low pressure button?

I'm building a fish feeder with my son. The fish will activate a food pellet to be dispensed by pressing a button. Can anyone suggest a button that a small fish could press to activate the feeder? One idea we've had is to use a single click button with an extension into the water, but we don't want the fish to have to press to hard. Ideally, we'd just like him to touch it. I'm not sure what type of touch sensor would work for a pet fish under water. We are working on a few ideas and are also making a "hoop swim through" with an IR obstacle detector.

Tricky one. The simple two-pieces-of-wire switch isn't going to work very well in water and most zero-force switches like capacative won't work in water either.

Can the switch mechanism can be out of the water? Like a thin rod dangling into the water and you detect when that moves? Make the top part metal wire and loop the other contact around it, with very little space. This will be tricky to set up and might be too easily disturbed.

Or do it with IR, like your hoop detector except the hoop is closed and the fish can't swim through. It just has to get close enough to touch and it breaks the beam.

I don't know if fish like touching things this way. They probably don't like having to reverse away from a solid object. But they must eat off the bottom sometimes, so they must have some way of doing it.

MorganS:
Make the top part metal wire and loop the other contact around it, with very little space. This will be tricky to set up and might be too easily disturbed.

This sounds like a great way to make a switch that's sensitive enough! Thanks! We're going to try it.