Unexplainable mass tank die off

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The GingerFishman

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Original poster
Feb 13, 2019
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Quincy, MA
Hi all,

I'm completely befuddled right now. One of my planted tanks has just begin a cross species mass die off. I've lost 20 fish out of my 100 gallon tank so far and I expect the remaining few will be dead by the end of the weekend. In my 30 years keeping fish I have never, ever experienced anything like this and I can't even figure out how to diagnose it.

Symptoms: Fish become shy, isolate themselves in corners or other quieter areas of the tank, breathing becomes rapid, then boom, within a few minutes to a few hours they're dead. I've woken up each morning this week and found fish that ate the night before and were entirely healthy, either floating dead at the top or dead on the substrate. I literally just watched my female Ram/Electric cross hybrid go from seemingly fine and displaying to a male to sinking slowly and swimming sideways eventually falling to the bottom and dying all within 1 hour.

I've tested the water numerous time, no ammonia, no nitrites, ph is where it usually is about 6.0 and I've done anywhere from 75% to 35% water changes each time it happens and it doesn't help. I thought perhaps the tank water rose to be much too warm since my house is so hot right now, as it did reach 85% but angels and rams are supposed to be able to handle the heat anyhow. I did change water with cool water each time to bring it back down to 77, and it slowly rises back up to 81 now that it's cooled off a little bit recently.

The fish exhibit no noticeable sign of disease, no streaks, no sores, no fungus, literally nothing. The only thing I can think of was that I put 3 Black Mollies in last week to take care of a Hair Algae issue (which they did) but one of them was a little male who looked a bit skinny to me but he was eating and seemed fine. The only thing I can think of was that he had some sort of virus and now the whole tank is contaminated. That seems highly unusual to me though. I got them from my trusted LFS and normally I select the fish I want but I let the kid who usually gets my fish just catch them and bag them up while I was talking to the owner and he know I always select plump healthy looking fish, so I didn't realize he was thin until I got home. I wish I had just taken him back at that point but I was crunched for time. Unfortunately my place is small and I don't have the space for a Q tank but I've literally never had issues - certainly not like this.

Either way, all of the fish that are dying aren't getting skinny before dying, they literally feed and seem healthy the night before then poof - instantly dead.

Also, the tank has several sponge filters running it and HOBs so the waterflow and aeration is fine too.

None of my other tanks are having any issues, so I know it's not like something happened to my water source either.

Any ideas at all what might be going on???

Thanks,

Mark
 
Apr 2, 2002
2,175
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51
New York
There are some virulent diseases that kill fast, even before there are not many symptoms showing before things go really wrong. Some strains of columnaris are able to cause this. If this is a virulent disease, be careful not to transfer it to other tanks.There is also the possibility of a contaminant getting into the water. This is often the cause of a rapid massive die off in a tank.

You should have a Q tank. This doesn't help with the current problem, but it will help avoid a similar mishap in the future. I have only had to deal with ich twice in 1+ years and across about 20 tank. Both times the ich came in with new fish. One time it was in a Q tank with store bought fish and the other time (with no Q) it killed a few of the fish already in the tank before I got it under control.
 

the loach

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Aug 6, 2018
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It has all the signs of a virus and not Columnaris. It's not likely to be ammonia, but it could be nitrite especially if the tank isn't planted.
The most surprising thing to me is that you add black mollies to a tank with pH 6. It's not a good idea to mix fish from very different biotopes together. Are the mollies still alive? They can carry viruses and bacteria for which they are immune but are deadly to other fish.
There could be issues with contaminants in the air or in the tank though. And did you put the water which the mollies came in in your tank?
 

FreshyFresh

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Jan 11, 2013
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Mark, sorry about your issues here!

It doesn't even have to be some super nasty virus or bacteria. It just has to be something your long established tank has never been exposed to before and doesn't have the means to defend against it.

Is your tap water that acidic? (pH of 6.0)

What is your normal water change frequency and amount changed? To me it almost sounds like a drastic pH swing in the tank and the almost instantaneous death resulting from that.

Only other thing I can think of is a faulty heater leaking current into the water column.
 

forse

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Nov 7, 2018
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Enrique
Are you adding CO2 to this planted tank? I feel worried about drastic and constant pH swings as FreshyFresh mentioned.
 
Apr 2, 2002
2,175
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51
New York
Before getting into columnaris a bit deeper, I would like to make another point about pH. There are no hard and fast rules regarding how a large change will effect fish. I know that Altum angels can deal fine with a pH drop of 1.0 in under five minutes with no ill effects. I have seen it done and have done it myself. In this case the drop was from acid to much more acid. I doubt they would withstand a rise like this from acid to neutral. I would not try this with most fish, however, some fish can handle a big pH swing. In my experience Ihere is a greater danger in a similar degree of change in TDS than from pH.

Just an FYI- the most virulent strains of columnaris will kill before there are any of the typical symptoms.Here is just one example:

Virulence assay of rhizoid and non-rhizoid morphotypes of Flavobacterium columnare in red tilapia, Oreochromis sp., fry

H T Dong1, S Senapin2,3, B LaFrentz4 and C Rodkhum1
1 Department of Veterinary Microbiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok,
Thailand
2 National Center for Genetic Engineering and Biotechnology, National Science and Technology Development
Agency, Pathumthani, Thailand
3 Center of Excellence for Shrimp Molecular Biology and Biotechnology, Mahidol University, Bangkok, Thailand
4 Aquatic Animal Health Research Unit, United States Department of Agriculture-Agricultural Research Service,
Auburn, AL, USA

Abstract
Numerous isolates of Flavobacterium columnare were previously recovered from red tilapia, Oreochromis sp., exhibiting columnaris-like disease in Thai farms, and the phenotypic and genetic characteristics were described. The objective of this study was to determine the virulence of two morphotypes (rhizoid and non-rhizoid colonies) of F. columnare and to determine their ability to adhere to and persist in red tilapia fry. The results showed that the typical rhizoid isolate (CUVET1214) was a highly virulent isolate and caused 100% mortality within 24 h following bath challenge of red tilapia with three different doses.
from https://www.researchgate.net/profile/Channarong_Rodkhum2/publication/276076175_Virulence_assay_of_rhizoid_and_non-rhizoid_morphotypes_of_Flavobacterium_columnare_in_red_tilapia_Oreochromis_sp_fry/links/5a8ec5d6aca27214055d9ceb/Virulence-assay-of-rhizoid-and-non-rhizoid-morphotypes-of-Flavobacterium-columnare-in-red-tilapia-Oreochromis-sp-fry.pdf

If one looks trhough the scientific literature on this disease you will find that it affects all sorts of fish, including ornamentals, and that it is believed there may be a many as 100 different strains. Different strains have different virulence and can be a threat to different species. One cannot assume that a problem is not related to columnaris just because there are no obvious external symptoms.

By way of personal experience I can report this disease is one which often affects newly imported wild Altum angels. I lost 20 fish inside if 36 hours from this. There were no white patches. Apparently normal fish would suddenly become lethargic and hang out on the bottom of the tank. Not long after they were at the surface struggling and then dead. I had all the recommended meds on hand to fight this disease but that did not matter. All of the other people who got fish from the same importer had a similar issue. Of 100+ fish bought by the group, I think 3 survived.

Finally, the only way to know for sure what got the fish would be a lab grade autopsy. So there is no way here to conclude that columnaris was the cause nor can it be ruled out.
 

the loach

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Aug 6, 2018
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Finally, the only way to know for sure what got the fish would be a lab grade autopsy. So there is no way here to conclude that columnaris was the cause nor can it be ruled out.
Once again I disagree with you; the LFS selling the fish would have the same problems. The OP could check or ask; they almost certainly won't have that problem. There is another logic argument against it as well, that I will leave up for guesses :)
Outside of a lab, though you do need basic biology/dissecting skills, you can do an autopsy of the deceased fish. If the spleen is whitish, it's almost certainly a virus, whereas with bacterial infections it will be dark to normal in color.

About the pH: the OP stated "ph is where it usually is about 6.0" from which I take there was no pH crash.
 
Apr 2, 2002
2,175
44
51
New York
the LFS selling the fish would have the same problems
1. We do not know if they did or did not.
2. We do not know if the store uses individual isolated tanks or a central system.
3. We do not know if they use different nets for tanks.
4. We do not know many things here.

you can do an autopsy of the deceased fish.
Lets run am informal poll. Anybody reading here please post if you have adequate tools to preform an autopsy on a small fish the size of a molly or ram. Please post here if you know how to identify and locate the spleen in any of your your fish.
 
Apr 2, 2002
2,175
44
51
New York
I should have included this in my post above.

I am ignorant. I cannot find which viral disease we might encounter in a freshwater tank that can kill off most or all of the fish (of a few different species) in a mater of a day or two and which will not cause any external symptoms one can see.

T the loach , please educate me as the which viruses can do this in fw tanks. It would help if you could link me to a study etc. which would provide detailed information on such a virus or viruses.

Thank you in advance for helping me learn.
 
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