The wife has a recirculating system in which she raises Pla Duck. In the last few days we are getting some fish dying off. I'm thinking its the heat doing this, because there is nothing physically wrong with the fish. We do about 20% water changes which include cleaning filters daily.

Sorry, but are "pla duck" catfish, tilapia or something else?

Anyway, check the following:

1. Are you using city water for your water changes? If yes, you could be clorinating your fish.

2. Are the fish biting the surface of the water especially in the early morning. Or do they eat better in the afternoon than they do in the morning? If so then there is not enough oxygen in the water.

3. Check your ammonia levels. If they are OK, check your nitrite levels. You can get cheap color test kits from your local pet store for both of these.

If there are no problems with the water quality, then start looking at the fish more carefully. Begin with the gills. You can compare a healthy fish and a newly dead one to see if you can see any differences.

Edited May 10, 201115 yr by Pacificperson

If it is government water supply the the chlorine is the killer. Happens here too.

Sorry, but are "pla duck" catfish, tilapia or something else?

Anyway, check the following:

1. Are you using city water for your water changes? If yes, you could be clorinating your fish.

2. Are the fish biting the surface of the water especially in the early morning. Or do they eat better in the afternoon than they do in the morning? If so then there is not enough oxygen in the water.

3. Check your ammonia levels. If they are OK, check your nitrite levels. You can get cheap color test kits from your local pet store for both of these.

If there are no problems with the water quality, then start looking at the fish more carefully. Begin with the gills. You can compare a healthy fish and a newly dead one to see if you can see any differences.

We are using well water. They have enough oxygen. The bio-filters take care of the ammonia. The fish look fine.

The problem seem to have been corrected, by not feeding them in the afternoon for a couple of days. We now only feed to saturation in the morning, afternoons is when the filters are cleaned, and water changes occur. We then feed lightly which seem to keep it in better condition till the next day. Pla Duk are a type of catfish which can breathe air, should there not be enough oxygen in the water.

Good. Some more possibilities: your cleaning technique for your biofilter is off and you are building up ammonia overnight, there is a thing called gas bubble disease that happens when you add water from a very deep well directly to a fish tank.

And finally, I think that you can probably kill Clarias catfish with low oxygen. There is an old study by Diana et al. 1988 in which they estimate a daily mortality rate of 1/1000 at a DO above 1 and a daily mortality rate of 9/1000 at a DO below 1 in concrete tanks in Thailand. Your slowing down the feeding rate in the afternoon may be causing the system to need less oxygen overnight when it is naturally at its lowest.

Edited May 11, 201115 yr by Pacificperson

I got 55000 pladuck fishes,not in concreet thanks ,beter in a naturel pond.

My water its green and the oxygen levels ore what ever i not chek,everythink goes fine.

Fore my oxygen levels keep high ,i use a simpel inlet outlet pump 2 HP.

Now i say maybe shomtink chek your food size.

And make you feed a litle swet with water.

Good. Some more possibilities: your cleaning technique for your biofilter is off and you are building up ammonia overnight, there is a thing called gas bubble disease that happens when you add water from a very deep well directly to a fish tank.

And finally, I think that you can probably kill Clarias catfish with low oxygen. There is an old study by Diana et al. 1988 in which they estimate a daily mortality rate of 1/1000 at a DO above 1 and a daily mortality rate of 9/1000 at a DO below 1 in concrete tanks in Thailand. Your slowing down the feeding rate in the afternoon may be causing the system to need less oxygen overnight when it is naturally at its lowest.

Got between 8,000 to 10,000 fish in this system right now. Averaging 5 to 7 deaths per day. Probably due to cannibalism.

Good. Some more possibilities: your cleaning technique for your biofilter is off and you are building up ammonia overnight, there is a thing called gas bubble disease that happens when you add water from a very deep well directly to a fish tank.

And finally, I think that you can probably kill Clarias catfish with low oxygen. There is an old study by Diana et al. 1988 in which they estimate a daily mortality rate of 1/1000 at a DO above 1 and a daily mortality rate of 9/1000 at a DO below 1 in concrete tanks in Thailand. Your slowing down the feeding rate in the afternoon may be causing the system to need less oxygen overnight when it is naturally at its lowest.

Got between 8,000 to 10,000 fish in this system right now. Averaging 5 to 7 deaths per day. Probably due to cannibalism.

cannibalism oke ,but how big your fish??

And cannibalism you wil not see your fish again

how do you know that your fish go daeths

Good. Some more possibilities: your cleaning technique for your biofilter is off and you are building up ammonia overnight, there is a thing called gas bubble disease that happens when you add water from a very deep well directly to a fish tank.

And finally, I think that you can probably kill Clarias catfish with low oxygen. There is an old study by Diana et al. 1988 in which they estimate a daily mortality rate of 1/1000 at a DO above 1 and a daily mortality rate of 9/1000 at a DO below 1 in concrete tanks in Thailand. Your slowing down the feeding rate in the afternoon may be causing the system to need less oxygen overnight when it is naturally at its lowest.

Got between 8,000 to 10,000 fish in this system right now. Averaging 5 to 7 deaths per day. Probably due to cannibalism.

cannibalism oke ,but how big your fish??

And cannibalism you wil not see your fish again

And about welding water.

I dont know your aerea ore place that your stay ,but here welding water about 16 m deep you wil ghet 40 % salt water.

And how big its your conkreet thank for 10000 fish

how do you know that your fish go daeths

Good. Some more possibilities: your cleaning technique for your biofilter is off and you are building up ammonia overnight, there is a thing called gas bubble disease that happens when you add water from a very deep well directly to a fish tank.

And finally, I think that you can probably kill Clarias catfish with low oxygen. There is an old study by Diana et al. 1988 in which they estimate a daily mortality rate of 1/1000 at a DO above 1 and a daily mortality rate of 9/1000 at a DO below 1 in concrete tanks in Thailand. Your slowing down the feeding rate in the afternoon may be causing the system to need less oxygen overnight when it is naturally at its lowest.

Got between 8,000 to 10,000 fish in this system right now. Averaging 5 to 7 deaths per day. Probably due to cannibalism.

It sounds as if you don't need any more second guessing. Good luck.

Good. Some more possibilities: your cleaning technique for your biofilter is off and you are building up ammonia overnight, there is a thing called gas bubble disease that happens when you add water from a very deep well directly to a fish tank.

And finally, I think that you can probably kill Clarias catfish with low oxygen. There is an old study by Diana et al. 1988 in which they estimate a daily mortality rate of 1/1000 at a DO above 1 and a daily mortality rate of 9/1000 at a DO below 1 in concrete tanks in Thailand. Your slowing down the feeding rate in the afternoon may be causing the system to need less oxygen overnight when it is naturally at its lowest.

Got between 8,000 to 10,000 fish in this system right now. Averaging 5 to 7 deaths per day. Probably due to cannibalism.

cannibalism oke ,but how big your fish??

And cannibalism you wil not see your fish again

And about welding water.

I dont know your aerea ore place that your stay ,but here welding water about 16 m deep you wil ghet 40 % salt water.

And how big its your conkreet thank for 10000 fish

how do you know that your fish go daeths

UP

Hi Mellow...It's been a while mate, as usual, i need details,

1. Tank size ?

2. water level ?

3. I thought all you concrete tank were 80% roofed ?...no ?

4. Pla duk Big Oui or Lat Sia ?

5. Feed to satiation or do you hold back ? Feeding schedule, time and temperature during feeding

6. Stock rate per tank size ?

7. What remedies and supplement and how often ?

8. your regional weather pattern ?

Cheers