6 Reasons Your Guppy Has a Bent Spine

Do you have a guppy with a bent spine or other spinal deformity?

It’s a relatively common deformity in guppies, especially female guppies.

The cause of this deformity in guppies is usually scoliosis – a curvature of the spine. Fortunately, scoliosis in guppies does not often impact their quality of life.

On the bad side, scoliosis is an untreatable condition in guppies, so the only option is euthanasia on the rare occasion it does impact your guppy’s quality of life.

Anyway, this article will cover the causes of a bent spine (scoliosis) in guppies and some ways to prevent this from happening. We will also discuss other, less common, causes of a bent spine (scoliosis) in guppies.

What Causes Bent Spine Syndrome in Guppies?

Bent Spine Syndrome in guppies has a few causes. These are mostly out of your control, but some of them can be controlled.

Here are some of the common causes of Bent Spine Syndrome in guppies.


The leading cause of Bent Spine Syndrome in guppies is from pregnancy. This is why you most often see bent spines on female guppies.

Why does pregnancy cause a bent spine?

Simple, the extra weight on the guppy from carrying 30+ fry causes the spine to fall out of alignment and bend.

There isn’t anything you can do to prevent this cause of bent spine – it just happens to some guppies. It’s more common with older females because their bones are not nearly as strong, but it can still happen at any age.


Do you have guppy fry with a bent spine?

That obviously isn’t from pregnancy. If your guppy fry has a bent spine, then that is most likely from inbreeding.

This is common in fancy guppies because they have been inbred to select for pretty colors. It also occurs when you do not add any new guppies to your guppy tank for years, which is equal to many generations due to the short gestation period of guppies.

I know this one because guppy fry with a bent spine occurred in my guppy tank after a few years of not adding any new guppies to my tank. I added a few new females to remedy the problem and the bent spines in guppy fry went away after that.


Bent spine is the guppy form of scoliosis. And just like scoliosis in humans, it’s mostly hereditary.

This means that a female with a bent spine is much more likely to pass the condition onto her offspring.

Note: This is why I recommend removing the female from the breeding population. You don’t want to create a new breed of guppy with a bent spine.

Bad Water Parameters

Bad water parameters can cause a bent spine in guppies because bad water leads to weaker, unhealthier guppies. However, this is not nearly as common as you would think.

Why is it not common?

Guppies are a hardy fish. It might occur with more fragile fish, but guppies can survive such a wide range of water parameters with seemingly no ill-effects. Though putting your guppies in a small bowl or untreated tap water may cause problems.

Sure, they will not live as long and have duller colors. But a bent spine deformity from a slightly bad water parameter?

Unlikely in a fish as hardy as a guppy.

I strongly recommend testing your water on a somewhat regular basis in order to keep your water parameters in a safe range. You can find a kit on Amazon here (sponsored link).

Too Many Guppies in a Tank

This one will cause bent spine, but not for the reason you think.

If you have too many guppies in a tank, then you will have much more inbreeding. As mentioned earlier, inbreeding leads to more bent spine deformities and other problems in fish.


Finally, chemicals in the water can cause bent spine in the offspring. Where would chemicals in your aquarium water come from?

Spraying household cleaner in the same room as your aquarium, usually.

Sadly, this usually just results in the death of your aquarium. But it sometimes can result in usual birth defects that include a bent spine or bulging eyes.

Please, don’t spray chemicals in the same room as your aquarium.

How to Prevent Bent Spine Syndrome in Guppies

[The above video describes exactly what is going on with a bent spine in aquarium fish.]

There are ways to prevent the bent spine deformity in guppies. It usually involves the breeding cycle. However, the rate can also be lowered by having clean water amongst other good aquarium practices.

This section will cover some of those methods.

Avoid Inbreeding

First, you want to avoid inbreeding your guppies.

I know, this is hard because guppies breed like, well, guppies. The easiest way to prevent inbreeding is by adding a guppy from a different genetic line to your tank every few months.

This adds some genetic variation to your strain and should drastically lower any genetic inbreeding. It will also reduce birth defects.

Remove Bent Spine Guppies from Breeding

I strongly recommend that you immediately remove any bent spine guppies from the breeding pool of your tank.

This, combined adding new genetic lines to your tank, should prevent most bent spine deformities if you follow the following aquarium guidelines.

Frequent Water Changes

This one is obvious – change out your water.

The frequency of water changes depends on the size of your tank, the amount of plants, the amount of fish, and a hundred other factors.

The simplest way to determine how often to do a water change is to measure the water parameters. If the parameters are bad, then slowly change the water.

10% per week is a good general guideline to follow. It’s low enough that it will not stress your fish, but it’s enough that it will keep the tank healthy.

Quarantine New Fish

Another good aquarium practice is to quarantine all fish. This allows you to observe any problems – tuberculosis is another cause of bent spine syndrome.

It’s extremely rare, so I didn’t mention it. Unfortunately, it’s highly contagious, which means it can easily spread to all the fish in your aquarium.

This is the main reason you should quarantine all new fish before adding them to your aquarium.

Don’t Add Pet Store Water to Your Tank

Another good practice that many beginners fail to do – don’t add that nasty pet store water to your main tank.

You should have a quarantine tank for the fish and the water. When it’s time to transfer your fish to your main tank, simply net the fish and quickly drop it in the tank.

I know, this can stress out the fish, but if you’re quick the stress is not too much. And it’s much safer for the health of your aquarium to use this strategy rather than adding a bag of questionable water to your perfect tank.

Avoid Chemicals

I can’t stress this point enough. Avoid spraying chemicals in the same room as your aquarium.

The droplets from the aerosol can drip into the water. Those droplets contain all kinds of chemicals that can cause deformities in animals as sensitive as small fish.

Even worse, they will frequently cause deformities or death in extremely sensitive aquarium animals like snails and frogs.

Should I Euthanize My Deformed Guppy?

It’s not entirely necessary to euthanize a deformed guppy – you can simply add it to a quarantine tank to live out its life. This is especially true if the deformity does not seem to impact the guppy’s ability to swim and other fish do not bully it.

Unfortunately, a quarantine tank is a lot of work, so euthanasia is usually the option most owners of deformed guppies choose.

I won’t cover the best way to euthanize a guppy as that is a highly personal decision. But please do not release your guppy into the wild. They are an invasive species in most of the world and will wreak havoc on any ecosystem they can survive in.


That’s about it for all you need to know about deformed guppies. The most common is the bent spine. Unfortunately, it does not have a cure, but most cases are minor enough that the guppy can live a perfectly fine life.

For prevention, make sure to keep the water clean and feed your guppies a diet of fortified food for bone strength.

Leave a Comment