Unexplained Fish Kill in Pond

[Mary Cody]

Hi Folks, I have a 1/3 acre man made pond. It is 8' deep on one side and about4' deep on the other. All of a sudden I have fish dying. Big catfish, up to 10 lbs, bass 3-4 lbs, brim, all dying. Even my grass carp that is 40" long and weighed 35 lbs died. No dead frogs, no dead minnows, I can tell that there still are live fish in there. We have had no rain for the past 2 weeks, so nothing has flowed in the pond to poison it. In the past, even the bad drought that we had 2 years ago didnt affect it. No one has sprayed their fields in the area. I have had a lot of duck weed in it this year, could that do it? What could be killing my fish?

[fishhead]

If the duckweed covers enough of the pond surface it could be stopping the sunlight from reaching the plankton to produce oxygen. Do you see any fish swimming along the surface swallowing water? That would indicate low oxygen.

[snowshoehair]

A sudden spike in some sort of an algae bloom can take the oxygen out of the water, killing the fish. We had a large amount of silver salmon smolt in the southern part of the state killed that way... I think it was just this past spring.

http://homernews.com/stories/061809/fishing_3_003.shtml

[chickenista]

Chickens, ducks, turkeys etc... love duckweed and it is very high protein.
You could scoop it up and feed it to your critters as a way to clean it up.

[Mary Cody]

Thank you Fishead and Wind, I think that may be what happened. I was walking around the pond the day before the kill, and spotted a couple of Big catfish at the edge.. I thought they were sleeping, they were moving slowly, but could have been gasping for air. I even touched one, and it slowly swam to the deep. Next day they were belly up. I guess we lost about 2 dozen big fish. I will go get something to get rid of the duckweed but not hurt the fish....do they make anything like that? I have the blue algae killer stuff, but it doesnt take care of duckweed. Dont have algae, anyway. And I dont want to go buy ducks.

[cc-rider]

What is it that they call "pond turn over"? I don't have a pond, so didn't pay much attention, but it happens, all of a sudden, at this time of year. Something to do with the water temperature and such. I guess all of a sudden the water flips so the hot is on top or visa-versa, and it kills a lot of fish. And that you can control it with aerators, etc, so the water doesn't get the temperature strands. Dunno.....just something I kinda heard and didn't understand. Could that have anything to do with it?

[MJFarms]

I agree w/ CC-Rider. They call it an inversion. It is rare but I had it happen a # of yrs ago. Nothing you can do about it. Pond will correct itself and you can restock right away if you think it damaged the population. May happen again tomorrow or never in your lifetime. Mine has only done it once in 15yrs.

[poppy]

Yep, inversions are not uncommon this time of year. I haven't had it happen, but a friend of mine lost his fish twice in 4 years because of inversions. His pond is 14 feetdeep and mine is only 9.

[plowjockey]

An aerator will add oxygen and help move excess nutrients around, so they will dissolve faster. The excess nutrients is what cause the algae and weeds.

Currently saving up to get the pump and parts to build one myself. Love to have a wind powered model, but it's a little hard to justify the $1000+ cost for one.

I'd recommend an aerator for every pond that is not spring or creek fed.

[coup]

is there any shade on the pond and what were daytime temps.........maybe should have taken a water sample.........

[Alice In TX/MO]

We have also had ick in our ponds. It's a fish disease.

http://www.peteducation.com/article....+2160&aid=2421

[Riverdale]

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[Riverdale]

Sounds like oxygen depletion to me, especially if it is just the bigger fish (since frogs 'breathe' air, the would not be affected by depletion, but would be one of the first if there was a 'poisoning' of some sort).

to aerate, could you get a cheap shallow well pump (around here new for $150 or so) and rig it to curculate with black plastic pipe? That is all aquarium bubblers do. You would need to screen off the inlet to keep lil fish and tadpoles out, but hey

[Cabin Fever]

IN my recollection, thermal inversions happen only in spring and fall in deeper bodies of water than a farm pond. Could be all that algaecide you used killed the algae (which supplies dissolved oxygen to water) and now the dead vegetation is decomposing in the pond (which consumes dissolved oxygen).

[KMA1]

Mary Cody,

If you have a disolved oxygen problem, which is almost certain from your posts, the last thing you want to do is put something into the water to kill algae or the duckweed. If you kill the duckweed or algae now, their decay is extremely likely tol drop the disolved oxygen concentration to near 0 and kill all or most of your fish. The only thing you should do right now is aereate the water. You can do this eithr with a mecanical aerator or by pumpimp the water from the pond and getting a spray (best) effect, or by running the water over something flat and level so it spreads out and and drops into the watr causing splashing.

[KMA1]

Sorry about the typos in my last post. The last thing I wanted to add is that if you have an algae problem and/or a duckweed problem, it is likely you are getting nutrient rich runoff (to much fertilizer) on the drainage area around the pond. The best way to control it is by controling what you put on the drainage area if you own it.

[fishhead]

Did you treat the algae a few days before the fish kill? If so that would lead me to believe that decaying algae is what consumed the oxygen plus it would no longer produce oxygen.

You can use White Cap/Sonar/Avast. It kills slowly so doesn't cause low oxygen and it's safe for fish, tadpoles, and you. It will kill vegetation along the shore though so be aware of that impact. I think it kills duckweed but I'm not positive.

You shouldn't need an aerator if your pond gets sunlight over 1/2 of it.

Sometimes phytoplankton (single celled) algae populations just crash and that is followed by low DO. I just had a pond do that. Why did it do it? I have no idea because nothing was done to the pond. It's fine now but for a whole 24 hours the minnows were gasping at the surface. Larger fish can't do that and are the first to die.

[Mary Cody]

Thank you all for your input. We got a pump and began aerating the pond. I had not put anything in the pond 2 months prior to the kill. So I am convinced that it was lack of oxygen. Had no more fish die in 3 days, so we are looking into a more permanent type of contraption to keep the water moving. Filling up the pump gas tank every 4 hours gets old. A nice fountain of some sort will help, but getting power to run it could be tricky. We lost our last grass carp. it was 42 inches long and about 35 to 40 pounds.

[fishhead]

You shouldn't need anything but an emergency aerator to be turned on only if you see fish at the surface.

I use submersible pumps in some of my ponds at times during the winter. Oxygen demand is low and a small water garden pump can keep a 1/2 acre pond alive.

If power is too far away you can always push air to the pond through 3/4" black polypipe and a small rotary vane compressor. It will push air for hundreds of feet.

If duckweed is a problem then more grass carp are needed. Also, younger smaller grass carp are more effective at controlling plants because they eat more than older fish.

[Alice In TX/MO]

Do a google search on wind powered pond aeration. There are several options!