Help - Cory's keep dying

[Tessa92]

Hi there,

I have an issue with my corys which started a while ago now. First noticed it when one of the them was acting strange - lethargic at first and resting in odd places, then rapid breathing and laying at strange angles/ on its side. After a few days this Cory died. There were no physical signs of illness at all. A few days later another Cory started acting the same way and died the next day. This has now killed 4 Cory's, one by one. All other fish in the tank seem completely fine, and the other Cory's at the moment seem completely fine.

Tank is 50 gallons and contains 8 cardinal tetras, 7 ember tetras, 1 BN pleco and 3 amano shrimp. There were 7 delphax corys, now 3.

Water seems fine, 0 ammonia and 0 nitrite and 15 Nitrate. 24-25 degrees Celsius. Cory's are fed a mixture of wafers, bloodworm and pellets and seem to eat OK. Most of the Cory's that died were 2-5 years old and seemed healthy until recently.

Any idea what might be causing this and what I can do?

 

[HoldenOn]

Hi there,

I have an issue with my corys which started a while ago now. First noticed it when one of the them was acting strange - lethargic at first and resting in odd places, then rapid breathing and laying at strange angles/ on its side. After a few days this Cory died. There were no physical signs of illness at all. A few days later another Cory started acting the same way and died the next day. This has now killed 4 Cory's, one by one. All other fish in the tank seem completely fine, and the other Cory's at the moment seem completely fine.

Tank is 50 gallons and contains 8 cardinal tetras, 7 ember tetras, 1 BN pleco and 3 amano shrimp. There were 7 delphax corys, now 3.

Water seems fine, 0 ammonia and 0 nitrite and 15 Nitrate. 24-25 degrees Celsius. Cory's are fed a mixture of wafers, bloodworm and pellets and seem to eat OK. Most of the Cory's that died were 2-5 years old and seemed healthy until recently.

Any idea what might be causing this and what I can do?

This happened to one of mine. No clue what it is.

 

[Tessa92]

This happened to one of mine. No clue what it is.

Did it stop after one? Unfortunately it seems to be killing all of mine one at a time

 

[HoldenOn]

Did it stop after one? Unfortunately it seems to be killing all of mine one at a time

So far it's only been one. Sorry about your loss . @NCaquatics is the main person for corydoras here.

 

[HoldenOn]

Ah. It seems we both have internal parasites. If you look at my thread "I'm going to loose another" you can see recommendations.

 

[Retired Viking]

I agree with @HoldenOn sounds like internal parasites, have any other fish shown any signs or strange behavior?

 

[CassCats]

The heavy breathing also sounds like this could be gill flukes.

Did you add any new fish lately? Within the last few weeks or maybe month?

Anything change at all in their environment?
Is there any other fish showing any unusual new behaviors to you?

Cories are sensitive to chemicals, did anything get sprayed or contaminate the tank? (I've just been through a situation where this had to be asked too)

 

[itiwhetu]

What is the pH of your water?

 

[Tessa92]

The heavy breathing also sounds like this could be gill flukes.

Did you add any new fish lately? Within the last few weeks or maybe month?

Anything change at all in their environment?
Is there any other fish showing any unusual new behaviors to you?

Cories are sensitive to chemicals, did anything get sprayed or contaminate the tank? (I've just been through a situation where this had to be asked too)

No new fish or anything when it started happening, maybe a couple of new plants but nothing major.

All other fish are acting normal, look healthy and haven't lost any.

I'm usually very careful and don't use any chemicals in that room but it's possible. They have died one by one over a long period of time now though.

 

[Tessa92]

What is the pH of your water?

Water is pretty soft here and pH usually sits around 6.5

 

[Gypsum]

I had a shoal of c. trilineatus that exhibited similar symptoms. One by one, they got lethargic, would lie at odd angles or fail to swim, and then drop dead. At first, I tried treating it with various things -- anti-fungal, anti-bacterial, malachite green -- but if you don't even know what you're treating, it's pretty useless. And it was. By the end, I would just euth the fish straightaway if it started lying on its side. Seemed more humane than quarantining it and throwing random chemicals at it. My slow c. trilineatus extinction took place over a period of months.

I have other shoals of corys -- different species -- who are absolutely fine. The c. schulzeii and CW045 were living in the same tank as the trilineatus, and they remain happy and healthy (knock on wood). Water parameters were (and are) 0 for ammonia and nitrates/ites. I have a similar PH to yourself. At the time, I posted on the Corydoras World Facebook group, and their cory experts suggested that it could have been an issue with the stock. They could have suffered some damage at any point in their transport to the fish shop, or they could have just been weak due to underlying issues or overbreeding.

That said, I didn't think c. delphax was that common in the hobby. According to the data on PlanetCatfish.com, which of course is limited to people who've registered themselves as keepers on PlanetCatfish.com, it's not even in the top 25 most kept species, whereas trilineatus is 6th on that list. Still, something could have happened to yours between wherever they were caught/bred and your tank.

 

[Tessa92]

I had a shoal of c. trilineatus that exhibited similar symptoms. One by one, they got lethargic, would lie at odd angles or fail to swim, and then drop dead. At first, I tried treating it with various things -- anti-fungal, anti-bacterial, malachite green -- but if you don't even know what you're treating, it's pretty useless. And it was. By the end, I would just euth the fish straightaway if it started lying on its side. Seemed more humane than quarantining it and throwing random chemicals at it. My slow c. trilineatus extinction took place over a period of months.

I have other shoals of corys -- different species -- who are absolutely fine. The c. schulzeii and CW045 were living in the same tank as the trilineatus, and they remain happy and healthy (knock on wood). Water parameters were (and are) 0 for ammonia and nitrates/ites. I have a similar PH to yourself. At the time, I posted on the Corydoras World Facebook group, and their cory experts suggested that it could have been an issue with the stock. They could have suffered some damage at any point in their transport to the fish shop, or they could have just been weak due to underlying issues or overbreeding.

That said, I didn't think c. delphax was that common in the hobby. According to the data on PlanetCatfish.com, which of course is limited to people who've registered themselves as keepers on PlanetCatfish.com, it's not even in the top 25 most kept species, whereas trilineatus is 6th on that list. Still, something could have happened to yours between wherever they were caught/bred and your tank.

Yeah I've considered stock maybe being the issue. They were bought at different times though with the oldest being about 5 years old - but still from the same shop so I guess it's possible.

I've considered treating the tank but like you said its hard when you don't know the issue and I don't want to kill the shrimp and potentially stress other fish in the process
Its a shame, I love corys but I'll be scared to buy more incase it happens again.

 

[Gypsum]

My c. trilineatus were bought from the same shop at different times.

Only other thing I got is oxygen levels. Is there enough surface disturbance and flow in your tank? Could there be anaerobic pockets somewhere? Do you vacuum the substrate and are they on sand?

I've got powerheads everywhere now and have had less issues with corys since installing them, although I mainly got them to keep rheophilic species of plecos.

 

[Tessa92]

My c. trilineatus were bought from the same shop at different times.

Only other thing I got is oxygen levels. Is there enough surface disturbance and flow in your tank? Could there be anaerobic pockets somewhere? Do you vacuum the substrate and are they on sand?

I've got powerheads everywhere now and have had less issues with corys since installing them.

Flow is decent and oxygen should be ok, have an airstone on periodically. They are on sand which does get vacuumed but its possible there are anaerobic pockets in the hard the reach/planted areas as the sand is quite fine and relatively deep. Could that potentially be the issue?

 

[Gypsum]

I run airstones 24/7 in all four of my tanks. Two of the tanks have powerheads as well as lots of filtration. As I understand it (and I'm not expert), increasing flow and surface agitation can help with oxygenation and prevent pockets of bad stuff building up by keeping water moving throughout the tank, even in the awkward corners. Quite frankly, there's a lot of complicated science around oxygenating fish tanks, which I found baffling. But the verdict amongst people breeding Hypancistrus species of pleco, which demand highly oxygenated water, seemed be either run a powerful HOB filter, an HMF filter, and/or powerheads.

Obviously not all fish can cope with powerheads, but tetras should be okay.

I have read that sand should not be deeper than 2". I think that's the rough number. If it's too deep, anaerobic pockets can form under the substrate.