Last week one of my koi, an 8 in beauty, disappeared...raccoon, cat, I don't know. (Netted pond to keep out predators, although I don't like the look. Haven't had a problem with predators before.) Yesterday, a thin 5 in comet emerged from a crevice on the side of my small (500 gal) pond. He seemed to have a difficult time swimming, spent a lot of time under the waterfall. He returned to his crevice a few times. He didn't eat. I decided to leave him. The other fish initially were curious, but generally left him alone. This morning he was swimming with the rest and joined them in feeding. The lower half of his tail fin is missing, but he seems much improved. I wonder where this guy came from. And! I wonder if the koi will similarly reappear, although I think he was too big to fit between the rocks. Comments?