Hehe, it's incomplete and quite simple, but the gist of it is: You have two AR marker cards for positioning a bunch of seaweed (the spawn point) and a hole ("home base") onscreen. Once you've got those set up, you tap a button to spawn a fish in the seaweed. By default, it'll swim straight to the hole, but every now and then, coins spawn around the area, and the fish will pick the nearby ones up before swimming back home.

There's a big predator fish roaming the area and the instant a fish appears, it makes a beeline for it, and eat it if it doesn't get home in time. The longer it spends away (picking up coins), the more likely it is to be eaten. So the whole game is a balancing act between positioning your seaweed and home such that your fish pick up the most coins while also avoiding getting eaten.

I'm really glad I got it working, I was kinda tearing my hair out over it for a while!