Why Is My Fish Shaking? Let’s Examine the Possibilities

Charlie Morton

Charlie Morton


why is my fish shaking

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If you’re reading this, you’ve probably noticed your fish shaking, twitching, shivering, or trembling and are wondering why they’re exhibiting this strange behavior.

Vigorous shaking in some aquarium fish is a natural courtship behavior used to impress a potential partner, but if your fish is shaking for longer periods, it’s probably a sign of an underlying health problem.

Constant quivering or trembling in aquarium fish is collectively known as shimmies or shimmying, and often indicates a serious illness that needs immediate attention.

More intense, uncontrollable shaking can be caused by seizures, which are also very serious, but thankfully very rare.

So, with no time to waste, let’s find out about some of the health problems that cause shaking and how to treat them.

What Are Shimmies?

Shimmies is a generic term referring to health conditions that cause a fish to shake, tremor, quiver, or rock back and forth, either in one spot or sometimes while swimming too.

The health problems behind the symptoms are wide-ranging, but most are quite serious. While many of these can be remedied fairly easily, shimmies indicate a fish that’s in significant distress and needs to be treated as soon as possible.

Diagnosing Shimmies

Shimmies is fairly easy to diagnose since it simply describes a range of conditions where a fish is shaking or trembling for long periods of time.

The only possible behavior that you could mistake shimmies for is the courtship rituals in some fish – especially cichlids, where one or both of the parents will shake vigorously as part of their display to impress their mate.

I used to observe this behavior in my male convict cichlids, and could even hear the water vibrating from outside the tank – the display is indeed a powerful demonstration of the strength and prowess of these fish!

The key difference between healthy behavioral shaking such as in courtship rituals, and problematic shimmying or seizures is the length of time a fish shakes, and the overall condition of the fish.

During courtship, a healthy-looking fish will shake or vibrate for around 5 seconds at most, perhaps repeatedly, but this is quite different from the constant, chronic shaking that we’d identify as shimmying, and completely different from a seizure where the fish will appear very unwell and out of control.

Why Is Shimmies Sometimes Called Livebearer’s Disease?

Of all the families of aquarium fish, shimmies most commonly affect livebearers – especially mollies and guppies. Since mollies are the number one victim of shimmying, some aquarists have also called the condition ‘Molly Disease’.

The reason that livebearers seem to suffer from shimmies so often is mostly down to genetics and water chemistry issues.

Causes Of Shimmies In Aquarium Fish

A list of possible causes of shimmying in aquarium fish.

Weak Genetics In Livebearers

Mollies and guppies are very highly bred fish that have diverged a long way from their ancestral, wild relatives.

Because breeding programs have focused primarily on producing fish that look attractive or interesting rather than fish with strong physiology and immune systems, domesticated genetic lines have tended to become weaker over the years.

Mollies and guppies are known to have a shorter lifespan and more health problems today than decades ago when genetics was stronger.

Shimmying is one such health condition that often affects these livebearers with weak genetics, although there are often other factors at play too.

Incorrect Water Chemistry

When shimmies is associated with fish that enjoy hard, alkaline water, incorrect water chemistry is often one of the main causes of the disease.

Livebearers (especially mollies) and African cichlids tend to have a strong preference for hard, alkaline water with a pH of between 7.5 – 8.5 and a hardness of between 10-30 dGH.

If aquarium water has less dissolved solids in it, and insufficient electrolyte levels, the fish may display their distress by shaking or shimmying in the water.

If left in unsuitable conditions for too long, internal organs such as the liver and kidneys can, sadly, become damaged, sometimes beyond repair.

Cold Temperatures

A generic cause for shimmying that can affect any kind of fish is when water temperatures have fallen too low. This condition is especially common in cichlids.

Although fish are cold-blooded creatures and their physiological response to cold is rather different from ours, cold water can make their metabolism slow down, causing them to hover or flit around or even appear to shiver in one spot instead of actively swimming around the tank.

A fish that’s been exposed to the cold or moved suddenly to a tank where water temperatures are lower are especially likely to suffer from the thermal shock which may cause them to shiver or shimmy in one spot.

Stress and Shock

Constant stress substantially weakens and strains the immune and nervous systems in fish, causing all kinds of health problems. Shimmying may be a symptom of a fish that is overwhelmed with severe stress, or is suffering from shock, which has caused the nervous system to break down.

In effect, the fish loses its ability to control its movements and is left quivering, much in the same way that we may shiver or tremble after a shocking or traumatic incident.

Chlorine and Toxic Contamination

Sometimes shimmies can be caused by toxic contaminants entering the aquarium water. Chemicals such as chlorine and aerosol sprays are highly poisonous to fish and even small amounts can do a lot of damage.

Fish exposed to chlorinated water may quickly develop hypoxia, gill damage, and neurologic malfunctioning – causing trouble swimming, incorrect body positioning, and sometimes random shaking movements.

It’s essential then that you always treat your regular water with a trusted brand of aquarium water conditioner before adding it to the tank.

Similarly, if you’re using aerosols in the same room as your fish tank, be sure to keep the tank lid on tight without any holes or gaps to protect against potential contamination.

Poor Water Quality

Aside from water chemistry, which we’ve already discussed, shimmies or shaking can also be caused by unsanitary, poor water conditions.

Every fish tank needs a good filter and a regular cleaning regime to remain a clean and healthy environment for your fish.

Fish that are exposed to dirty water conditions are more likely to develop bacterial, viral, fungal, and parasitic diseases, all of which can cause shimmies as a secondary symptom.

Disease and Infections

Although shimmies isn’t a disease in itself, it can be a symptom of other diseases in fish.

As we’ve pointed out, shimmies can be caused by high levels of stress and shock in fish, which almost any serious disease can cause.

Ich, velvet, flukes, dropsy, fungal infections, and internal bacterial infections are some of the most common diseases suffered by fish, which could eventually cause shimmying in serious cases where the disease is allowed to progress too far.

Swim Bladder disease is especially associated with shimmies since both conditions can cause fish to lose command of their swimming and position in the water.

In a serious case of swim bladder disorder, fish may get stuck at the top or bottom of the tank, or swim on their side, sometimes appearing to shake or tremble.

How To Treat Shimmies

The treatment of shimmies will depend on what’s causing it, so let’s take a look at how to treat each of the possible causes, one-by-one.

Treat Livebearers With Weak Genetics

While genetic problems in livebearers can’t be treated at the root level, you can include things in your care regime to help aid your fish in living a healthy, long life.

For mollies, keep tank temperatures between 72 – 80 Fahrenheit, with a pH of between 7.5 – 8.5, and offer them a diverse diet of dried fish food along with aquarium plants that they can browse on, and meaty treats such as bloodworms, daphnia, and brine shrimp to strengthen their immunity.

The best way to avoid genetics issues in livebearers, however, is to source the strongest stock you can from reputable, specialist fish breeders.

They might be more expensive than fish bought from your local pet store, but nine times out of ten it’ll be worth the extra investment.

Correct Your Water Chemistry

If you notice shimmying in your livebearers or African cichlids, the chances are that it’s being caused by unsatisfactory water chemistry for your fish. Since incompatible water chemistry can cause internal organ damage, you must act fast to correct the problem.

why is my fish shaking

The key here is to increase the amount of dissolved solids in the water and raise the water’s pH. While some fish keepers have done this with aquarium salt or Epsom salts, other methods can create more stable conditions.

Adding crushed coral substrate or limestone rocks to your aquarium is a great way to steadily maintain a higher water hardness and pH over a long period of time, as the calcium and minerals in these additions are constantly dissolving and adding to the mineral content of the water.

As a short-term solution though, aquarium salt, sodium bicarbonate, or store-bought solutions such as ‘Molly Bright’ or ‘Shimmy Blocks’ may temporarily relieve symptoms, while the limestone or coral is gradually making suitable conditions for the long term.

If you do wish to buy crushed coral, just be sure to obtain it from sustainable sources only, since it is sometimes dredged up from the sea floor which can cause many ecological problems.

Adjust Your Water Temperature

If you think shimmies might be caused by water that’s too cold, the first thing to do is to make sure you’re getting accurate readings from your thermometer. Place it away from the heater to get a more reliable reading for the average tank temperature, and then check to see if the temperature recorded matches the suitable range for your fish.

Whereas cold water fish such as goldfish prefer water that’s less than 75 degrees Fahrenheit, tropical fish from near the equator such as betta fish and neon tetra can stand water temperatures of 80 degrees or even slightly higher.

The key here is knowing the needs of your fish and only mixing species that enjoy the same water conditions.

Carefully adjust the thermostat on your aquarium heater to make the water warmer, but keep checking back on your thermometer as you do so, making sure the water never gets too warm!

Reduce Stress and Shock

Fish that are shaking because of stress urgently need tank conditions correcting to reduce the chances of their symptoms worsening and the likelihood of death following.

If your fish has become stressed because of bullying or intimidation from other aggressive fish, it’s essential that you remove either the troublemakers or the victim as soon as possible.

Choosing compatible tank mates is key. For example, boisterous, fin-nipping fish such as tiger barbs should never be kept with species with long fins such as Siamese Fighting Fish or Angel Fish.

Increasing the number of plants, rocky caves, and hiding places is one of the best steps you can take to reduce stress and injuries in your aquarium. Live plants help your fish to feel at home and give them a place to take refuge when they’re feeling threatened.

Some fish can also become stressed by constant exposure to bright lights, especially when they’re already feeling overwhelmed. Turning the lights off and getting your fish to rest is a good way of reducing stress in the short term.

In the long run, consider adding some floating plants to create dappled shade or reducing the intensity of your aquarium lighting bulbs if you notice that your fish are frequently stressed.

Remove Chlorine and Other Contaminants

Chlorinated tap water must always be treated with a water conditioner before adding it to a fish tank. But if you’ve already gone ahead and added chlorinated water to your aquarium, you need to act fast to avoid potentially fatal poisoning.

Thankfully, water conditioners such as Seachem Prime can also be added directly to the aquarium in an emergency to neutralize not only chlorine but also toxic nitrite and ammonia levels too.

It’s a good idea to have some on hand for such emergencies!

If your tank has been contaminated by soap or an aerosol that can’t be neutralized with a water conditioner, then your best bet is to perform an emergency water change of 50% of your tank’s water with safe, treated water of matching temperature, followed by 10% water changes in the days that follow until symptoms disappear.

Improve Your Water Quality

It’s a good idea to test your tank’s water with a complete aquarium testing kit once per month or whenever your fish look unwell or show unusual behavior.

Use an API test kit to check if your tank’s ammonia, nitrite or nitrate levels are higher than they should be. Also, check for strong algae growth which could indicate excessive levels of phosphate.

All of these are signs of an aquarium that’s been poorly managed and needs better filtration, more regular cleaning, and a less excessive feeding regime.

Get yourself a good hang-on-back filter, clean it at least once per month, and also perform regular gravel vacuuming and partial water changes every 1-2 weeks.

In an emergency, perform a 50% water change to replenish your tank with clean water of a matching temperature, then follow a frequent tank cleaning regime for conditions to improve.

Treat Diseases and Infections

If you’ve identified that shimmies is being caused by a disease or infection, your fish will need treatment as soon as possible for the best possible outcome.

Parasitic infections like ich can be treated at home by placing your fish in a hospital tank and gradually raising the water temperature and applying liquid medications.

Bacterial infections are best treated with antibiotics, although these are not always available without first consulting a vet.

Swim Bladder disorders, constipation, or dropsy are often treated with an Epsom salt bath or by feeding with blanched peas to clear the gut.

Each of these diseases needs careful understanding, so we’d highly recommend checking out the diseases section on our website or consulting a specialist fish vet for effective diagnosis and treatment.

Fishing Shaking FAQs

Can Platies and Swordtails Get Shimmies?

While platies and swordtails are indeed part of the livebearer family, they don’t suffer from shimmies nearly as often as mollies or guppies.

This is partly because platies and swordtails are less highly bred than either mollies or guppies and so still possess more of their wild genetics that keeps their immune and nervous systems in good shape.

Be careful keeping these two species together though. Because they’re so closely related, they can interbreed together, producing a hybrid offspring that will tend to be less fit and healthy than either parent!

Can Fish Have Seizures?

As we mentioned at the beginning, on rare occasions intense shaking in fish could be caused by a seizure.

Seizures are normally caused in fish by neurological disorders, which, according to the MSD Veterinary Manual, all fish are susceptible to. Abnormal electrical activity in the brain or a brain infection is the most likely cause of a seizure, although epilepsy is also possible in fish.

Thankfully seizures in fish are very rare because they’re also very difficult to treat. If you think your fish has had a seizure, you could try taking it to a specialist fish vet, but proper diagnosis and treatment are hard to come by.


While aquarium fish shaking in short bursts can be a healthy courtship behavior, constant shaking or quivering is the symptom of various health problems, known collectively as shimmies, and needs addressing as soon as possible.

There are many possible underlying causes for shimmies, and each one requires its own remedy to cure it.

On very rare occasions, intense shaking could also be caused by a seizure, with the underlying issues being very difficult to treat.

For more information on diseases that could contribute to clamped fins, check out our pages regarding health and disease here.

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