Fish hiding and won't eat (after heron visit)

[Vita]

We have a pond for about a year with koi and gold fish. The fish was quite used to us and was almost eating from the hand. A few weeks ago we spotted a heron in the garden a few times. When we checked the pond after 2d time the fish was all hiding in caves. Later the did came out for feeding and we confirmed that they are all there. However they got much more timid since then and now don't come out at all even when we try to feed them (the food just collects in the skimmer). We have not seen heron since then (and we spend a lot of time in the garden), but can't guarantee it never came again. A week ago I bought 2 more small koi hoping that they will swim out and get the rest of the fish to come out. Unfortunately they also disappeared in the cave. Are they stressed? What can I do to get them back to normal? Do I continue try to feed them?

 

[j.w]

The heron will always come back as he has seen your fish. Put a net over them. That's what I did and now have peace of mind knowing that the bird can't get them. Once the heron figures out he can't get in under that net he will stay away.
I put mine up high attached to metal stakes. I can easily lift the net and hook it up to the rope so I can get under there to do any maintenance. I have a short metal fence around the bottom so the net does not touch the ground. Have it clipped to the top of that fence cuz my cats or other critters will get tangled up trying to crawl through it if it hangs to the ground.
Had to untangle one cat when I first put it up cuz I had it all the way to the ground. She was not a happy kitty!