pond koi die off

[lindamarie]

We had large koi in our pond along with small goldfish. Two days ago we found all of our koi dead, but small gold fish alive and well. The pond water got very dark and a lot of oak leaves floating. Is there a poison in the leaves that could cause this or some sort of lack of oxygen. We have had the koi in there for years, they were all bought at the same place and time and all died at same time. The gold fish have only been in there about 6 months.

We had something like this happen about 12 years ago, all the catfish, sunfish.
We only had 4 large koi. Anyone else ever have this happen or any ideas why.

[Buffy in Dallas]

Sounds like low Oxygen levels but check the Ph level just in case. I would put a small fountain in the pond to oxygenate the water. I don't know if oak leaves are a problem but you might want to try skimming the oak leaves out.

Last time this happened was it in the early winter too?

Does your pond collect run off from off your property? Farm run off?

[K.B.]

While still in the carp family, koi are generally considered less hardy than some other types of carp (common goldfish, comets, etc...).

The tannins from the oak leaves probably aren't helping any, but it sounds like they would have been through that experience before if they've been there for several years.

As Buffy stated above, pH, dissolved oxygen, fluctuating water temps, ammonia/nitrate/nitrite concentrations, and other factors can all play a role in stress on the fish.

How large is the pond (natural, artificial)? Is there a filter or any mechanical aeration?

[7thswan]

Oh, I'm sorry about your Koi. I moved all my goldfish and one Koi into a trough in my hoophouse. Set up 2 bubblers. The next morning went out and could not see the Koi,(he was big). There he was dead on the floor. I guess he got spunky with being moved and jumped out. Here, I did all that moving and such just for the Koi.

[TRAILRIDER]

Sounds to me like a spike in ammonia/nitrite levels from the leaves (or something else?) decomposing in the water all at once. The koi being larger and less hardy as stated before are more susceptible to the toxins. Plain old goldfish can survive a lot. Some fish stores will do a water quality test for you (we used to test water for free when I worked in a pet store) and that will tell you for sure. But you have to do the test right away as the ammonia turns to nitrite then nitrite turns to nitrate. Ammonia is extremely toxic to fish. Anyway, sorry for your fish loss. Good luck.

And yes, 7thswan, I've had the same thing happen to me. Fish jumping is common. Did you know if you catch them early enough you can pick them up off the floor and hold them under water. You can move them in the water making water move through their gills and its like artificial respiration. I've brought a few back that way. Unfortunately when you find them they are usually too far gone : (

[lindamarie]

We have no run off that would have any chemicals, etc. It could be the oxygen, we are going to try adding more water plants. Pond is over 8 ft deep, fed by underground spring, manmade at least 70ft in diameter. This is the first winter that any fish other than koi have been in there. Always newts, frogs, box turtles and the occasional snake in the summer.

[mnn2501]

Did it get too cold? theres nothing telling us where you are.

[paradox]

I doubt this is your issue, but just a thought for others who might have dogs. We had a lovely pond and some really big koi we had for years. My Mom brought over her dog during a visit. The dog went swimming in the pond and had some of that spot on flea and tick medicine on her back. Killed every single fish we had.

[rover38]

You said there were a lot of oak leaves floating in the water and the water turned dark - Oak leaves contain tanic acid that would leach into the water - also turns it brown

[lindamarie]

Sorry, it used to say I was in wv. They died before our cold snap.

[badlander]

Koi are such beautiful little divas hyper sensitive to low O2, drastic changes in temp and other environmental changes. I had 6 beauties in my pond. It was the right depth, had a waterfall and bubbler going. Everything was right until the temp hit 90 and stayed there for about 2 weeks. Every koi died on me. I figured I lost given they were 14 inches each, about 400-500 dollars worth of fish in that heat wave. I was physically sick.

The tannin would decrease water quality which could stress and kill them, but they could have also succumbed to a parasite or bacterial infection due to the poor water quality. Were you able to examine their remains? Were there any 'cotton' spots on their fins or tail indicating a fungal infection? Any signs of infection or parasites?

The one thing I learned from my experience is that they need LOTS of pond space, more depth than common comets or fan tail shubunkins, excellent water purity and clarity along with more aeration than the common gold fish. I would definitely net your pond over in the future to prevent leaves from getting into it and I would carefully calculate how many Koi your pond will support. Better to under populate than over as over population will definitely cause stress in extreme water conditions.

So sorry about your loss. Any one who has ever had Koi can sure sympathize with you. I'm contemplating dropping a liner into a 35X35 foot lagoon I have on the farm and adding some common comets to it. I won't try Koi again, not with the raccoons and varmints we have around us. You might want to check with a local pond supplier/designer you might have around you. They are usually eager to offer assistance and answer questions. We know one who has worked it into his greenhouse/garden center. The whole area around his greenhouses is filled with beautiful ponds. Good luck hunting down the cause of your die off.

[fishhead]

Generally a sudden die off is the result of oxygen depletion. Mortality from disease or high levels of ammonia or nitrate are more spread out over time.

Cool water holds more oxygen than warm water and cold water holds more oxygen than cool water plus the cooler it gets the less oxygen the fish need.

[Paquebot]

The dark water equalling dead fish could be the same as what happens to me annually. I used to claim that I am one of few who lose goldfish to squirrels. An apple tree shades the pond but there's a black walnut tree next to that. Squirrels sit in the apple tree and husk walnuts. The husks fall into the water and the goldfish are soon belly-up if I don't replace most of the water.

Martin

[swamp man]

Dang....sorry you lost your fish. Like Rover, Tanic acid would be my first suspicion. I built a koi pond for some customers years ago, and they kept happy, healthy fish for quite a while...'til they all croaked at the same time. I went to check it out, and they had apparently started slacking on emptying the skimmer and the mesh filter on the waterfall, which were both full of....yep....oak and maple leaves.

[Paquebot]

Tannin is not considered toxic to fish. In fact, it is used as a natural means to lower the pH in aquariums. If walnuts were not involved in the koi pond, then I would suspect an accumulation of decaying leaves at the bottom using up most of the oxygen. Just as with juglone poisoning, it's the biggest ones which die first.

Martin

[TRAILRIDER]

Tannins are not toxic to fish ,no. But I believe the tannins would naturally lower the Ph. And carp prefer a higher Ph so that would cause some stress. If there is ammonia in the water due to decomposition (first from leaves then from fish die off) the ammonia rise would deplete oxygen too. Could certainly be a combination of stresses.