Denison barbs suddenly died

[agordonny]

Three of my four denison barbs suddenly died overnight and the fourth is dying. They were in a 75 gallon with a seven, goldfish, and for bristlenose. The tank was healthy and steady for five years. I recently separated one barb and treated him for what looked like a fungus on his tail. He seems to heal and I returned him. All was good for a week and now the barbs are dead, but everyone else looks fine. Any ideas? I separated the remaining barb and did 50% water change. Levels are good. My nitrates are high, but they always are- no sudden change

 

[Andy Sager]

Three of my four denison barbs suddenly died overnight and the fourth is dying. They were in a 75 gallon with a seven, goldfish, and for bristlenose. The tank was healthy and steady for five years. I recently separated one barb and treated him for what looked like a fungus on his tail. He seems to heal and I returned him. All was good for a week and now the barbs are dead, but everyone else looks fine. Any ideas? I separated the remaining barb and did 50% water change. Levels are good. My nitrates are high, but they always are- no sudden change

How high is high?
Usually, when all or most of a single specie dies in a community tank, that's a sign of water issues. The water may be okay for some species but not others. If it were just an illness but it was only affecting one specie, that specie would be stressed which would again lead to an environmental issue. A 50% water change can be way too much change for Dennison's Barbs. I have a feeling that is your cause. With those fish, it's better to do smaller more frequent water changes than one large water change. They don't handle change very well.

Hope this helps.

 

[agordonny]

Thank you so much for your response!
I don't have the exact nitrate ppm with me, I'm at work. It has been steady for years though. The tank, with the barbs, was established mid 2018. I've been told that a consistent level is ok.
I only did the 50% change once they were all dead already. Typically I do more like 15%-25% weekly. What do you think of that?
These fish were huge and healthy and active.
It's heartbreaking.
Thank you for any information and thoughts!

 

[Andy Sager]

Thank you so much for your response!
I don't have the exact nitrate ppm with me, I'm at work. It has been steady for years though. The tank, with the barbs, was established mid 2018. I've been told that a consistent level is ok.
I only did the 50% change once they were all dead already. Typically I do more like 15%-25% weekly. What do you think of that?
These fish were huge and healthy and active.
It's heartbreaking.
Thank you for any information and thoughts!

Okay, I read it that you did the water change and then they died. Big difference. A 15%-25% weekly or even twice weekly should be fine. As stated, Dennison's do not like quick changes to their aquatic environment.

Here's the thing with nitrates. They are not totally harmless. They are less harmful than ammonia and nitrites and need to be in lower amounts to maintain that harmlessness. With long term exposure to high nitrates, nitrate gets into the fish on a cellular level and over time, causes organ damage. This is why a level under 40 PPM and ideally more closer to 0 is what's recommended. The good news is that fish can recover from nitrate " poisoning" by having good clean water so that it flushes out the fish's cells with good water.
This is from PetMD:
The Potential Dangers of Excess Nitrate Levels
Sure, you've been told so many times that nitrate is harmless. A lot of fishes can tolerate brief exposures of up to 550 ppm. Chronic exposure, on the other hand, can indeed be damaging, even at much lower levels of exposure.

Over time, at just 30 ppm, nitrate can negatively impact cell development in both fishes and invertebrates. Lethargy, poor color, poor immune system and weakened feeding response are all signs of nitrate poisoning.

Most professional aquarists contend that nitrate concentrations should never exceed 20 ppm but are much more safely maintained below 10 ppm.

Still, nitrate concentrations of just a few parts per million can lead to massive algal blooms. These may occur as either planktonic (e.g., "green water") or benthic (e.g., film or slime) blooms.

So while consistent parameters is good, consistent correct parameters is what's necessary for long term health.

Now, with all that said, when a group of the same specie all die in a tank within a day or two of each other, that usually says something in the water did not agree with them. In your case, it may have been the nitrates? May have been a change in the oxygen level in the water? May have been a dramatic temperature change? Unfortunately, to determine if any of these were the cause, you would have needed to test the water when you found the fish dead. Other than that, it's really all guesses without an actual autopsy by a professional. Let's start tho with the actual nitrate level.

 

[agordonny]

I tested the water when I found the dead fish. I'll post the parameters when I get home tonight. Thank you for the information on nitrates

 

[agordonny]

I just pulled up the API test kit key and see my water tested between 40 & 80 ppm nitrates. I will continue working on bringing that down.
I'm stumped.
I don't see why O2 levels would have changed and the temperature is consistent.
Obviously something didn't agree with the barbs overnight though

 

[Andy Sager]

I just pulled up the API test kit key and see my water tested between 40 & 80 ppm nitrates. I will continue working on bringing that down.
I'm stumped.
I don't see why O2 levels would have changed and the temperature is consistent.
Obviously something didn't agree with the barbs overnight though

Correct, something got to them.
While the 80 PPM shouldn't be a real issue for the short term, it may have had something to do with the issue long term. How long did you have the Barbs at the nitrate level?

 

[agordonny]

They had been in that tank for over five years with consistent water parameters

 

[Andy Sager]

They had been in that tank for over five years with consistent water parameters

They only have an average lifespan of 5 years +/- so maybe it was a Murder/ Suicide pact? But seriously, it's not usual for all of a specie to just die for no reason. If you've had them for 5 years at least, you should consider it a success tho.

I have another thought, could something have startled the fish and gave them a heart attack? I ask because a former Pet Shop boss of mine was at the local wholesaler and when he put a net into a tank of a fish known to be easily spooked, he said the whole tank of fish just laid down and freaked out. He said it was freaky because they were just laying on the bottom shaking and twitching. According to the wholesaler, they never recovered. So just another possibility to consider.