mass die-off

I have a 30 gallon that was, until Tuesday, over loaded with various corydoras awaiting new homes until my fishwall gets up and running. The tank is filtered by an Aquaclear 70 and an Eheim 2213. It housed a dozen or so corys of various types and some leftover ancistrus fry, and has for the better part of the year.

On Tuesday I did my weekly 30% water change and rinsed both the prefilter and the sponge of the Aquaclear. Almost immediately I started to see fish rolling over stiff as a board. I feared I had used water that was too cold, but the temp had only dropped 5 degrees. I use Prime as my dechlor.

By the time I got home from work yesterday, another half dozen corys had snuffed it. I ran some diagnostics and found nitrate at 10-20 ppm (admittedly elevated), slightly elevated ammonia. pH was 6.4. Performed a massive water change, and things seemed to calm a bit.

This morning, 2 more of the surviving 8 corys were dead. Noted that of all the casualties, several showed signs of fin rot, though the majority did not. There was no sign of rot when I fed and performed my nightly inspection on Monday. The last of my mighty herd of ancistrus appear completely unaffected.

The saddest part of this is that tank has been running largely without incident since I set it up in '95. Also, it housed my Mike Barber corys, the pride of my fleet.

Any ideas as to the cause? If it's time to tear this thing down and reboot, what's the sterilization procedure?

Blaise

Boy, that's awful. I don't have any suggestions as to the cause. I agree that the temperature change shouldn't have been a problem, and you used a good dechlorinator, and only cleaned one of two filters. Total mystery.

I will say that I've had some unexplained deaths of cory fry recently, including about 10 in a 20 gallon tank. The only possible cause I could identify was that the water was a little on the warm side. That's obviously not your problem.

They probably poisoned themselves from stress during the water change. Your water parameters are fine. Best thing to do is run lots charcoal to get the toxins out.

For Corydoradine keepers who may not be aware, these fish excrete a slimy toxin when they are freaked. They are difficult to ship because of this and there can be mass die offs in tanks with heavy population of corys and similar fishes.

Sorry, Andrew -- can you explain why cories would stress themselves to death during a routine water change??


You mention a slightly elevated ammonia. What is your nitrite?? When I've had issues post-water change it's always because of the nitrite. I've had unexplained nitrite spikes despite use of a dechlorinator. So much so, that I only used aged water for water changes. I realize this makes me overly paranoid, but since I've gotten a large trash can and keep water bubbling and dechlorinated for 24 hours before use, I do not have this problem. I also only rinse out filters in used tank water.

Sorry for the losses. that can be difficult.

Andrew said:

They probably poisoned themselves from stress during the water change. Your water parameters are fine. Best thing to do is run lots charcoal to get the toxins out.

For Corydoradine keepers who may not be aware, these fish excrete a slimy toxin when they are freaked. They are difficult to ship because of this and there can be mass die offs in tanks with heavy population of corys and similar fishes.

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I had JUST read something about that recently and was wondering how much of a problem it was. I think it said that some varieties of Cories produce more toxin than others. Is that correct?

As a defense mechanism, Corys excrete a toxin when they are frightened. In the wild, the purpose is to get a potential predator to spit them out. The toxins are quickly diluted by the stream/river flow. In an aquarium, the toxin sits. In tanks or bags with heavy cory population the toxin can build quickly and cause mass die-offs.

My guess is that one fish started getting stressed during the water change or just after for whatever reason. The others started noticing the presence of the first fish's toxins and started excreting their own, and a domino effect is started. It took some time for the toxin to reach a level high enough to negatively effect the fish.

This is a theory as to what happened, keep in mind. It never really hurts to put carbon in a tank. Another option is to do a massive water change just after one notices the stress in the corys (they have a limited supply of toxin that takes time to "restock") and treat with Melafix.

The slightly elevated ammonia and nitrate probably came from the dead fish in the tank for a few hours before you got home.

I'm not an expert on this by the way... I just sat through a couple talks by Ian Fuller and Erik Bodrock who discussed the issue.

Sterbai

chriscoli said:

I had JUST read something about that recently and was wondering how much of a problem it was. I think it said that some varieties of Cories produce more toxin than others. Is that correct?

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Sterbai are known for it, and Ian Fuller has shown a picture or video of a Sterbai poisponing itself while being bagged. I think he showed it at the Catfish Convention in October.

Blaise and I saw a Sterbai die at Mike Barber's house, after being bagged.

Other corydoras do it too.

I usually move my corydoras into a bucket before I bag them. I used to do it for convenience, but now I think it may help avoid the toxin problem.

I'm skeptical that this is the cause of the dieoffs here, although it's worth consideration. My understanding is that the toxin is only deadly in the immediate vicinity, as a mechanism for dealing with predators (otherwise, corydoras would kill themselves off, and thereby qualify for the Darwin award). I've never heard of an entire tank being poisoned. Like Holly, I wonder why a water change would cause this.

As far as nitrites and nitrates go, if the Eheim wasn't cleaned, why would there be a spike?

Water changes are inherently stressful, even if the eventual results are positive. The water chemistry and temperature changes immediately, to say nothing of the disruption of having vacuums, hands, hoses, sponges, etc. bumping around in the tank.

Andrew said:

As a defense mechanism, Corys excrete a toxin when they are frightened. In the wild, the purpose is to get a potential predator to spit them out. The toxins are quickly diluted by the stream/river flow. In an aquarium, the toxin sits. In tanks or bags with heavy cory population the toxin can build quickly and cause mass die-offs.

My guess is that one fish started getting stressed during the water change or just after for whatever reason. The others started noticing the presence of the first fish's toxins and started excreting their own, and a domino effect is started. It took some time for the toxin to reach a level high enough to negatively effect the fish.

This is a theory as to what happened, keep in mind. It never really hurts to put carbon in a tank. Another option is to do a massive water change just after one notices the stress in the corys (they have a limited supply of toxin that takes time to "restock") and treat with Melafix.

The slightly elevated ammonia and nitrate probably came from the dead fish in the tank for a few hours before you got home.

Click to expand...

That's interesting.

Sorry to hear about the losses, Blaise. I suppose that Andrew's theory is plausible.... no other reasonable explanation.

I remember hearing Bodrock talking about the poison as well. When I shipped a bunch of cories to Greg Steeves after his visit, I put all of them in a bucket of clean water... then I kicked the bucket a bunch, before I started bagging. This will supposedly, get them to sucrete any poison they have stored up.

I then bagged them in fresh dechlorinated water. Shipped about 25 of them - 5-6 per bag in 4" bags. Added nothing else but Ammolock and no losses with USPS Priority shipping to Texas...

mchambers said:

Sterbai are known for it, and Ian Fuller has shown a picture or video of a Sterbai poisponing itself while being bagged. I think he showed it at the Catfish Convention in October.

Blaise and I saw a Sterbai die at Mike Barber's house, after being bagged.

Other corydoras do it too.

I usually move my corydoras into a bucket before I bag them. I used to do it for convenience, but now I think it may help avoid the toxin problem.

Click to expand...

I just read something on this in the most recent issue of Amazonas. It is in the Jan/Feb 2013 issue. The article is by Ian Fuller and has a part in there about self-poisoning. I found it very interesting and it also lists the corydoras species most susceptible to the self poisoning. I am not sure if that is the cause in this case but found it very informative nonetheless.

Good Luck and hope the issue you are having is resolved soon without much more loss if any.



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Hadn't thought about the self-poisoning, though I did think about whether I might have introduced a poison of some sort. I've seen the cascade effect in bagged corys, and Eric Bodrock taught me some bagging tricks when I picked up some corydoras gossei at his house a few years back.

I'm treating with Melafix now, so I am not running carbon. Since I didn't test for nitrite, I'll run the bunch again tonight.

Blaise

Here's Ian Fuller's description of corydoras self-poisoning:

http://www.ianfuller.com/articles/authors/i_fuller/s_p_c/authors.html

Another item possibly of interest: I threw in a large chunk of polyfilter after the first water change. It turned an orange-red fairly quickly, which according to the packaging would indicate aluminum or iron. Not sure where the aluminum would come from, but the substrate does have laterite. However, I only do a shallow substrate vacuum, so as not to disturb the lateraite layer.

Blaise

Gossei and sterbai are among the most toxic species. That's why I always scare the crap out of my corys then switch them to clean water before bagging for auction.

Among the losses: c. panda, s. barbatus, c. atropersonatus, and c. loretoensis. Ancistrus must come from some real cesspools because they seem completely unaffected.

Blaise

don't know the reason but got the same problem,(i thought I wrote this) rinse sponge in fish tank water,use rain water for my tanks = death cories ???

Been there done that

Someone somewhere needs to collect and test said mucus for toxicity to confirm the reasoning involved in the conclusion that Corys can poison themselves. While it makes sense and Ian is definitely the Man, I'd like to see this confirmed in a lab and the name for the class of toxin. Not saying it's wrong, have lost Corys in transport myself, just a fan of "proof" that isn't solely deductive and it's the only way to prove that the observed mucous is the cause rather than a symptom/consequence of something else.

Assuming Ian, Eric, et al. are correct, as I'm inclined to, I'm still not buying a dozen fish poisoning themselves in a 30 gallon tank, especially as by now the stories of tanks of dead Corys at LFS would be legion where much greater numbers of Corys are routinely kept in much smaller tanks and subject to stresses far beyond what they typically encounter in homes. Then there's the fact that this was as you said "weekly" and presumably routine maintenance, and it's not adding up for me.

An observed five-degree drop in temp could have initially been much higher since the substrate, scaping and the tank itself are all heat sinks that would rapidly warm/cool any new water being introduced into the tank - that being said the INITIAL difference could have been as much as TWICE+ what you observed by the time you measured it (probably at the surface) which I'm guessing could be a pretty good shock to a small cold-blooded fish, and more so if the filter was shut off and the water in the tank wasn't mixing (cold water sinks).

In the last four years of doing water changes, aside from my involuntary predations on young Enantiopus, the ONLY other fish that I've EVER killed in this process are Corydoras. Armored they may be, but they are the most sensitive fish in my New World tanks and serve as my "canaries" when doing massive water changes on large tanks in that they respond negatively before anyone else if the resulting changes in water parameters caused by refilling are too swift and will simply go into a state of shock (much like what you observed/described). While I suppose this could also be a case of self-poisoning resulting from the previously referenced stress associated with having their habitat turned upside down, mine have NEVER manifest the symptoms (listlessness, disorientation, stupor, paralysis) or simply croaked from having 80% of the tank drained and/or everything in it removed - those symptoms ONLY occur at such time as the tank is being refilled.

In an evolutionary context, adaptive responses that frequently result in death (especially in the absence of any real threat) are poor survival traits as they severely limit/preclude an individual's ability to produce offspring that have the same genes/capacity to respond in kind. Natural selection is just rather unforgiving when to comes to suicide, involuntary or otherwise.

I don't believe your Corys went into shock and died from toxins they themselves secreted (would have to be from direct contact as there's too much water in the tank not to dilute the amount released). Much more likely in my mind that it was caused by too radical/sudden change in water parameters or temperature. Could well be wrong about this, but I do know I haven't lost a Corydoras (or Scleromystax) to water changes in two years+ since I began keeping an eye on incoming water temps (never warmer than the tank or more than 2-3° cooler), making sure that the incoming flow is evenly distributed throughout the tank, and pausing the refilling if it's 50% or more in terms of volume being replaced. Time was I used to "stun" mine pretty regularly and that hasn't happened in ages.

Do agree with Andrew about the observed water indices, and fins are aways the first/fastest thing to rot/get eaten on dead fish (they're only one/a few cell(s) thick). It's possible that some other rogue variable/contaminant was introduced into your tank during the water change perhaps courtesy of your municipal water supplier but the simplest explanation is usually correct and this one reads like operator error. I hate saying that nearly as much as you probably hate hearing it and wouldn't if I hadn't been (and likely will be again) similarly guilty of same on innumerable occasions - in any case, it's just my opinion and you now what they say about those...

The Polyfilter does not lie...

My money's on your municipal water treatment plant dumping a little something extra in the water.

Matt

dogofwar said:

The Polyfilter does not lie... My money's on your municipal water treatment plant dumping a little something extra in the water.

Click to expand...

And yet I did equal % changes on two other cory tanks that night, with no ill effects. And one of those tanks contains my sole surviving corydoras gracilis, which drop if you look at them askance.

After completing the big water change on the 30 last night, I did a change on a 10 with my C120s and 123s. These are all still fry, and no issues there.

I must admit, I'm as baffled as I am saddened.

Blaise