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"When all appears sunny and Buddha smiles, it is axiomatic that one begins edging toward the fire escape." -- S.J. Perelman

I really thought my problems were over. After 18 years, I had finally found the solution to the epidemic of seemingly unstoppable bacterial infections that had repeatedly wiped out the fish that I take care of in the local library's 50-gallon tank -- just keep an army of bottom-feeders in there to eat all the food the moment it hits the bottom, so the other fish won't nibble it off the bottom later when it's half-decayed and give themselves massive food poisoning. I was able to reliably keep beautiful and delicate fish, such as Blue Emperor Tetras and Three-Striped Pencilfish, alive and healthy.

Then, 3 weeks ago, one of the Blue Emps came down with probable Neon Tetra Disease. And I followed the advice of a clerk at my LFS who was extremely knowledgeable and whose advice had never led me astray in a decade: you can safely keep that dreaded disease from spreading to your other fish by using a 50-50 mix of Nalidixic Acid and Neomycin. Years before I had once tried to use Nalidixic Acid alone, in exactly the dosage recommended on the package, and wiped out an entire aquariumful of fish -- but Ryan assured me that if you use only half the package-recommended dose of Nalidixic, and substitute harmless Neomycin for the rest, there is no danger.

So I followed his advice. And it immediately wiped out 36 of my most beautiful and hard-to-replace fish: about $140 worth, by my count. Even in a half-diluted dose, when I used Nalidixic I might as well have poured cyanide into the tank. It especially goes after Cyprinids, including the ordinarily tough little Barbs -- but it killed virtually everything in the tank except for some of my Characins. Over the last 3 weeks -- despite repeated frantic massive water changes to dilute the stuff -- it has killed all my Lamb Chop Rasboras, all my Odessa Barbs, all but one of my Brilliant Rasboras, all my multiple types of Loaches (including my $15 Angelicus Loach), all my Corydoras catfish, all but one of my Diamond Tetras, all but two of my Beckford's Pencilfish, both of my Three-Striped Pencilfish (beautiful, and very hard to replace despite their low cost), and about half of my Blue Emperor Tetras. Some of the Blue Emps, thank God, have held on -- and the relatively small number of Cardinal, Glowlight and Cochu's Blue Tetras in the tank seem to be surviving the stuff OK -- but I feel like I'm running an Auschwitz for fish. I have no idea how long it will take me to replace this collection.

I have no Cichlids, Anabantids, Livebearers or Rainbowfish in the tank, and so can't judge the deadliness of Nalidixic on them. But I can tell you all, with no qualifications: AVOID NALIDIXIC ACID LIKE THE PLAGUE! It is the ONLY fish medicine I have ever encountered, of any type, that does any detectable harm to fish -- but it is absolutely DEADLY.

Now I have to go home and break down in sobs again...

Sorry to hear about your tank, Bruce.

If I am remembering my molecular biology correctly (and I should, as I used the stuff last year in laboratory while doing bacterial antibiotic resistance stuides), nalidixic acid prevents the action of the enzyme DNA gyrase (which reduces helix strain on DNA supercoils). It is a broad-spectrum antibiotic that is used in humans widely because humans don't have DNA gyrase, and I didn't think fish (or any eukaryotes, for that matter) possessed it either. Someone else may correct me on that, but I'm almost positive on it.

One thing that it will absolutely do (and probably did in yout tank) is nuke your biological filter. All the water changes that you've been doing has probably helped remove a lot of the organic debris that has accumulated (especially with all the dead fish), but if you haven't already I'd start running carbon on that tank PDQ.

After consulting the MSDS for NA, it specifically gives the warning that it is very toxic to aquatic animals, although it doesn't give a reason why. As such, I can't imagine why it was being recommended as a fish treatment (although I've heard of it being used before, just not with such tragic results).

Again, sorry for your loss.

Joe Potato

Thanks for both the sympathy and the advice. "Very toxic to aquatic animals", eh? And neither of the manufacturers I bought it from issued a whisper of a warning -- except that one of them does say that you should carry out a 1/3 water change "before using it a second time". I never got the chance to get that far...

Ryan professes bafflement, saying that he's used the 50/50 Nalidixic/Neomycin mixture repeatedly in store tanks with no problem. I wonder whether it's possible that SOME of my problem did come from the stuff zapping my beneficial bacteria and allowing ammonia and nitrites to build up in the tank. But I can't see how that could be all the problem -- especially given its varying deadliness among different species; it killed all my "Lamb Chop" (Espei) Rasboras almost immediately, but the other fatalities took longer. And I HAVE done a pH test -- which showed pH at 6.5, just where I wanted it.

Anyway, thanks again for the info, and I will have the store do ammonia and nitrite tests on a water sample Monday. I've already changed the carbon filter twice over the course of this disaster; it may be advisable for me to also add some Cycle to the water to reestablish the biofilter bacteria. I do hope that this is the very last of my 18-year string of Disastrous Learning Experiences where tropical fish are concerned...

My condolences to, I just wanted to say hang in there.

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My Tanks at Photobucket

And neither of the manufacturers I bought it from issued a whisper of a warning -- except that one of them does say that you should carry out a 1/3 water change "before using it a second time". I never got the chance to get that far...

I found one manufacturer that said to do the 1/3 water change within 24 hours after dosing. http://www.aqualifesupport.com/getDetail.php?ID=363292 *wonders why none of the rest of them come with this warning.

And with a lot of digging I found this:

These antibiotics have been shown to damage the nervous system of other animals and none are approved by the FDA for use with fish.

at this site http://edis.ifas.ufl.edu/FA084 (not that you are going to eat them but it does look like it can do nasty stuff)
Not that all of this will help your situation, but it may be another clue as to what happened. I'm sorry for your losses, it's heartbreaking.

---

I used to be Snow White, but I drifted.
~ Mae West

(Heavy sigh) Thanks, again, for the help, even if we all discovered this too late. (The Web descriptions of possible harmful side effects of Nalidixic on humans are bloodcurdling -- cancer is only one of them. My mother, who has a conspiratorial turn of mind, suspects that -- after the FDA banned this stuff for use on humans -- the drug companies decided to dump their remaining supply on the animal market, and specifically the aquarium market. I wouldn't be surprised to learn that she's right on this one.)

My death count is now up to 38 -- I lost two more Blue Emps over the weekend. After still another water change, I had also put in four Corydoras catfish on Saturday, because -- with no bottom-feeders at all -- the surviving fish were starting to nibble on partially-decayed food on the bottom again. I can't tell whether more than one of the Corys is still alive, because at the moment the water is so cloudy -- thanks to an apparently harmless bacterial bloom -- that I can barely see any of the fish; it's even possible that there are more corpses in there, although I did a lot of digging around and couldn't stir any up. On top of that, the filter pump impeller had gotten stuck due to debris some time after Saturday afternoon, and God knows what additional harm that did. (Oh, and I HAVE just put in some Cycle to try to restart my beneficial bacteria. Thanks particularly to Joe for that tip.)

Latest report: as of today, I haven't lost any more fish -- including any of my four new Corys, who are busily going about their janitorial task. Also:

(1) The extremely cloudy bacterial bloom is fading.

(2) I've dumped two full doses of Cycle into the tank.

(3) A test of pH, ammonia, nitrites and nitrates by the LFS shows them all perfectly in the middle of the green range. This confirms my belief that it was the Nalidixic itself -- instead of its destruction of my biological filtration -- that was deadly to the fish.

In short, we now appear to be in the post-disaster phase (assuming I don't lose any more Blue Emps; I'm now down to 4). I will nevertheless wait a long time before issuing the All Clear and starting to (expensively) restock the tank. Grrrr.

Glad that you finally have the situation under control. I also have a major panic of Neon Tetra Disease with one of my Congo Tetra 2 months ago. I did some research and all sources said it is incurable and highly contiguous. I promptly removed the Congo and destroyed her humanely. Then I did a thorough vacuuming of the gravel. All fishes have been doing fine since then. I was really lucky.

Good luck with your re-stocking.

I'm glad to hear that things have turned around. Hopefully you won't loose any more fish to any unknown long term effects.

---

I used to be Snow White, but I drifted.
~ Mae West

If I ever run into Neon Tetra Disease again, I'll euthanize the symptomatic fish and then add Neomycin, Quinine, and maybe Nitrofurazolidine -- all of which I've used in the past without poisoning any fish (although Nitrofurazolidine is forbidden for human use because of possible carcinogenic effects). With luck, any one of those compounds may kill some of the free-swimming organisms -- and in any case, the disease seems to be spread much more by infected fish dying and having their corpses eaten.

Just to let you know, its not all doom and gloom with NTD of the origiinal 10 i boughtabout a year and a half ago, knowingly affected as an experiment, the combination of anti malarials, blackwater extract and protozin worked. Four out of the 10 survived, and appear to be completely healthy.

Now its just getting the lil buggers to breed, and pass the resistance on.

Wishing you some better luck there bruce, it sounds like a heartbreaker, my heatfelt sympathies, I know how hard you work to do the very best for your fish.

Thanks VERY much for that advice. I already use Blackwater tonic regularly (I've heard it described as a near-necessity to keep Blue Emperors from coming down with bacterial infections). Which "anti-malarials" did you use -- quinine, or something else?

No more deaths yet -- except that one of my two remaining Cochu's Blue Tetras, who up to then had been acting completely polite for months, suddenly went on a vicious vendetta against the other one and finally made him jump clean out of the tank overnight! These are weird little fish -- I suppose he decided, in that tiny little mind of his, that the other Cochu's Blue had Dissed him in some way. Now he's back to acting polite again...

One additional note: another clerk at the LFS whom I talked to today already took a much dimmer view of Nalidixic Acid than Ryan. He had tried it on a combined tank of Characins and Angelfish -- and while the Characins (I can't remember the species) survived OK, the Angelfish immediately started swimming upside down and then died massively.

This seems both to indicate that Nalidixic is also deadly to Cichlids (something I wasn't sure about), and that it does indeed attack fishes' nervous systems. Characins, so far, are the only family of fish I've encountered that can survive the stuff at all, and they aren't very good at it.