I accidentally killed fish in one of my ponds a couple of years ago. If I had to guess I'd say 75% of the fish died. I went to scoop dead fish out of the water and noticed a good size bass swimming so I realized immediately not to buy fingerlings. Since it was early spring and close to spawning time I caught several bream and a few bass from my other ponds and transferred them home. I periodically did this for 2 years and I figured this would be the year I might could catch fish. It turned out I was 1 year ahead because last year there were several fish caught and plenty more this year. I believe the 2 ponds I caught fish out of to restock are some of the cleanest ponds in my area so I wasn't concerned with parasites, disease, etc.