I have come to find two 3 inch koi and two fan tailed comets gone in the past week. The other residents include about 6 2 inch feeders and 1 2 inch feeder minnow and a bullfrog the size of a 20 ounce gatorade lid. the pond is 18 inches deep all the fish hang out in the deep end. the only birds around here i've seen are doves and greckels those black raven looking birds that make tons of noise. I don't know if cats would go that deep and catch the fish but any help would be appreciated.