My tetra is exploding with worms and I don’t know what to do

  • #1
I have five cardinal tetras in a well established five gallon tank and two of them currently have what appears to be long white worms. The worms first appeared about a month and a half ago when one of the two had a small whitish spot on his side, but it didn’t seem to change and didn’t look like any disease I knew of so I brushed it off as an imperfection with its scale or something. However, after a while I realized that they were actually little worm things, which left me absolutely horrified. I had gotten these two fish about two months ago and I believe they must have come with the worms, as my water quality tests out fine and the three other cardinals, which I have had for a long time, are all fine. I started dosing them with metroplex, and believed it to be working after one of the worms in the gills of one of them disappeared. However, after a two weeks of stagnation, one of the poor little guys suddenly looked like he was about to explode. He has four or five worms that I can see, and the worms appear to be coming to the surface, causing the scales around them to puff out and look like a callus or blister about to pop. One of the largest worms actually has a couple millimeters of the worm sticking out of the side of the fish. This is happening as well on the other fish, although that fish only has one small worm on its side.

Normally I would be thinking of euthanizing a fish that looks this bad, especially since I can’t quarantine, but they are both acting like nothing is wrong. Their color is great, they eat and move as good as usual, they stay with the others and don’t hide on their own. I’ve tried and been unsuccessful at looking online to see if I could get an identification on what kind of worms these are. Has anybody had this happen before and is there a different treatment I should be trying? What are their chances of survival?


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  • #2
This is really interesting. I’m curious to see what others have to say. I’ve never heard of or seen anything like this. It kind of reminds me of dracunculiasis but it’s been nearly eradicated from Earth and while fish can carry the worms, they only pop out in mammals so there’s no way it’s that. But keep us updated… I’m really curious on what this is

Also some questions: How long have you had the fish? And do you feed live food?

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  • #3
I’ve had the fish since about the end of July/beginning of August. The white blemish that ended up being a worm on the one showed up pretty early on, so this has been progressing for probably at least two months. The two of them came to me in two batches, but they were both from the same shipment to the fish store. Of the two I originally bought, one of them had a little bubble/blister looking thing right by his eye, which I posted about on this forum. I ended up taking him back to the store and exchanging him for another cardinal, one of the ones I have today. I don’t if that blister thing on the one I returned could be at all related to the worms that his shipmentmates have, or if it’s totally separate. I’ll attach a picture of him as well in case it sheds any light on the issue.

No, I don’t feed them live foods and haven’t ever. I don’t think there has been anything I’ve introduced to the tank that would have infected these guys with worms.


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  • #4
More pics... The worms are becoming more and more prominent and there is a tiny one under the fish’s eye as well.

And thanks to whoever changed the location of this thread to the one for sick fish. I’m terrible at trying to navigate this place.


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  • #5
Hopefully someone replies soon who might know what’s going on.
Poor fishies.
  • #6
Interesting situation... metroplex is metronidazole which we use to deworm dogs and cats and probably should have worked on these worms as well.. did you follow the instructions exactly as the bottle recommended? I’m thinking if you added it to the water, maybe this time you should try mixing it in the food so the fish eat it.


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  • #7
I’ve been using the metroplex in the water because I have so few fish that I would be feeding it to that I would be throwing the majority of the medicated food away, which hurts my heart cause I’m a penny pincher. I’ve had success curing fish with other parasites by dosing the metroplex in the water before, but I guess tommorow I’ll mix it up and feed it to them with their food since it’s not working so far. I’ve got some focus too so that will help.
  • #8
These aren't worms but Dermosporidia to which Cardinals are quite prone.

It is in fact quite harmless amd mainly an esthetic issue. It isn't lethal and to me there is no treatment / cure.
  • Thread Starter
  • #9
Thanks! Looking at pictures I’m sure that’s it.

If what I’m reading is true, then this is a fungus and not actually a worm. In that case, I assume something like kanaplex would be better for treatment. I know looking online that people don’t seem to have a consensus about wether or not this is treatable (some say no, others suggest ridiculously expensive dewormers, which makes not sense if this isn’t a worm). What do you think the likelihood is of this passing to my other cardinals? They are all very healthy and have made it through countless other diseases and rookie mistakes that killed off some of my weaker cardinals (I have one that is two years old and is one of my first fish, I am very attached to him). I don’t want to kill the two infected ones if the disease isn’t a death sentence for them just to spare my other three, but I might have to. Do you think the kanaplex might have any validity as a treatment?

I’ll call the fish store today and see if they know the fate of the one I returned (they had taken him back to quarantine and treat him) or if they know if any of the other cardinals from that batch have the same problem I am having.
  • #10
Personally I would not treat healthy fish with any hard med. kanaplex is hard on the fish. You’ll lower their immune systems and make them more prone to secondary diseases that will harm them


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  • #11
While I was writing this one of the little wormy not-worms one the side of my worse infected fish fell off. It was the one that had been sticking out the side of the fish. I saw it floating in the water and pulled it out with a net. The fish looks fine where the stuff came out.

Ill do a water change today and put the carbon back to get rid of all the metroplex clouding up the water. For the time being I guess I’ll just make sure my water quality is pristine and hope it clears up on it’s own.

Thanks for the help. I’ll post again if anything changes.
  • #12
I've never witnessed a succesful treatment as.long as.I am on forums.

I think, as with a lot of issues, the immunesystem of the fish is the keyword., clean water, no stress etc.....

I suspect the LFS euthanised it in seconds to be honest. Keeping and treating one single Cardinal ??????
But.maybe I should have more faith in people.
  • Thread Starter
  • #13
Unfortunately this morning I woke up to my worst infected fish dead He was floating upside down at the top of the tank. I’m a little surprised because as far as I could tell he was doing very well. Three of the four spots of infection had come off and he only had the one underneath his eye still intact, and it appeared that the other spots were healing up nicely. Color and appetite still good. My only concern had been that my oldest fish had started bullying him a bit.

Now I’m just hoping that the other fish makes it. The spot of infection came off a couple days ago and he is acting like a completely normal fish, with no other infection spots showing thus far.
  • #14
Sorry to hear!

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