The ice came off the pond a week or so ago. Found several fish floating on
the surface and several on the bottom. Pond is about a 1000 ga, 4ft deep at
the deep end. Pond has been in place for 4 years now with no problems. I
leave the pump running 24/7/365, turn the fountain off and leave the
waterfall run to keep things open.
Did the water quality tests once I found the dead fish. Everything was OK.
I did a major cleanout of the pond last Aug by netting all the fish (about
40 from 5" down to 1/2", removing the plants, draining the water and sucking
up all the black ooze that was on the bottom. Replaced all the water, (we
are on a well), did water samples, replaced the fish, fed the fish until
water temps dropped below 55 and waited for winter. Is it possible that with
the cleaning there were not as much food for them to forage on over the
winter? I have had more fish die in the past couple of days. The three
original fish from the beginning are still there and getting active. I
netted a couple of the smaller ones that were born in the pond and do not
see any issues with the gills or scales. I did a basic autopsy on one of the
dead fish and the stomach was totally empty.

I am stumped with this one. Did they starve or is there something else going
on.