Where have the fish gone?

[corrigannick]

Hi there.
I have a fairly large, deep pool to pond conversion in Sydney Australia. Plenty plants, a pump to give flow and a solar aerator. I have about 25 Comets and Subunkin that have been in for about four months now and always came to the suface to feed and could often be seen having fun around the pond all in one big gang. There is only visibility for the first couple of feet, then the tanins and algae make it dark, which I do not mind at all. There are trees all around the pond, so undoubtably leaf material build up on the bottom.
It recently rained heavily and non stop for over two weeks here and the temperature was low as it was winter (but well above freezing), since then I have hardly seen any of the fish.
For two whole weeks I saw non at all. For the last two weeks I have seen a group of five and two individuals. No bodies have floated to the surface. I have tested the water, no problems in nitrates or ph.
Where have they gone?
a) most died after some agent was washed in?
b) they have decided that the deep plants and leaf mould is nicer than the cheap fish food I give them?
c) they were freaked out when I tried to scoop lots of leaf mould up and have never forgiven me?

I would really appreciate any help and ideas you wonderful people have!

Nick

 

[tbendl]

Hi corrigannick, I don't have fish so I'm not familiar with their peccadilloes but maybe they got spooked by something and are just freaked out or if the water temp got really cold at the top and it is warmer at lower depths they may be staying warm and getting ready for winter. Good luck, I hope you didn't have predator come to the pond, although with the depth and sloping sides of a pool convert, it sounds unlikely.

 

[corrigannick]

Thanks T!
It may be a temperature thing, but I thought that would only be in harsher climates. The air temperature went down to about 50f (10c) - but the rain was not very cold. I should get a thermometer I suppose!

 

[tbendl]

I would check that. If the temp was that cold and rained for that long it had to have replaced some of your water in your pond making the top colder I would think, especially if it rained for 2 weeks. I am sure people with way more fish experience than I have will jump in and may have a better idea.

 

[dieselplower]

I would surely get a thermometer as the water temperature is much more important than the outside temperature. I would also be interested in knowing the ammonia and nitrite levels, which are much more important than nitrate.

 

[corrigannick]

I would also be interested in knowing the ammonia and nitrite levels, which are much more important than nitrate.

Thank Dieselplower.
I took a water sample to the fish store and they ran tests for PH, ammonia and 3 others. Everything was normal. Would nitrite be on their standard battery of tests?

 

[dieselplower]

Thank Dieselplower.
I took a water sample to the fish store and they ran tests for PH, ammonia and 3 others. Everything was normal. Would nitrite be on their standard battery of tests?

Honestly I dont know. It should be.

 

[corrigannick]

Oxygen levels have to be high with the pump and splashing rain.

 

[Dave 54]

Hi Nick perhaps this may well be the answer to your question my friend :-

•
During the warm spring and summer months, we receive an increased number of phone calls regarding sudden fish kills in ponds. The typical history includes observing a very large number of fish dead in an otherwise normal pond following a rainstorm or summer thunderstorm. Usually the owner is very concerned that the fish may have died due to "run-off" of farm chemicals into the pond. Most of the time, these fish kills are a result of a phenomenon known as "pond stratification." Pond stratification is somewhat of a misnomer, since the stratification can also occur in lakes, creeks and some rivers. The stratification leads to a catastrophic depletion of oxygen which almost always results in a very high mortality of aquatic animal life within 24-48 hours following the "de-stratification."
The scientific reasoning behind this phenomenon of pond stratification relates to the temperature of the pond. In the early spring, while the temperature of the pond is still relatively low, the dissolved oxygen is uniformly distributed throughout the pond. As the atmospheric temperature increases, the pond begins to stratify, that is, become layered, with the surface water becoming warmer and lighter while the cooler and denser water forms a layer underneath. Circulation of the colder bottom water is prevented because of the difference in densities between the two layers of water. Dissolved oxygen levels decrease in the bottom layer since photosynthesis and contact with the air is reduced. The already low oxygen levels are further reduced through the decomposition of waste products, which settle to the pond bottom. After a rain, or any other event which disrupts the two layers, a "de-stratification" or "turn-over" of the pond occurs. This has the effect of releasing all of the dissolved oxygen from the upper layer of the pond into the atmosphere, hence, a catastrophic oxygen depletion.
Once stratification of a pond occurs, there is nothing that can be done to alleviate the situation. However, pond stratification can be very easily prevented by the use of supplemental aeration. Aerators come in all sizes and shapes as well as different power sources, i.e., tractor p-t-o, electrical, mechanical, etc. It is important to aerate the pond properly, i.e. match the size of the aerator to the pond, since over-aeration is wasted and may even lead to oxygen supersaturation, known as "gas-bubble" disease and under-aeration will not prevent stratification.
In those cases where we suspect catastrophic oxygen depletion, all other possible pathogens including bacterial, viral, parasitic agents are eleminated from the differential diagnosis list. However, the history of several days to weeks of warm weather followed by a sudden rainstorm are highly suggestive of this condition. If you suspect that you are dealing with a pond turn-over situation following pond stratification, it is imperative to have the pond owner take a water sample and have the dissolved oxygen (DO) concentration evaluated immediately. This water sample should be collected in a clean glass jar or bottle with a screw-top lid and should be completely filled by completely submersing the sample and container and placing the lid on the container while it is still under water.

Perhaps your goldies have died and been snaffled up by the side of your pond by the wildlife that abounds down under or the fish are dead on the bottom , it certainly fits with the rain you've been having and I think its your spring to our autumn it does fit with what you have said though however dead leaf should always be removed from the bottom of any pond its a cause of many ills for our fish and as such the pond should always be cleaned prior to winter which by my calculations you guys have just had.
Many folks on this forum including ourselves always net agaisnt leaves and clean the bottom of their ponds by pond Vacuum
Note this sentence :- The already low oxygen levels are further reduced through the decomposition of waste products, which settle to the pond bottom

Dave

 

[corrigannick]

Hi Nick perhaps this may well be the answer to your question my friend :-
Dave

Thank you so much, Dave.
Just after the rains started I did a major scoop out of seeds, leaves and branches from the bottom of the pond, this would have certainly provoked a sudden de-stratification, and given it had been cloudy for a while the solar aerator was idle.
I will know in the next couple of weeks if they are all hiding in the depths once the water warms up or if they have all left the pond.
If they have gone, I will work out a better aeration plan and maybe do the leaf matter clean up more often before I re-stock.
This is why I went for goldfish before investing in Koi!
Cheers
N

 

[Dave 54]

Thank you so much, Dave.
Just after the rains started I did a major scoop out of seeds, leaves and branches from the bottom of the pond, this would have certainly provoked a sudden de-stratification, and given it had been cloudy for a while the solar aerator was idle.
I will know in the next couple of weeks if they are all hiding in the depths once the water warms up or if they have all left the pond.
If they have gone, I will work out a better aeration plan and maybe do the leaf matter clean up more often before I re-stock.
This is why I went for goldfish before investing in Koi!
Cheers
N

Nick pond and filter maintenance are a must when it comes to koi keeping and fish keeping in general if looked after propperly goldfish will live upto 40+ years koi more so at 80+ years we had two 27 year old koi up till last moth sadly one of them passed away according to our club health official of old age however this was a koi that did not have a very good start in life and was recued by us from a 2ft tank with an agressive oscar as a tank mate the net result is it was stunted at 6" in length the other is still going strong at 27" .
May I suggest you check out our library of koi/koi health books etc and perhaps study into it some more so that nothing bad happens to them to put you off such beautiful fish :-

https://www.gardenpondforum.com/threads/our-fish-koi-health-library-with-reviews-of-each-book.10498/

Dave

 

[corrigannick]

Hi Nick perhaps this may well be the answer to your question my friend :-

However, pond stratification can be very easily prevented by the use of supplemental aeration.
Dave

I have just been thinking about the large pump that is still attached to the pond that used to filter the chlorinated water. If I run this for an hour a day on circulate (not filter) it should ensure that stratification does not occur. What do you think?

 

[Dave 54]

I have just been thinking about the large pump that is still attached to the pond that used to filter the chlorinated water. If I run this for an hour a day on circulate (not filter) it should ensure that stratification does not occur. What do you think?

Once you have cleaned the leaf mulch out of the pond plain old airstones supplied by a pond air pump would circulate the water in an upwards cycle but those leaves need to come out pronto my friend .


Dave

 

[corrigannick]

Once you have cleaned the leaf mulch out of the pond plain old airstones supplied by a pond air pump would circulate the water in an upwards cycle but those leaves need to come out pronto my friend .


Dave

The reason that I converted it from a swimming pool is because there are too many trees around and no mater what season there is bark, leaves, branches or seeds falling in. The only way to keep it debris free was having a professional pool company use their vacuum filter every week. The aim was for lower maintenance! There is no way that it will ever be free of debris, particularly around the structures I have put in to give levels for the plants. Is there not some level of organic decomposition that is not harmful if there is good water circulation?
I have a small water pump with basic filter on 24/7 that gives some circulation from deep to surface and am now wondering if I'd be better with an electric air pump rather than relying on solar. Dave, you are a gem.

 

[Dave 54]

Perhaps if you contact this net making company in the UK they can design then ship you out a custom built net mate :-

http://www.norfinenets.co.uk/nets-online.php?category0=33893541

We use the 6 mm hex mesh , you can still see the koi through it infact you hardly notice it after a while , we net against leaves and peditors like herons it uses a bungee strap across the centre and if you could drill in a number of small posts with a track for the net to slot into a bungee strap the entire circumfrence or what ever shape your pool is they will cater for it .

Thanx for the compliment mate but you dont have to thank me I'm just happy to help a fellow fish keeper

Dave