This could be used on any fish, but for purposes of training, you really need one that has its own tank, with no distractions.
So you've worked with the pen light for a couple weeks. Your betta now associates the flash with food.
Next, you want to teach them to come. The first thing is to pick a very clear hand signal. Bettas have great eyesight, they will eventually be able to differentiate between separate but similar hand signals, but until they get used to looking for you and interpreting what you want, you need something basic and easy for them to see.
Preferably something with movement, to get their attention. Eventually, you won't need movement, as I said, they'll know to look at your hands, to look for signals, but we need to teach them the ABCs before pronouns and prepositions.
I wiggle my fingers against the side of tank. Be consistent, whatever you choose, stick with it.
This takes place over multiple feedings. I only feed two (3 max) pellets at a time, so the steps take place over multiple feedings and multiple days.
The wiggling gets the fish's attention. As soon as he looks, flash and reward.
The next time, do not flash until he moves in the direction of your fingers.
Timing is key. Flash too soon, and he won't think he needs to move. Flash too late, and he won't realize that moving toward you is what you want.
As soon as his body moves toward your fingers, flash and reward.
Next, you will wait for him to move just a little bit more before flashing. Each time, you will gradually make him get closer to you, until he must be right against your fingers to earn his reward.
Since bettas are hunters, they're drawn to movement. Add to that the fact that he's already familiar with you and comfortable with you, and I've noticed this part of the training goes quickly.
The trick is (and the issue I'm having with my female now) is getting them to the point where they look for your hand. My female Neph is very quick to obey the command as soon as she sees it. The problem is she's not looking for it, even after we've done it once. She keeps looking to the surface for more food.
Of course, patience is key, and after a few seconds, she'll look around and see my fingers, and she'll come. So it's more than just training them to mindlessly obey. It's training them to be aware of you, to be ready and willing to "listen" to the "language" you're using to communicate to them.
It's teaching them to look to you. So that when you approach the tank, they're ready and alert and excited.
This is important because it builds a bond between the two of you. And that bond will be of paramount importance in Part 4, where I will show you how to train them not to fear the fish net. But honestly, anything you train them to do will require them to want to do it. And to make them want to do it, they have to have that bond with you. They have to associate you with positive mental stimulation, physical activity, fun, and (of course) food.
So training them to come is the next step, and it shouldn't take more than a few days. But patience is everything, and if you feel that your fish is taking longer, don't be discouraged. This is not something they do naturally. They don't communicate with humans in the wild (and that's literally what you're teaching them to do. To use a sign language to communicate a task or desire, that they interpret and understand).
So you're asking them to almost rewire their brain. To do something that doesn't come naturally to them. They're intelligent creatures, they're more than capable of doing it, and they enjoy doing it, but sometimes it takes them awhile for it to really click.
Just be patient with them, keep things positive, and be consistent. They'll get it.
Here is a video of it in action.