a Guppy. Not that a person can not work with a Guppy, but guppies are normally kept in aquariums with many other Guppies. Male Bettas can and are kept in aquariums with other fish, but not other male Betta Fish. But if kept alone in a smaller bowl will be easy to train.
Betta Fish are simply beautiful. They are one of the few fish you can safely keep in a bowl. There are so many varieties and colors.
I have found with many species of animals, see our sister sites under the Navigation Menu, that training an animal to come Through A Hoop is an easy to teach, easy to learn trick. You can also move the hoop if the animal moves so that you can set the animal up for success, and that is very important when you begin training an animal. The first thing an animal needs to learn is to learn to learn.