Guppies With Bent Spines – The Causes And Preventions!

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It is extremely common for guppies to suffer from bent spines. The most common cause of a bent spine in guppies is a condition known as Scoliosis. When a fish develops Scoliosis, the spine becomes bent into a ‘C’ or ‘S’ shape. Unfortunately, there is no known cure for Scoliosis and euthanasia is often the ultimate outcome.

It is easy to see why guppies are one of the most popular freshwater fish in the hobby. Their bright colors, easy-going nature, and simplicity to breed have cemented their popularity forever. I first started keeping guppies over 30 years ago when I was given a 10-gallon tank with a small group of guppies. I don’t think there has been a single day from then to today when I didn’t have at least one tank full of guppies in my fish room.

Anyone who has kept guppies for more than 5 minutes will non doubt have come across at least one guppy with a bent spine. Unfortunately, bent spines in guppies are very common.

Scoliosis (Bent Spine)

Scoliosis is a condition where the guppy’s spine becomes bent into either a ‘C’ or ‘S’ shape. Scoliosis most commonly develops during the larval stage of growth before the guppies are born, but it can also develop after birth.

Scoliosis can also develop in adult females and is often caused due to their tendency to be constantly pregnant. In the wild guppies would naturally have seasons when they breed and seasons when they don’t. In our aquariums we rarely allow the water temperature to fluctuate, giving the fish the impression of ‘seasons’.

Inbreeding is another major cause of bent spines in guppies. In the enclosed environments that are our aquariums, guppy parents will inevitably breed with their own offspring, and potentially with those offspring too.

In just a couple of years, you can have multiple generations of guppies interbreeding with each other. This lack of new genetic material can cause birth defects in your guppies.

Scoliosis does appear to be a condition that is easily passed down from parents to fry. Whenever a female with a bent spine is allowed to breed, there will always be an increase in the offspring having bent spines too.

Other Causes Of Scoliosis

Other causes of Scoliosis in guppies include;

  • Overcrowding
  • Low levels of oxygen in the water
  • Poor diet
  • Poor water quality


Overcrowding can happen so easily in a guppy tank. Happy, healthy guppies multiply at an amazing rate. Before you know it, the 5 guppies you purchased from the pet store 6 months ago are now 80 fish, putting additional pressure on your filter.

As the number of fish in an aquarium increases, it can be very easy to under or overfeed the fish. Underfeeding and overfeeding both take a toll on your guppies.

When keeping livebearers, it is always good to have a plan of what you will do with the additional fish. You might be able to sell the surplus to your local store or other fish keepers. Maybe you keep your guppies with a slightly larger fish, like an Angelfish or some Gouramis that will eat some of the babies, keeping the numbers in check.

Low levels of oxygen in the water

Aquariums can end up with low oxygen levels if there are too many fish or if the water quality drops. The first sign of low oxygen levels will often be fish ‘gasping’ at the surface.

To prevent or cure low oxygen levels, consider adding an airstone to the aquarium, or maybe adjust your filter output so the water leaving the filter agitates the water surface more.

Poor Diet

Guppies need to eat good quality food to ensure they receive all the nutrients required to remain healthy. When we feed them a poor diet, they quickly suffer. I have had tremendous success feeding my guppies Bug Bites from Fluval which I just order from Amazon (check the current price HERE).

Other additions to their diet that will be appreciated include frozen or live bloodworms, daphnia, or brine shrimp.

Poor Water Quality

Poor water quality probably kills more guppies than any other factor. Poor water can include high levels of ammonia, nitrite, or nitrate, low levels of oxygen, too high or too low pH, or even just an excess of dirt and detritus floating around in the water column.

Frequent, large water changes are often the best solution to poor water quality.

Fish Tuberculosis

Fish Tuberculosis can also lead to bent spines in guppies. I have written more about Fish Tuberculosis is this article HERE.

What To Do If You Have To Euthanize A Sick Fish?

Although guppies may be able to live a fairly normal life, even with a very bent spine, there may come a time when perhaps your guppy stops eating, or another fish constantly picks on it, and you decide the kindest thing to do is euthanize the guppy.

There are lots of ways you SHOULDN’T euthanize a sick guppy. Please do not put them in the freezer or drop them in boiling water. Never try to suffocate them or use carbon dioxide to kill them.

The currently accepted humane way to euthanize a guppy is it follow this procedure;

  • Place the guppy in a small container of tank water.
  • Slowly add drops of clove oil to the container
  • Once the concentration becomes high enough you guppy will lose consciousness
  • After around 10 minutes Hypoxia (deprivation of oxygen) will set in and your guppy will pass away.

I recently wrote an article titled How to Euthanize A Sick Guppy? which gives step-by-step instructions and includes a video.

In Conclusion

Bent spines in guppies are very common. There are lots we can do to help prevent it from happening in the first place, but not so much once the spine is bent. Make sure you keep your guppies in an aquarium with ideal water parameters, feed them a quality diet, and try to keep overcrowding and other stress factors to a minimum.

A bent spine doesn’t automatically mean a death sentence for your guppy, but it does mean you may have to take extra care of it, making sure it gets enough food and isn’t being picked on by other fish.

Try to ensure any guppies you have with bent spines aren’t allowed to breed with the other fish, otherwise, you will just end up with several generations of fish, all of which have poor genetics.

About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James

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