Christmas day woke up to find out my pure white Ogan platinum koi had its mouth stuck open. You could see the muscles to the mouth contracting. I thought, "What is this"? Never encountered anything like this. I went to the koi vet site and looked through his articles. Sure enough I found one where a woman describes the same thing only her fish was not eating. In the end she had not found out soon enough what was the problem, and she lost her fish. Here is what was the problem a piece of gravel, sand , or rock lodges in the gills or mouth of the fish. Remendy take fish out,examine, and remove object. You have to look down the gullet, in the mouth, and in the gills. After her fish died, she found a stone lodged in the gills. Got up this morning to preform this duty on my fish and to my relief she was back to normal. It must have worked its way out.