I have 3 ponds on my property and lost koi and perch and sunnies from each one, sadly it seems that the biggest fish were lost. I thought it was a total kill, but on my walk today I found a group of about 10 koi ( 2 big ones 8 sm.) swimming together near the top in the middle of one of the ponds. Having read this post it confirms what I thought...That it was from low oxygen. It was strange, during early ice I could catch all kinds of perch and sunfish through the ice, and as winter dragged on it got tougher to find them. Now with the ice gone I found floaters. The only one happy about the dead fish are the coons who have been munching away nightly