Theo, I walk around the pond everyday. I also like to watch the fish feed on pellets. No cats. In looking back, I had 15-25 gills die within a month of stocking. I called Fenders and they said that was to many to die. They said something about having a problem on their end and offered to give me more. Which I did not take. This could have been low O2.This is about the time I saw 2 dead cats. My pond filled very fast and was muddy. Fenders said that did not matter and I should go ahead and stock. The winter of 03-04 froze over fairly long. New pond, no vegatation, muddy, ice, I bet you have hit on something. Winter kill. I would not see them die. Now that makes me wonder about the rest of the population. I see and catch bass. Seems like plenty of gills. Would you just add a few cats and observe things for awhile? No chem. problem back then, but I just did a dumb thing and used Princep to kill algae. Pond Boss told me that I made a big mistake. I am going to do nothing from now on without Pond Boss advise. Thanks, Tom