I have a small 6 x 9 pond. Last year I had 5 fish (4 comet and 1 Shubunkin). Last summer we had babies, so the number was up to probably 11 or 12. In the winter I shut off the stream and add a tank deicer to keep the water open.
The problem for the past couple of years is that the fish seem to make it through the harsh winter fine. But when spring cleanout comes, I'm always missing a few. When the melting starts and water starts to go brown from runoff, I can't keep count of them, so I never know when they are missing. This year I added a grid of PVC and fishing line to deter any predators, though I have never seen any predators or tracks of predators.
I have just found the shubunkin floating. Thus begins my overwinter loss of fish. I'm wondering if the runoff and decay is too much for them. Perhaps I should start filtering earlier. I usually start the pump mid march to get the water cleared, though I bypass the stream and underground hose so I don't break it (ahem, as I did one year).
So does anyone have any ideas of what is going on?
Late Winter/Early Spring Fish Kill
Usually, goldfish can handle almost anything but chemicals. I had 2 that I put temporarily in a wheelbarrow, and forgot about them for a year, only to come back and find them in 1 inch of water that was covered in 2 inches of decayed leaves. They were double the size and very happy. I was completely shocked!
Koi are more fragile, but the comets lived through 100 degree temps, very little water, and then frosts during the winter.
I would assume there had to be a bit more than just spring dirty water or odd temps. True, the shubunkins are not quite as hardy as the true comets (you always lose a little durability when they get bred for pretty colors) but they still are pretty hardy.
I doubt there are any chemicals as I'm organic in the back yard. There is also only one fish dead at this point so I don't suspect a chemical kill. I thought perhaps the water has been too rich with organic nutrients for some of the older fish. But again, they aren't so temperamental of a fish that they'd need perfect water.
On a separat note, looks like most of the babies are Shubunkin/Comet hybrids so maybe more hardy. Maybe no more deaths this year?