Curved spine, sunken belly disease – esp. livebearers

Curved spine, sunken belly disease – esp. livebearers

  • Author aylad
  • Creation date
A lot of people seem to be seeing a particular set of symptoms in their fish – most often livebearing fish like platies, mollies, and guppies. I’ve got a lot more experience with these symptoms than I’d like, so I thought I should type up what I know about it. Additionally, I hate having to tell people that euthanasia may be in order... so I'm saying it once, here.

In brief:


The key symptom is curved spine – the fish looks hunchbacked – and this usually shows up with a caved-in belly, as though the fish is starving to death. Other symptoms are listed below under “comments.”


First and most important, THE FISH MUST BE REMOVED FROM THE TANK. Immediately. NOW.

Put the fish into quarantine if you have a quarantine tank available. If you don’t have a QT set up, see the “quick and dirty QT” instructions below.

If you can’t (or won’t) set up a QT, euthanasia is the second-best alternative. I do not make this recommendation lightly, but if the disease is allowed to spread to other fish, you’ll lose a lot more than this one. Trust me: I lost an entire tank. One sick fish can kill dozens.

As far as treating the fish once it’s in QT, I don’t know a medicine that works. I’ve tried Prazipro, Tetra Parasite Guard, fenbendazole, and a malachite green/formaline combo (Quick Cure). None worked. Try something else, and let me know how it goes. If it fails, let me know so that I can add it to the list; if it works, let me know so I can share the information here.



Check the fish for worms protruding from its anus. If you see worms, it might be camallanus worms. There is a stickied thread on CW here. If you don’t see the worms, then I have no idea what it really is. The general symptoms match parasitic infection, but as mentioned under “Treatment,” I’ve tried a range of antiparasitics without success.

Some have suggested that these are symptoms of fish TB. I don’t think that’s what my fish have had, so I would hesitate before assuming that TB is in your tank.

Others think that it’s a result of inbreeding or deformity. The fish may be more susceptible to it due to inbreeding, but I can verify that it is a communicable disease – not a congenital defect.


The only thing I’ve found that works is aggressively removing fish as soon as they show any symptoms at all. Keep a QT setup ready to go. If you notice a fish’s back curving oddly or its stomach flattening out, remove it immediately. QT is important because you can isolate the fish even before you’re “sure” that it’s sick; you probably will wait longer before euthanizing, and that gives other fish more chances to catch it.

Platies seem to be the most common victims of this disease, so I recommend quarantining all platies and other livebearers for a minimum of 2 full months before introducing them to your tanks. All new fish need to be quarantined for a month anyway, but I’d extend that for livebearers. The disease takes a long time to manifest, so extra time is needed.


I can’t set up a QT and/or my QT is full, but I can’t kill my fish. What are my other options?

You can watch your other fish catch the disease and die. Look, I know exactly how you feel, because I was in exactly this situation for a long time. At a guess, I’d say I watched 2 dozen fish die because I failed to take action sooner.

How can I humanely euthanize my fish?

There’s a very thoughtful thread
here covering that topic. Use your best judgment to find a method that works for you.

You talk about platies being sick. Can other fish catch this?

Yes. I’ve seen neons and mollies die of these symptoms after being exposed to infected platies.

Are the symptoms the same for all fish?

Well, yes and no. The mollies that died were less obviously sick than the platies, probably due to their larger body size hiding the curved spine and sunken belly. In general, though, their behavior seemed very similar.

Should I sterilize my tanks after this illness?

Other people will tell you that you should. I have no opinion. If your fish have what mine had (which is not guaranteed), I don’t think it’s necessary. On the other hand, better safe than sorry. It’s your call.


When I first posted on FishLore about these symptoms, I had not seen anyone else describing this disease. (Maybe I just hadn’t noticed.) Only one of the people who responded to my thread mentioned having seen the same symptoms. I think that at that time it must have been rare. Now, it seems that I see at least one thread about this disease every week… always livebearers and usually platies. I have begun to believe that it’s an epidemic.

Many times, the fish hangs out at the bottom of the tank and doesn’t come up except for food; it may have trouble eating. Many people report that the fish spits food back out instead of swallowing normally.

General signs of fish illness (clamped fins, weakness, loss of color, etc.) may also appear.

The disease takes a long time to show up. Infected fish may not show symptoms for over a month after exposure. Keep an eye on your fish for at least 2 months before adding new fish to the tank.

The reason that I don’t believe it’s fish TB is because fish TB should persist in infected tanks even after the fish are gone, but it seems that I only ever see the disease spread directly from fish to fish. Fish placed in formerly-infected tanks – even tanks with old water and filter media – have remained healthy. NOTE: This has been my experience. Your mileage may vary.

Quick and Dirty QT

This setup is to be used in emergencies only. It’s tiny and otherwise inferior to a good 10-gallon QT/hospital tank with an established filter. There are some great instructions for a more permanent QT setup here. This should only be used when your real QT is occupied.

You need a food storage container from the dollar store (the larger the better) and a cheap air-powered corner filter from your LFS or Obviously you need an air pump as well, but for this size “tank” a super-tiny one will do. If you can buy everything locally, the whole setup might cost $5-10. If you’re willing to spend a bit more money, buy a small heater to toss in there.

I suppose I should say that a heater is necessary, but it depends on your ambient room temperature and how long you’re able to keep your fish alive in this condition. It would be more humane to provide one, though. If you find a cure that works, let me know and I might buy you a small heater as a thank-you. (No promises.)

When your fish shows the symptoms listed above, pull out enough tank water to fill the container, scoop out enough gravel to fill the corner filter media box, and set everything up. The gravel should have enough beneficial bacteria for one or two small fish, particularly if you only feed a tiny bit. When you’re done, toss out the gravel – don’t put it back into your main tank, just in case.

Keep in mind that a full-size 10-gallon QT with a real filter and a heater should only cost about $40 anyway, plus some sturdy furniture to put it on if you’re not willing to set it on the floor, so that would be a better alternative at a reasonable price.


I’ll update this post as more information becomes available. Please let me know if there’s a question or if you have some advice to add.

If you have fish with these symptoms and have clear photos showing the spine/belly deformity, I'd like to use your photos. Please let me know if you're okay with me adding your photos to this post. Thanks in advance!


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  • NeuronB
  • 5.00 star(s)
I was searching all over the net for this and finally found it here. This issue seems exclusive to livebearers specially platies. My three platies died in a row. Fourth one is due to die soon. I have had other fishes like Zebra Danios and Widow Tetras and this doesn't seem to affect them at all. I have made a promise to never buy platies.
Very informative and to the point
Same thing happened to my fish. I posted some pictures and I'll PM you them. I unfortunately don't have the later stage when her stomach was sunk in. No meds solved it, she just got ill over 3 weeks and showed no bad symptoms other then clamped fins. Then she started to sit at the bottom of the tank more, only came up for food, arched back, and finally a sunken stomach. I removed her and should of ahead of time. Hopefully it doesn't spread but I'll deal with it sooner next time.
  • teko116
  • 5.00 star(s)
I never knew about this, sounds awful. Have you gone to your LFS to see if fish are exhibiting these symptoms? I may have seen some at my LFS nearby...
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