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Anybody know about pond fish?


Perkil8r
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I have a largely "wildlife" pond, about 8ft x 6ft x 30inch deep. When I moved in 4 and a bit years ago it was covered over and mostly empty, I uncovered it and let the rain fill it. I added some weed and a few plants and that was it until SWMBO decided she wanted some fish. We added 5 goldfish and they have been fine for 3 and a half years. They have had numerous babies and those babies have had babies and so on etc.


 


We hardly ever feed them, they feed on the critters in the pond and the whole thing looks after it's self quite nicely. Over the past 2 days though I have pulled out 5 dead fish and have another now floating on it's side but still alive.


 


We don't do anything to the pond, we added some snails and a couple of freshwater mussels a couple of years ago. Most of the other fish seem fine, some much smaller and some much bigger than the ones that seem to be dying. The ones that are dying are all very similar in size and colour so I am wondering if one lot of babies were born with a health problem? The fish are approx 1 and a half inches long and neither fat nor slim, just regular fish shape.


 


Any suggestions? We have plenty more but want to be sure it's nothing wrong with the pond. I might bring home a PH tester tomorrow from work just out of interest.


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It might be a bit of inbreeding. I keep tropical fish and there are plenty of cases of captive species developing problems due to a restricted gene pool. You've not mentioned any signs of disease such as bloating, raised scales, growths or coatings etc. You are right to get the water tested just to be on the safe side though. If you can, get the nitrates checked too.


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There are no signs of anything other than them being dead and on their side. The original fish now about 5 inches long and the last lot of babies appear to be fine. The rest are still there but keeping out of the way as they do most of the time in the winter. It's just this few who do look very similar.


 


Any idea what figures I should be looking for?


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Pond water should be close to 7.5, slightly more on the alkaline side won't be a problem. Nitrates should be close to zero. If you've got plants and algae, they should be keeping those levels down anyway. Have you got a pump or anything in there to oxygenate the water?


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Guest Libby's

Do you have a pump/filter?

If the fish have been breeding very well and you have lots more than originally it might be that you have ammonia build up in the water due to overstocking if you haven't got the water being filtered. The number of centimetres of fish per cm of pond surface may have been exceeded (not sure what the healthy ratio is in ponds - only tank fish) but if it's exceeded even with plants there could be a build up of toxins like ammonia or nitrates. Or simply not enough oxygen in the water to support all the fish.

I'm assuming you haven't had an new fish added from a shop or another pond that might have introduced disease?

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Thanks for the replies.


 


We have never had a pump in there, nor added any other fish other than the original 5.


 


We have plenty of oxygenating plants and weed in there. The only filters are natural such as the freshwater mussels, snails and suchlike.


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My pond is slightly bigger but you should be ok without a pump

My suggestion if there is no sign of disease is look to the air :o

Last time I had this it was a heron stomping about nicking fish

And stressing some of the others. If they are brighter coloured

And not black I would suspect one for this

Sheila

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I guess that is possible although a heron is a big bird and there isn't a clear flight path from any direction to the pond. Certainly worth adding to the list of causes though, mind you the cat hasn't been as hungry of late :bat:


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I'm going to take some pond water into work tomorrow and test it for oxygen, PH and Nitrate levels. Hopefully that might either highlight the issue or at least rule one or more out.


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I think you may need to test at home straight from the pond.

You can get test kits from local tropical fish place.

Not ute but think chemistry of water will change with time

Lots of small little microbe critters in water if you seal and

Take to work. Oxygen level may well drop.

Don't forget nitrite and ammonia as fish are much more sensitive

To these and pH

Edited by Sheila
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Oh forgot to add fish can tolerate quite high nitrate levels

If they get used to a slow increase. Most riggers and

The like have quite high concentrations the world over due to

Farming etc. it's the fast fluctuations they find difficult to

Adjust to

Sheila

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Mike if the water is low in oxygen then you should see the fish gulping at the surface. If the water has a nitrite or ammonia spike then you can often see the fish flicking against something like they have an itch. Also the fish often try to jump out of the water. Having said the above though the winter has been particularly dark so the weed you have in the pond may not be enough to oxygenate the water if your stocking levels have increased to an unsustainable level. From memory i think the rule of thumb is 1 inch of fish to 10 litres of water.

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I used to keep fish in a pond when I lived with Mum and Dad yonks ago. It does sound like you have too many fish for the space and it might be worth giving some of the smaller ones away to friends with ponds. Don't release them into the wild, as this is illegal but they won't last long anyway, being easy fodder for predators.


 


You could also try siphoning out some of the accumulated muck at the bottom of the pond. We did this regularly.


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