Pond Boss Forums Thread Like Summary - Fish kill

Help! Emergency, help! On yesterday I suffered a Fishkill of approximately 200 bream and one large mouth bass. At first I was clueless as to what it might be. Now I’m thinking that it may have been oxygen depletion. When I got home I saw the biggest fish, being one largemouth bass with its eyes popping out of its head. When I saw this, the first thing I thought was that it was likely a lack of oxygen. The pond is approximately 1/3 acre, it’s about 12 feet deep at its deepest, and there is no aeration on the pond. In the 11 years of the pond’s existence, I have never suffered a Fishkill before. One of the things I am doing now that’s different from before is, I am feeding the fish four times a day. I am guessing that with the heat, the increased feeding and the rapid growth of the fish with their waste in the water, And recently cutting the grass and allowing the clippings to fall into the water may have caused my issue. I believe that it is a combination of all of these things that caused my fish to suffer of a lack of oxygen. Can you please give me your thoughts.

By the way, the pond is stocked with bream and largemouth bass. There may be a few catfish in the pond. But, for the most part, the only thing I loss was bream. Also, I had been running well water into the pond for an entire week before the fish kill.

Experts will be here soon to help, I'm sure. In the meantime, sure sounds like you may be right. Hot water contains less DO, and all these factors put together might be the problem. If you've had some cloudy, calm days lately this isn't helpful, either. Well water is usually low in oxygen, by the way. Could be better to turn it off, or at least add oxygen to it.

If you have some kind of marine motor maybe you could run it to help oxygenate & aerate. And in your shoes I'd cut back on feeding, at least for now.

Feeding the fish will definitely increase the standing crop of fish. So in that respect yes it could add to the problems as far as a fish kill.

And any added biomass like grass clippings will take some oxygen out of the water as it decomposes. So that could be an additive problem. I try to throw the clippings away from the water. Once nutrients go into a pond there are few ways for them to get back out. Ponds tend to get higher in nutrients rather than lower. Any additions like feed or grass clippings add to that. A high nutrient pond does not have to be a bad thing, but it certainly takes more management to make sure those nutrients go into something that ultimately does what you want it to, namely raise fish.

Then it comes to harvest. One way to get the nutrients back out of the pond is harvest fish. A pond will only support so many pounds of fish. It might support more or less certain times of year, but if you have excess at the wrong time of year (usually hot still weather or when a pond turns over) you get a fish kill. One way to reduce that standing crop is to harvest fish. We fillet, eat and give away a lot of fish. But many do not want to clean and eat them. Another way to reduce the biomass of fish is fish a lot and rather than returning everything to the water, take less desirable fish or fish in a size class that are over abundant and process them back into fish food. Catching lots of small fish? Cut their tail fins and dorsal fins off and toss them back for an easy bass snack. You may find you even develop pet bass waiting for you to toss them a treat. I had some one year would hear my footsteps on the dock waiting for me to throw them fish. If it is a bigger size class of fish cut it in two or three pieces and toss it out. Big scissors work great for that. I have found my LMB will even pick the pieces off the bottom. How do I know? We were fishing with cut bait for CC on the bottom with fairly large fish heads on the hook and wife and I both caught LMB at the same time. We had been cleaning fish and throwing the contents back in to feed our CC and I guess the LMB got used to eating the cut up fish. If it comes to it, even using excess fish for garden fertilizer or wildlife feed is better than having a fish kill.

So harvest is an important part of pond management. And it becomes even more important if you are feeding because you are increasing the fish carrying capacity of the pond food wise without increasing it oxygen wise. Aeration would add the extra oxygen. So if you are going to feed, either add aeration OR take some fish out to keep from overloading the O2 levels.

If you add air, do the proper startup procedure or you could REALLY have a BIGGER fish kill. Nasty water lurks below the thermocline.