When I was a kid in the western Rockies, our family had a very small ornamental fish
pond out back, with about 25 or so goldfish. We never fed them bought food; they ate what bugs found their way into the water, and occasionally we kids would catch grasshoppers and chuck them in. Those goldfish would tear them apart like little pirahnas--sometimes those grasshoppers were bigger than the fish!
We lived in that house for a few years, and the fish stayed in a tank in the basement over winter (the
pond was so small it would freeze solid)--we didn't feed them there either. Maybe we were bad fish owners? But we had a very low fatality rate (I think the only fatalities occurred in the tank not the pond, and were probably due to lack of oxygen), and after the first year, they began breeding, so we had even more fish.
This wasn't an aquaponics set up by any means, but if you have a couple of kids handy, I bet you could recruit them to collect a jar of grasshoppers/catepillars/other bugs once in a while to feed your fish. In fact, I have a little goldfish pond now, and I'm trying to convince my husband they don't need commercial fish food; the one we've got is soy-based and totally unnatural for a goldfish.