Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Did I accidentally kill my fish?

Hi All,

Purchased a home with a fresh-water pond already full of some pretty big Goldfish & Koi, Blue Gill, Bigmouth Bass, Sunfish, Catfish. frogs and turtles. I'm not raising them or doing anything other than feeding to keep them alive and keeping the pond clean. However, I do allow neighbors to catch and release. Today when a neighbor went to fish he noticed an alarming amount of goldfish and large (nearly adult) tadpoles floating on top There were at least 20 dead goldfish/koi and what looked like hundreds of dead tadpoles at the edges of the pong. Some dead fish were even out of the water in the yard. Not sure if they jumped out the water or our neighborhood Heron dragged them out. We also noticed several goldfish and tadpoles still alive at the water's surface, but moving very slowly and struggling to survive.

Strangely, all of the other fish seem to be surviving fine and acting normally. I threw out some food to test the response and the other fish ravished it up as they always do. My neighbor cast his line to see if anything tried to bite and they did. Matter of fact, he caught a Blue Gill, which we looked over, tossed back in and it quickly swam away like normal.

The only thing I can conclude is that it's an oxygen issue, which I'm wondering may be due to a herbicide treatment that I did on last Sunday. This would be odd, since I used the same type and amount that I always have, nothing else had changed that I'm aware of. When I fed the fish on Monday they seemed fine and my neighbor said they seemed fine when he was fishing on Tuesday. Also, if it were a lack of oxygen, wouldn't it affect the other fish?

The only other difference since Sunday was that I turned the fountain off on Thursday during a bad thunderstorm, which was still off today. I work nights and was heading out to work when I discovered this, so I didn't have time to remove the dead fish or attempt any other remedy yet, besides turning the fountain back on.

Is it possible that I disrupted the oxygen circulation after the herbicide treatment when I turned off the fountain? If so, how do I fix it and save the fish? I feel terrible to think I may have caused this.

What herbicide did you use?

Typically it's the biggest fish that die for lack of O2, but tadpoles and also utilize atmospheric air so I doubt it was an O2 issue. But that's just a guess from Northern Indiana.

Your actions may be in conflict with each other.

Feeding adds nutrients to the pond, which promotes plant growth that you are applying herbicide to deter. If you aren't feeding to add size to the fish in your pond, or produce more pounds of fish to remove and eat, why feed?

Catch and release is a great practice for public BOWs where it is needed to preserve, say, bass populations in the face of high fishing pressure and bass tournaments. But a pond is (as Bob Lusk has written several times) like a garden, where you have to harvest what you grow lest is become overpopulated (especially if you feed).