Pond Boss Forums FISH & FISHING Fly Fishing & Other Fish Species Dying Fish!

BACKGROUND: Ten years ago I acquired property in north Mississippi with a 5-6 acre pond with an average depth of around 4'. It has been consistently managed by commercial pond managers ... the former manager was bought-out last year, but the new company is a big outfit and seems high quality. There is virtually zero off-property watershed into the pond. Four years ago, the hay guy fertilized my pasture and the next year I had a B-G algae bloom, that was three years ago. There has been no other chemicals introduced in the ten years we've been here. It has always been stocked and restocked with catfish, largemouth bass and bluegill; most recently, in March it was stocked with 400 fingerling catfish and 100 bluegill. It has an automatic feeder which goes off once a day (in the morning), launching floating catfish food. It is fished, but not heavily. When fished, plenty of 1.5 - 3 lb catfish are caught and removed; a few bluegill are caught and removed; occasionally, but rarely, bass are the target, but generally no bass are removed.

The last week of June and early July were very hot, with heat index readings of 110 - 118 for several consecutive days. On July 1, I watched the fish feeder operate and it was a feeding frenzy, hundreds of catfish and a few bluegill were observed, churning the water. In fact, I told my wife that we need to have a big catfish fry to lower the population a bit. On July 3, I watched it again and there were no catfish and only a few bluegill ... I thought nothing of it and figured it was because of the heat. I left for a couple days, and on returning I found scores of dead catfish around the edge of the pond (and, thankfully, dozens of turkey vultures). Not knowing what else to do, I immediately turned on the well pump to hopefully cool the water and add oxygen; my wife called the pond management company.

Fish are continuing to die, but I'm not seeing as many floaters as before. The pond management company came out yesterday and drew samples for testing. He tested the oxygen level and said that it was very high, so that wasn't the problem. The complete test results will be available in 10 - 14 days. I don't know if it matters but the water is more clear than I've ever seen it ... certainly not crystal clear, but I can see the bottom in roughly 18" to 24" of water, which is pretty good for a farm pond in north Mississippi.

Notably, I've seen NO dead bass, only a FEW dead bluegill, and a plethora of dead catfish, mostly under 15". I know that not all of the dead fish float to the surface, but I feel that the relative numbers indicate that catfish have been hit hardest. I have turned off the fish feeder but dropped a couple handfuls of food off the dock, about a dozen bluegill appeared and NO catfish (previously, catfish would instantly appear for the pellets).

The pond is primarily used for training retrievers, but the side-benefit of having fish for my grandkids, neighbors and my wife and I to catch is certainly appreciated.

Does the Pond Boss Brain Trust have any ideas as to what could have caused the kill and solutions?

I appreciate any thoughts!!!

Thanks for reading!
GRR

Sorry about your fish kill!

Four feet deep (average) is pretty shallow for a pond of your size. That does not leave you much margin for error.

I think (non-expert) that is was actually low oxygen that probably caused your fish kill. The DO numbers your management company took are AFTER you turned on the well pump and started cooling and perhaps churning the water. (What is the source water for your well?)

Speculation (based on your very clear water and other results): Your pond was very close to the total carrying capacity of fish in that volume of water. Pellet fed channel cats can put on weight very quickly. (Do you re-stock, or are the CC breeding in your pond?) Also, the bass have to be getting much larger on their diet of pellet-fed BG, and they are also reproducing. Finally, you may have had an algal bloom going in your pond right when the hot weather hit. If your algal bloom started to die off, then they were starting to consume more oxygen through decay oxidation than they were producing, right at the time that the high water temperatures reduced the amount of dissolved oxygen that your water could hold. (Was it also nearly windless on your hottest days? Your high heat index numbers suggest it might have been. A 5-6 acre lake usually gets some of its oxygen through wave action.)

The combination of loss of oxygen producing organisms, plus pond near carrying capacity limit, plus very hot weather at a time close to maximum seasonal water temperatures, plus low wind, all conspired to cause your fish kill.

[There is a lot of speculation in what I have written above. Further, I would trust the judgement of good, local pond guys ahead of the advice from some yahoo (me) on the internet. However, they do have an incentive not to point the blame at any management lapses on their part in evaluating your existing fish populations.]

Hopefully some of our actual experts will drop into your thread. There are several members that have managed ponds after a large fish kill and can offer you some good advice.

Good luck on your pond rehab efforts! I suspect that a lot of your fish did make it through their recent crisis.

Thanks FishinRod!

I agree that 4' is too shallow, but the pond was already built when I moved here ... plus, it was lined with bentonite, so I don't really want to breach the bottom to make it deeper.

I also agree that the oxygen level was probably increased after I turned on the well, which was running constantly for 6 days before the management co. rep. got here ... plus, he drew water from near where the well water comes into the pond, so the sample was probably not representative of the other side of the pond. The well water comes up about 160' from, I guess, the aquafer.

Appreciate your comments!
GRR

Actually, your water source hurts my speculation. The water from a deep well should start with low oxygen levels. I don't know if the water from the well is agitated to atmosphere very much before it reaches your pond?

However, cooling the water does help increase the maximum oxygen saturation level of the water that is well-mixed with the atmosphere. Perhaps that, plus the 6 days of delay after the event, was enough to raise your measured dissolved oxygen levels?

I agree with you about the water depth. There is probably a very good reason that the pond is only 4' deep and lined with bentonite. I would not mess with breaking a good sealed pond bottom.

However, since you have a water well, then I assume you have AC electricity near the pond? If so, then you should probably read some of the aeration threads. An aeration system with several diffusers might save you from another big fish kill in the future.

Are you seeing any small bluegill in the shallows? I would set your fish feeder to the minimum time and see if you can get some fish to resume feeding. Usually a "low oxygen" fish kill takes out a higher proportion of the larger fish. I know that sucks, but hopefully you still have good base populations of BG, CC, and LMB to get your pond going strong again.

Dead fish in the pond no longer consume O2 except for decomposition, so there could be higher levels because of lower demand. O2 is lowest right before sunrise, if there is <6" visibility, the phytoplankton bloom could have caused the fish kill at night, then if the mgmnt. company came during the sunny day to check O2 it would be high.