Noticing your koi swimming unusually or erratically can be a very concerning sign, and it is certainly a symptom you should closely monitor to ensure things don’t worsen. Luckily, in most cases, odd behaviour isn’t always serious and symptoms usually improve naturally over time.
Strange swimming behaviour is often noticed during times of stress, such as when a fresh fish is introduced to a new environment. In fact, stress is one of the leading causes of behavioural changes ornamental koi, but the problem with stress is that it’s almost always a symptom of another underlying issue, and it doesn’t just occur on its own.
Depending on the type of swimming behaviour you’re seeing, you may need to treat the pond with medicine, improve environmental conditions, or things may just improve naturally in time. Some of the more common causes of swimming behaviour in koi are listed below:
- Swimming Backwards behaviour could indicate a number of issues, such as stress, shyness, poor water quality, or even parasites. Even though swimming backwards is not common for fish, they’ll still backup if they notice danger, a threat, or something not to their liking. If there are predator problems, this may become a more common habit, or if they have parasites, they may start backing up in an attempt to “escape” the problem. Poor water quality may also affect a koi’s behaviour, with them becoming more stressed as conditions worsen.
- Swimming Sideways behaviour could be another indicator of stress, but in this case it is more likely caused by poor water quality, parasites, a swim bladder infection, or a combination of the three. Koi that swim sideways may be performing this motion to try to rid themselves of parasites on their scales and gills, such as skin/gill fluke worms. If you also notice they’re rubbing against the pond liner, then it’s a clear sign that you have parasite problem. If the sideways swimming behaviour is accompanied by buoyancy issues, it could indicate an infection of the swim bladder, called swim bladder disease, which would require antibacterial treatment.
- Swimming Upside Down behaviour is often the most serious symptom when it comes to swimming behaviour, as this often indicates a problem with the koi’s swim bladder. The swim bladder is what your koi uses to regulate pressure while floating, and changes in pressure or disease (viral or bacterial) can cause the fish to lose control of this function. Although worsened by stress and poor water quality, upside down swimming isn’t a natural reaction in fish and is often an indicator of internal problems. If you notice your koi has lost most of it’s buoyancy control and does not ever swim normally, it’s likely the swim bladder. If the strange swimming behaviour is random, and there is periods of normal swimming, it may instead be related to very poor water conditions (i.e. ammonia poisoning).
Will My Koi Get Better Without Treatment?
It depends on the cause of the behaviour, but sometimes a koi will indeed improve naturally over time. For example, if you’re noticing strange behaviour and swimming when a new fish is introduced, it could just be the “system shock” and stress associated with the new environment. It can take a few weeks for new fish to become completely content in their new home, so as long as symptoms are not severe (upside down swimming), a small amount of strange behaviour is expected for new arrivals.
However, in many cases, especially where a koi is swimming sideways or upside down without improvement, you’ll need to step in as a fish keeper and take control of the situation. If the behaviour has been happening for more than 24 hours, you can think about attempting treatment or call a professional vet for peace of mind.
If the cause is stress from poor water quality or things in the environment (predators), only you will be able to treat this and improve conditions. If the cause is an internal infection or parasites, a vet would be able to diagnose this but you can also try to treat yourself with a wide-spectrum anti-bacterial medicine or parasite treatment.
What causes Swim Bladder Disease in Koi?
Swim bladder disease is common in the aquarium hobby, especially with certain species of fish, such as fancy goldfish. Koi carp can also contract swim bladder disease, although this is much less common in comparison with goldfish. The disease itself is still a mystery to experts, with leading causes ranging from genetics, constipation, gulping air, liver disease, and internal cysts. Parasites and bacterial infections can also cause issues with swim bladder disease, with these being the most common in koi, alongside constipation and poor nutrition.
Constipation is said to be caused by overly nitrate-rich food, or while gulping for air on the surface while eating, leading to nitrate ingestion. In cases such as this, switching to a low-nitrate fish food which sinks instead of floats may be all your koi needs to recover. Testing water quality and reducing nitrate levels will also help, as koi will be taking in free-swimming nitrates while feeding around the pond.
The next leading cause in koi, parasite and bacterial infections, is more common than constipation, and tends to occur most frequently around winter. This is because koi hibernate (enter torpor) during colder weather and their immune systems are naturally lower, meaning they’re more vulnerable to infections from parasites and bacteria that could interfere with the swim bladder.
In fact, if you start noticing odd swimming behaviour come spring, it is very likely being caused by parasites or bacteria your koi has contracted over the winter season. The best way to prevent this is to make sure your pond is safely “winterized” in time for their annual hibernation (technically, “torpor“) period.
Should You Quarantine Sick Fish?
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Quarantining your fish isn’t always necessary as most behavioural problems aren’t contagious, but it can be helpful for keeping an eye on your fish during recovery and for certain treatments. If your pond is experiencing very poor water conditions, or a single koi has parasites, quarantine can be very useful while you treat the problems in the main pond.
Since a stressed koi will naturally prefer to be alone anyway, usually swimming away from the main group, they may appreciate the alone-time in a separate stock tank as they get themselves back to normal. Quarantine is down to personal preference, but we would advise it for swimming problems caused by parasites or infection, as some treatments, such as antibiotics, are only effective when used in a separate holding tank.
Quarantine is also very useful for new fish introduced to a pond, as this allows you time to monitor them for any parasites, sickness, or problems they could bring to the main system.
With that said, quarantine isn’t always necessary so long as you carefully monitor your fish and attempt to improve conditions quickly. A stressed koi will keep away from the group naturally, so it’s often easy to monitor a sick fish even in a heavy stocked koi pond without a stock tank.
How to Treat a Koi Fish Swimming Sideways, Vertically, Upside Down or Backwards
Step 1) Test Water Parameters for Problems
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- Measures ornamental pond pH balance, Ammonia content, Nitrite levels and Phosphate content
One of the first things you should do when you notice any kind of behavioural change in koi is test your water quality for problems. Poor or degrading water conditions may not only be causing the strange behaviour, but also making it worse by increasing stress on your fish. Water can be tested using a wide range test kit which provides measurements on a variety of useful water parameters.
Common culprits of stress in fish include high ammonia and nitrites, as well as swings in KH and PH. Ammonia is highly toxic to fish, and can cause burns to the gills and scales if water concentration is high. The problem with degrading water quality is that it’s usually a downward spiral, with a small problem soon becoming a major one whilst also throwing other elements out of balance.
For example, KH acts as a water buffer for maintaining pH levels, and if this changes so does the pond’s pH reading. Water pH directly effects the toxicity of ammonia in water, with a rising pH making it more and more potent to fish.
Testing water quality is an easy way to figure out if you have a problem, and even if it’s not the root cause of their swimming trouble, improving quality will only help with their recovery. For more information on testing water and what measurements are ideal, check our dedicated article on this here.
Step 2) Treat the Pond for Parasites
- Koi Pond Treatment for Fluke parasites
Since one of the more serious causes of swimming disorders is possible infections, it’s good practice to treat the pond for both bacteria and parasites to prevent any problem progressing. Most of these treatments are safe for fish and wildlife, and will not interfere with water quality, so we recommend applying them if a koi does not improve within a few days of first symptoms.
For parasite treatments we recommend Aqua Med’s Aqua Prazi products which kill a range of parasites, including gill flukes and internal tape worms. Aqua Prazi’s treatment contains 100% pure Praziquantel, which is a well documented medicine for killing a wide range of external and internal parasites.
There are no other ingredients included which can interfere with water quality, and the treatment is safe for koi and won’t place stress on the system if dosed correctly. We recommend treating the pond with Aqua Prazi if koi are swimming strangely for more than a few days, or immediately if you notice them rubbing against the pond liner as this is a clear sign of parasites on the skin.
Increasing the salinity (salt) of the water has also been popular in the past for treating parasites, but we find this less effective for koi as they cannot withstand the high salt concentration for treatment to be effective. This is more suited for sturgeon, as they’re naturally able to survive in a higher concentration of salt water compared to other pond fish.
Step 3) Treat for Bacterial Infections
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Alongside parasite treatment, you may also need to treat the fish with antibacterial medicine to prevent any bacterial infection from spreading. The problem with antibacterial treatments is that swim bladder disease is internal, and many products only treat external infections and won’t work internally.
The only way to solve this would be to quarantine the sick koi in a separate stock tank and begin a 5-7 day antibiotic treatment procedure. If parasite treatments do not work, it may be easier at this point to have a professional vet look at your fish. However, if you have a holding tank you can treat the fish with a wide spectrum antibiotic, such as Minocycline or Kanamycin, which will both kill internal bacteria over a 5-7 day treatment period.
In terms of products, we recommend either Maracyn (Minocyline) or KanaPlex (Kanamycin) for internal bacterial infections. For Maracyn, the dosing is 2 packets per 10 gallons of water the first day, and 1 packet per 10 gallons the following 5 days. The treatment is added directly to the water, and preferably, you’d want a quarantine tank below 100 gallons or you’ll need to buy a LOT of packets for the treatment to be effective. This product cannot be applied directly to the pond, as unlike natural antibacterial treatments, antibiotics CAN cause issues with the ponds eco-system.
Alternatively, the treatment KanaPlex can be bond directly to koi food using a binding agent, such as Seachem Focus. Binding medicine to food helps ensure 100% of medicine is being adsorbed, which can be useful if you’re treating outside of quarantine. 
A natural antibacterial treatment, such as MelaFix, can also be added directly to the pond to combat external infections, which may be useful alongside a parasite treatment if the problem isn’t swim bladder related.
Step 4) Switch to High Quality Sinking Koi Food
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Poor nutrition or nitrate-rich koi food may be the cause of a bladder infection or even stress causing the fish to swim strangely. In regards to swim bladder disease, research has found a correlation between excess nitrates in the water and food and swim bladder problems.
As well as this, poor nutrition in general will lead to unhappy and sickly koi which may begin acting strangely or become more vulnerable to infection and parasites. Koi gulping for air at the surface while eating could also be a culprit, so we recommend switching to a quality sinking food pellet until symptoms improve.
Food with garlic is useful as it acts as a natural parasite deterrent, and you’d want a high quality food with a good vitamin and mineral profile for immune support. Floating pellets are more common to purchase, and it’s tough to find a sinking pellet with a suitable nutrition profile. To solve this you can place your floating pellets in a bucket of water until they become waterlogged and then add the water to the pond with the food after they begin sinking. It’s a little more time consuming, but this trick is useful if you don’t want to switch to a sinking pellet from your current feed.
In terms of food choice, for floating pellets we recommend Hikari Saki Growth as it contains a large amount of high quality protein (~40% fish meal), as well as a good vitamin profile, alongside garlic and brewers yeast. The high amount of protein will help with recovery, with the garlic combating parasites and brewers yeast helping with digestion and immune support. The pellets are floating, however, so you may need to add them to water and allow them to sink before adding to the pond.
For sinking pellets, Ecological Labs Sinking Legacy Food is a good choice as it contains a fairly high protein content (36%) from fish meal as the 1st ingredient, and also has a good vitamin profile alongside. They don’t contain garlic, but have a decent nutritional profile for a sinking food if you don’t like the idea of sinking them beforehand. For more options of top quality koi foods, check our main article on this here!
Step 5) Reduce All Possible Causes of Stress
Changes in swimming behaviour and personality (i.e., becoming shy) may be a problem originating from stress within the environment. Even though stress can be induced by poor water quality, parasites, or infections, this isn’t always the case, especially when symptoms come and go. For example, your pond may have problems with predators which you haven’t noticed, as many predators tend to visit early in the morning and late in the evening. A regular visit from a heron or raccoon will eventually lead to fish becoming nervous about visiting the surface water, which can present in their behaviour.
If your pond has no hiding places for fish to de-stress, they may start hiding away from the group as they try to recover. Poor water filtration may also be a cause, which is directly related to degrading water quality and clarity. If you don’t maintain your filtration system, or if the pond is under-aerated, water quality will decrease and koi will become less and less happy.
If you’re introducing a new fish to the pond you should expect some odd behaviour until they get used to their new environment. It can take several weeks for a new koi to find its feet in a new pond system, and it’s always good to provide lots of hiding places for koi as they settle in.
Lack of aeration may also be a problem, and your koi may be gulping for air to breathe due to lack of water oxygen! Although this is an extreme, it could occur during an event such as an algae bloom where oxygen will be quickly depleted over a short period of time.
Even if the root cause isn’t stress related, lowering stress of your fish will still help with general recovery no matter the problem. Making sure there are hiding spaces, predators are deterred, filtration is good, and your pond is well aerated will all help improve happiness of koi.
My koicarp are swimming all grouped together and jumping very high in the pond. Some of the bigger ones are losing their scales. Please help.
Hi Margaret,
Have you performed any water quality tests recently? Also, do you have any equipment providing aeration/oxygenation?
It sounds like you may be dealing with either a substance imbalance (high ammonia, pH change), or an extreme lack of dissolved oxygen – both of which are very stressful to fish. If the weather is particularly warm, and you’re not running any dedicated aeration equipment, such as an air pump, my guess would be your water is not sufficiently oxygenated.
Check below for more info on these topics:-
https://pondinformer.com/best-pond-water-test-kit/
https://pondinformer.com/best-pond-air-pump/
The common swim bladder disease that attack goldfish is constipation because of the design of their body their digestive systems are compressed in a small round body
Hi Giobel,
That’s interesting! Thanks for the comment and for sharing your experience.
One of my koi spend most of time on the bottom on his side Has done for 3 seasons Does come up to feed goes around in a circle on his side summer & winter My wife wonts me to do something but what The other fish are fine
Hi Dave,
It sounds like the koi is having issues with it’s swim bladder, which could have been caused by injury, infection, or even old age. It’s difficult to know the correct course of action without seeing the fish, so I’d certainly recommend contacting a local veterinary professional or pond consultant who can properly examine the fish in person. Although fish can sometimes survive with swim bladder issues for a long time, they often continue to get progressively worse and the fish will eventually start to suffer. It’s always best to try to treat these kinds of issues early so there is no long-term damage and the fish still has the energy to properly recover!
I’m normally a tough ol’ guy but when all seventeen of my fish died in my pond today I feel like I let them down somehow. Maybe too much vegetation. Maybe over fed. Maybe poor water quality. Maybe not enough oxygen. Two and half years raising these guys; now there all dead. I know things die but it still hurts when you try your best and the worst happens. Sorry guys! đ
Hi Dennis,
I’m so sorry that happened! Losing fish is never easy :/ I would most definitely test your water quality to see if that perhaps had anything to do with it.
Youâre not supposed to feed your fish during the winter. Let them hibernate. They canât digest the food when itâs too cold and that can kill them. Youâre also supposed to only feed them what they can eat within a minute. Anymore than that it can poison the pond as it just adds to the waste. Iâve had my koi for years and I just follow these simple steps plus I have a very good filter and water features.
I know that pain, itâs an awful feeling that punches me over and over in my gut.
Came home in March to 32 full sized koi. ( I had them for over 12 years) the weather was sporadic, freezing one week then 70 degrees and freezing. My fish were stressed out. I walked over to check on the pond to make sure everything was working properly, thatâs when I seen dead koi and a few others still gasping. It was horrific as Iâm still haunted from that experience. I literally filled the pond in. Waited about 5 more years and now I have a less than a yesr d pond. Today one of the babies was spinning. Iâm pretty sure itâs from the horrendous amount of rain that we have had. All of the others are fine. I have the one fish in quarantine. Fingers crossed.
yea its awful any creatures you do your best with birds fish any little living thing but in your case twice as much ,cause they are really expensive maybe some one could help and give you a few [cheap ] to help you get started again . good luck
Would adding pool salt to the pond help with these issues by soothing the Koi
Hi Rob,
Thanks for reading!
Adding some salt (dissolved first in a separate tub of water) may help some with stress, as stressed fish tend to have electrolyte imbalances as a result of said stress. However, as far as I’m aware it won’t help with the actual swim bladder issue.
My Ghost carp is swimming on one side and laying on the bottom of the pond on his left side always his left side, and when he try’s to swim it’s always his left side as well. You can see him trying to right himself but is ok for about 3 seconds then back swimming on his left side again. He is eating well, but is now over 15 years old.
Any help would be good.
Thanks
Hi!
My koi is swimming sideways, either at the bottom or at the top of the pond. Would it be better if we place it on a separate aquarium? How can we treat it naturally if we don’t have any medicine?
Please help. đ Thanks.
My koi is upside down at the bottom of the tank? He is one of five in the tank and we have isolated him and changed tank water. We have been out of town and come back to odd behaviors from him and some red sores on his back fin and a build up of stuff along his fin that another koi was trying to rid him of. Please help me find whatâs best for him. Theyâre like my children, I canât let him die or be in pain.
Hi Melisa,
I’m sorry to hear about your koi. It sounds like he might have a swim bladder disorder, which can cause him to lose his buoyancy and float upside down. This can be caused by overfeeding, poor water quality, or bacterial infection. The red sores and the build up of stuff on his fin could be signs of fin rot, which is also a bacterial infection that can damage the fins and scales. You should consult a veterinarian who specializes in fish diseases as soon as possible. They can diagnose the problem and prescribe the appropriate treatment for your koi. In the meantime, you can try to improve the water quality by doing frequent water changes, adding aquarium salt, and using a filter with activated carbon. You can also try to feed your koi a pea that has been shelled and cooked, which can help relieve the pressure on his swim bladder. I hope your koi recovers soon.