Julii Corys dying within days

[ProLoe]

Please share your wisdom!
We have a tank that's been running for 2 months, fully cycled for 6 weeks (14.5 gallons). We have 5 healthy and very active Blackskirt Tetras.

We added 3 Julii Corys on Wednesday (they were sold as Julii, but look more like Trilineatus to me). They arrived active and started to root around the floor (smooth gravel) and artificial plants, but over time they became more quiet and almost seemed to "shrink". Their skin was no longer iridiscent, their top fins were clamped. No spots or any other physical changes apart from what I described (I was careful to look at their barbels, but there was no sign of erosion from the gravel).

Yesterday the first one died, two more followed today, and the replacement fish the store gave us yesterday (which looked very healthy upon arrival) also looks very weak. When the first one died, we found him with a red spot on his belly the next morning (but he did not have that spot or anything else unusual on his belly the night before, he just looked thin and weak).

Through all this the Blackskirts are still looking great. We also checked the chemistry throughout and everything looks great (Nitrate 10, Nitrite 0, Hardness 200, Chlorine 0, Alkalinity 100, Ph 7.5, Ammonia 0) – no sign of ammonia spike when we added the new fish. Temperature is 75F.

At this point we’ve isolated the remaining Cory in a net cage within the main tank (can’t set up a quarantine that fast) - just in case there is something dangerous in the gravel or plants (even though both gravel and plants are specifically produced for aquariums and haven’t harmed our Blackskirts). We also did a 20% water change just in case (we do 15% every week and vacuum about half of the gravel each time).

Any suggestions on what may have happened to those poor Corys? Obviously we’re not going to add any more at this point, but it would be good to know if there is anything we can change to make it safe for them in the future.

BTW the Blackskirts did not seem to bother them much, but they kept stealing the bottomfeeder tablets that we put out for the Corys. – Nonetheless there was still a bit of loose food on the floor - and the Corys could not die of hunger within a few day or could they? The quarantined one has been eating a lot since we put him in the net cage.

Thanks so much in advance!

[pleconut]

Seems from what you've wrote here, there's not a problem with your tank that would have caused this, although I'd possibly rethink on the gravel, but again you stated this didn't seem to cause a problem for them. Were they all from the same source it could have been there was a problem with them already. Another question I'll put back out there on the forum are these one of those cories that release toxins, could it have been this that was possibly a cause.

[ProLoe]

OMG, that self-poisoning could definitely play a role. Will do a much larger water change ASAP.
Also, is it possible that oxygen levels in the bottom of the tank are too low for them because there are bacteria sitting in the gravel.
Higher levels of the tank would be less affected explaining why those tetras are just fine ...
Does that sound plausible?

[pleconut]

Have you checked if these particular species of cory can actually self poison, it was a thought but not something I know for certain can happen to this particular species, I was hoping someone else can confirm it or not. Oxygen levels may play a role, but if there's adequate surface agitation, dissovled oxygen probably wouldn't be the cause of the deaths, another way to guage an idea with cories that disolved oxygen levels is a problem, is if they shoot up for gulps of air very frequently. In terms of bacteria in the substrate unless its not sufficiently cleaned regularly enough, it can cause infection in barbels and sometimes, I think, a sore belly area. I think its unlikely that all the nearly all ones you got would die because of something untoward happening with your tank.

[bekateen]

Although I wouldn't describe trilineatus as a "robust" species in terms of its ability to tolerate poor or stressful conditions, I believe it is not prone to self poison as are other species, like

Corydoras sterbai

. But that's my experience; others may have different experiences with trilineatus. (edit: I stand mistaken; I've since been told that trilineatus are very vulnerable to self-poisoning. I guess I've just been lucky with no trilineatus deaths.)

Good luck, Eric

[dw1305]

Hi all,

Also, is it possible that oxygen levels in the bottom of the tank are too low for them because there are bacteria sitting in the gravel.
Higher levels of the tank would be less affected explaining why those tetras are just fine ...
Does that sound plausible?

Yes it does sound plausible. I'm sorry for your losses, and you may never know what caused them, but my suspicion is that a lot of "unexplained" deaths are due to water quality issues, and the water quality issue that causes death most often is low levels of dissolved oxygen. If you could tell us what type of filtration you have that might help, some forms of filtration are much more efficient at biological filtration, and low levels of oxygen often lead to problems with biological filtration.

We have a tank that's been running for 2 months, fully cycled for 6 weeks.......(smooth gravel) and artificial plants........We also checked the chemistry throughout and everything looks great (Nitrate 10, Nitrite 0, Hardness 200, Chlorine 0, Alkalinity 100, Ph 7.5, Ammonia 0)

Not every-one will agree with me, but all of those things set alarm bells ringing for me. I'm a great believer in an establishment period for tanks, having a sand substrate, having plants, and I'm not a great believer in the accuracy of test kits.

Have a look at <http://www.planetcatfish.com/forum/view ... =4&t=41038>.

cheers Darrel

[rmc]

Just as a note, before I purchased my WC C.trilineatus from a reliable source (Jeff Michels of aquaticclarity.com) I attempted to purchase LFS "C.julii" which were indeed C.trilineatus 2 times. Both occasions the entire groups ended up dying within a few weeks. Their behavior before dying was quite unusual and I saw "whirling" that I have seen with associated with sick or dying tetras before, but never Corydoras. When I approached my LFS guy about where they came from he told me that all the "C.julii" they get in are farm-raised in SE Asia. I have purchased and kept 1000's of WC and TR Corydoras, and I've never had any other ones die like this. Once I got my WC group of 6, I found them very easy to keep and hardly a "demanding" species, I had them for 2 years, and did not experience a single loss, even the fry were pretty hardy once they passed the 1 month mark.
One a side note, unless I have been living under a rock and have missed something how would it be possible for 3 Corydoras to release enough toxin to pollute a 15 gallon tank? And on top of that wouldn't that water be so toxic that the tetra's would also die? I think there's some confusion going on here. The toxins released by Corydoras under stress, in my experience, is only potent in an extremely small body of water like a bag or specimen container. I think if this toxin was potent enough to pollute(to the point of causing death) even a 5 gallon tank most aquarists would find this genus almost impossible to keep alive in captivity. If I'm wrong on this please feel free to provide evidence that points in that direction.

[bekateen]

One a side note, unless I have been living under a rock and have missed something how would it be possible for 3 Corydoras to release enough toxin to pollute a 15 gallon tank? And on top of that wouldn't that water be so toxic that the tetra's would also die? I think there's some confusion going on here. The toxins released by Corydoras under stress, in my experience, is only potent in an extremely small body of water like a bag or specimen container. I think if this toxin was potent enough to pollute(to the point of causing death) even a 5 gallon tank most aquarists would find this genus almost impossible to keep alive in captivity. If I'm wrong on this please feel free to provide evidence that points in that direction.

I've never personally experienced self-poisoning corys (or any other fish for that matter), but I've read about the phenomenon on this website. I think you're right that a full-sized aquarium should not allow the "self-poisoning toxin" to build up sufficiently. To be fair, I've never read about what that toxin actually is, but obviously something kills those fish.

Regarding your experience with trilineatus, my experience with TR fish is the opposite of yours. I've had five trilineatus that I bought from a few different stores, including PetSmart and I think Petco, both of which are notorious for low-quality fish. I guess I was fortunate in that my adults have done very well; no weirdness over several years. Perhaps the health of the stock of TR fish is a bit hit-and-miss.

Cheers, Eric

[TwoTankAmin]

Stress toxins. Under stressful conditions (such as being chased with a net and bagged) some Corydoras species emit a toxin from glands at the base of their gill covers, an effective defense mechanism when a predator is bearing down. In the confines of a shipping bag, Cories can poison themselves, Ian Fuller notes in the January/February 2013 issue of Amazonas.

from http://www.skepticalaquarist.com/corydoras-genus

This article is available in full on Ian's site to all paid members (I am not one) http://www.corydorasworld.com/articles/?p=43

Here is a brief summary from that article I located:

All species in the genus exude a white milky substance from below the gill area, possibly connected to the pectoral spine. This substance is extremely toxic to all fish, and kills within minutes. The release of the substance is triggered by severe stress, such as often occurs during netting and capture. Mr. Fuller includes a photograph in the article of this substance on a C. sterbai, and he notes that it is the only existing record as far as he is aware. In the confines of a bag of water, the substance kills the cory quickly. Small bubbles will appear at the water surface, and if the cory is taken out of the bag of water immediately and placed in fresh water, it may recover.

Mr. Fuller presents the view that this is likely a defense strategy on the part of the cory; if the fish is caught be another fish or bird, the automatic release of this toxin could result in the predator releasing the cory. The release of the substance is probably triggered by stress, and not controlled; thus, the cory releases it in the bag, even though its own imminent death will follow.

Mr. Fuller suggests that the frantic chasing of the cory around the tank during capture might cause the fish to release the toxin in the tank, rather than the bag. He also recommends taking home a second bag of the tank water, taken out prior to any capture attempts, in case the fish needs to be transferred en route. Once the toxin is released--and unless one actually sees the release when it occurs this will be un-noticed--the only remedy to save the fish is an immediate 100% water change of the container.

from http://www.tropicalfishkeeping.com/catf ... th-126966/

[bekateen]

Thanks TTA for the extra info. I am a member of corydorasworld; now that I am aware of this, and as a person who studies the chemistry of skin secretions for my profession, I feel the need to read this article and investigate further. If we can recreate the conditions of stress (without killing the fish), we can probably harvest some of this stuff and analyze it with HPLC and mass spec.

Cheers, Eric

[rmc]

Really interested in the results if you can do that Eric, that would be super cool!!! C.sterbai - classic toxin producing Cory. Spook them in a small container and see if they lay on their side and produce a little toxin.

[bekateen]

Hi Rob, Yes we can do it soon. Our dept is getting a new high-tech toy, a combination HPLC/MS system (Thermo Scientific Orbitrap Fusion, if that means anything to you). It's not installed yet, but should be by the end of the school year. How big does a sterbai need to be to produce a collectable amount of this toxin? Any idea?