What it means when koi fish swim sideways and upside down.

When koi are swimming around normally you feel like everything’s good. There might come a day, however,  whenever you go out to your pond to see them swimming in ways other than straight up. What does this mean?

What it means when koi fish swim sideways and upside down. It isn’t normal for a fish to swim this way. Fish, in general, are only supposed to swim with a vertical posture and swimming any other way could be a sign of internal problems.  It sometimes points to a problem with its swim bladder but not always.

Why is my koi fish swimming erratically?

There are many reasons why your koi fish may be swimming in an odd way. This behavior could be due to parasites, predators, or bad water quality to name a few factors. These problems can cause stress on the koi which is believed to be the main cause of erratic swimming patterns.

 Swimming Sideways

Uh-oh! Somethings wrong. Your fish is swimming sideways. What do you do? The sideways swimming motion of your fish could be an indication of your fish having to cope with these issues:


  • Bad water quality


  • A swim bladder infection


  • Parasites


Water quality definitely has an effect on a fish’s behavior. Dirty water causes a lot of stress of your koi so you need a good filter installed in your pond to sift garbage out. The fish might also be swimming sideways to knock off parasites such as skin fluke worms. Swim bladder infections can be the culprit too and this would require an antibacterial treatment to solve. A product such as Melafix may be just what you need.

 Swimming Backwards

Koi carp generally have a tough time swimming backward so this might be cause for alarm. They will go backward to get to the food they missed or if they sense danger or that something is amiss. Stress could be another factor that kind of goes along with the danger category. Make sure your filter is cleaned regularly because poor water quality can lead to bizarre behaviors like this too.

 Swimming Upside Down

This is the most alarming type of swimming problem as it is not at all natural for a fish to do this. This is often indicative of an internal problem for your fish.

The swim bladder is usually responsible for this. This is the organ that allows fish to regulate pressure when floating.  A swim bladder problem due to disease (viral or antibacterial) or pressure changes can cause this behavior. 

Like the other two behaviors start with checking the water quality as a first step.

Maybe Nemo’s Just Shy!

Although koi are considered a social fish some are timider than others. Some fish owners have the fish that is still wary of their presence and will swim backward away from them during feeding time for example. So your koi might be scared of you and that may be a reason for the backward swimming they do.

Unrelated but interesting fact, most fish can swim backward with a few exceptions.  The one fish that I know can’t swim backward is the shark. This is the one fish , that I know of at least, that is not able to swim backward because their pectoral fin can’t bend upwards like other fish can. They also can’t stop on a dime to avoid bumping into something. They have to swerve one way or the other instead. It’s kind of nuts to think about such an apex predator having such maneuverability issues, but they do. Weird!

If a shy koi has something to go inside like those little castles, for example, they will back up into them when something seems awry. Or maybe it’s swim bladder disease.

The Sordid Swim Bladder Disease?

Bony fish, koi included, have an organ called a swim bladder. It is responsible for regulating the buoyancy in a koi carps body to keep it at a certain depth in a body of water. Knowing this, you probably know if it goes off kilter you will see koi floating or sinking to the pond bottom.

Swim Bladder Diseases Likely Culprit

Koi like to eat a lot. Unfortunately, overeating is the leading cause of this swim bladder disease stuff. What happens is fish gobble down food and gulp a lot of air when feeding at the surface. Koi gobble down pellets like crazy and expand as water comes into contact with it. These expanded pellets get to the digestive tract and cause constipation, which also puts excessive pressure on the swim bladder as well. That is how swim bladder disease is often incurred.

Water temperature changes can also cause problems with the swim bladder. Fish may have problems swimming in the fall and winter because of physiological changes that take place. Cooler temperatures mean slower digestion of food for koi fish. Digesting protein is the hardest when it’s cold. This buildup of undigested food can cause the intestine to become engorged.

Stressful Swimming

Stressed Fish


Anything that causes stress for your fish will affect its swimming pattern. Things like overpopulation, dirty water, change of habitat, or a change of routine can cause this anxiety. Signs of this anxiety are things such as:

  • Poor appetite


  • Gasping for air at the surface


  • Disease. White spots, called Ich, on your koi fishes body


  • Rubbing themselves on rocks or other hard surfaces

Swimming erratically in weird patterns can be an alarming occurrence. If these symptoms listed above are happening for your fishy friends then it’s a good idea to consult an expert vet to find out what your next move should be. They should be able to get your koi back upright.

Fish Not Hungry?

A poor appetite affects a fish’s behavior if it isn’t getting the sustenance it needs. Stress affects koi just like it does us. They won’t eat. This being said, a koi not eating much might not be cause for alarm. Why? Because koi don’t really have a regular feeding schedule. 

A koi’s appetite depends on many factors. Water temperature is one of those factors. Do you eat the same amount in the Winter as you do in the Summer? No! In fact, koi are hibernators in the Winter and if it’s cold enough they won’t eat hardly at all. In the Summer though it’s a different story. They are ready to eat in the warm Summer days.

If your koi aren’t eating on a warm, sunny, summer day and your koi carp are swimming crazily sideways, upside down, or backward stress might be to blame. Check with your vet.

No Air. No Air.

When I was young I used to keep goldfish. My parents bought me a bowl to keep them in. We weren’t very knowledgable about them. Anyway, I came home from school often to learn my goldfish jumped out of the bowl. What I believe was happening is they were suffocating and getting carried away with going to the surface and accidentally jumping the bowl. I eventually gave up goldfish.

If your koi are coming up panting to the surface then this doesn’t mean they are trying to make a social call.. Your koi are suffocating. Gasping for air is a problem that can happen when the oxygen count is low in the pond. This is stressful on the koi in your pond. Your fish are gasping because they have to get their oxygen from somewhere.

Fish usually take the dissolved oxygen from the water in order to breathe. Gasping for air at the surface is a survival tactic because they are suffocating. You can fix this by ensuring that you have good aeration throughout your water. A fountain is one way to do this.

Whenever your fish isn’t breathing, of course, it is stressful for them. This also causes a weakened immune system which is another stressor on top of that. Let’s just also pile on the inevitable fact that a fish not breathing could kill him/her, not to mention causing problems with swimming gracefully. So buy a fountain to break up the water and keep oxygen saturating the H2O in your koi pond.


Don’t go about solving the problem of your fish swimming irregularly by automatically blaming it on disease. As you have learned already there could be other simpler culprits. Maybe it’s our inclination to blame disease because of our country’s medical system(but that’s another article I’m not qualified to write) or who knows. Something makes us automatically blame weird swimming patterns on something being wrong with your fish.

Now you know better, Right? Good.

I will say I am not a vet. I have 0 veterinary credentials to present. So the best advice to rule out disease is to contact a vet experienced in working with koi. It isn’t bad to cross disease-check of your to-do list.

Are Your Koi Rubbing Themselves on Rocks?

Your koi scratching themselves on rocks could be a result of parasites. When they itch, they rub. The way bears rub on trees to relieve their itches. Koi don’t have Caladryl available, so they have to relieve themselves with what they have. 

If you want to solve this problem then open your pantry. The ingredient that fixes the itch is in at least 99% of all households- regular table salt. A parasite called Ich is usually the cause of your koi itching and table salt is added to your pond at a rate of 1 pound per 100 gallons of water each day until the ponds percentage is .4% salt. 

If you notice these odd swimming behaviors then the first thing to do is check the water quality. You can often save time and money doing this first. The acidity level should be checked. The normal pH range is from 6.5-9.0. You can purchase pH testing kits online to do this. Ensure that the pond filter is working well too.

Image by Hardy Peters from Pixabay

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