How to Tell if Koi Fish Are Stressed?

-- By Carol

Like most aquarium fish, koi can also get into stressful situations and often find them challenging to cope with.

As a koi fish owner, it is essential for you to identify the signs and causes of why your koi is stressing out so you can get it treated immediately.

Keep reading this guide to discover: “How to tell if koi fish are stressed out?”

Table of Contents

Signs Your Koi Fish is Stressed Out

It would be best if you were on a constant lookout for identifying the signs and symptoms of stress in your koi fish.

Some fish are better at dealing with stress. Therefore, you should quickly identify a stressed-out koi to get it the help it needs.

Here are the most common signs that indicate your koi fish is under stress:

Your Koi Fish Will Try to Hide

One of the first things you would notice about a stressed koi is a shift in behavior, such as a lack of activity or hiding.

Stress can cause fish to separate from the school and look for a safe place to hide. Thus these behaviors may be an indicator of that.

Fish shelters and pond vegetation can provide cover, but you can also spot them idly cruising your pond’s deepest part.

It is likely your koi fish feel most secure in these locations, so that’s where they’re going to take a break from the chaos and recharge.

Because of this, it’s possible that you won’t even see your koi at feeding time, as they may choose to eat in peace and quiet while you’re not there.

These signs may indicate a change in the pond’s water quality, the presence of a predator, or simply that the fish is still getting used to its new surroundings.

Your Koi Fish Will Stop Eating

Another common symptom exhibited by stressed-out koi fish is lack of appetite.

If you start noticing any sudden behavioral changes in the amount of food your koi eats or stops eating, it could mean your koi is stressed out.

Besides this, you might notice that your koi fish is not reaching the top of the surface for food.

They may feel hungry and crave food but be reluctant to swim on top of the water tank to get it.

Your Koi Stops Following the Regular Swimming Pattern

If your koi fish is stressed, it is common to see a visible difference in their swimming pattern.

You will suddenly notice that your koi fish has suddenly started swimming in a strange manner.

This is what your koi might do when they are stressed out:

Swim frantically in weird directions
Swim sideways or tilt on the side while swimming
Swim upside down
Swim at a slow pace while staying at the bottom of the tank
Swimming in secrecy, hiding behind plants or gravel
Crashing on rocks and plants while swimming

If you notice these differences in your koi fish swimming, it is a clear-cut indication that your koi is stressed out and needs urgent attention.

If you also notice your koi fish rubbing against rocks or toys in the tank while swimming, it is another symptom of stress.

Your Koi Fish has Rash or Patches on the Skin

Symptoms of a bacterial or parasite infection include changes on the skin like rashes, sores, or patches on your koi fish.

If you notice pink patches or spots all over your koi fish, specifically their fin area, it is a significant cause for concern.

Rash and patches on your skin mean your koi is stressed and needs urgent treatment.

Also read: Why Is My Koi Fish Losing Scales?

Your Koi Fish Gets into a Fight with Other Tank Mates

Some koi fish tend to get aggressive when they are stressed.

As koi fish are generally friendly, it could be because of stress if you notice them fighting with other tank mates.

Alternatively, you may notice injuries on your koi fish. A fish that is preyed upon may also have wounds, torn scales, or broken fins.

Sometimes it is wise to delicately net your fish to the surface to check if you feel a predator may be the reason for the stress.

If they are hurt and need medical attention, a soft koi sock net can be used to contain them while they are handled safely.

Your Koi Fish Is Sick

Parasites and infections are just a few examples of diseases that can cause noticeable changes in the look and behavior of your koi fish.

If you notice any white spots on your koi fish, discoloration of scales, or other open wounds or cuts, your koi fish has a parasite attack or is sick.

Most parasite and infection treatments are safe and may be administered whenever the slightest suspicion of an issue arises.

Some koi keepers like to treat their fish for parasites and diseases towards the start of winter and after its end to ensure their fish have a healthy hibernation or start the new year.

Also read: Dropsy in Koi Fish (Bloating) – Symptoms, Care, Treatment!

Your Koi Fish Appears Duller in Color

Koi fish are famous for being bright and colorful, and that’s what makes them an excellent aquatic pet.

However, if you notice that the vivid colors of your koi fish are not bright and vibrant like before, it could be a sign of stress.

Keep an eye out on your koi, and if you notice consistent color fading, you may need to take your koi to a vet to get it treated for stress or any other disease.

Reasons Why Your Koi Is Stressed Out

Let’s now have a look at some of the possible reasons why your Koi fish may be stressed out.

Your Koi Cannot Acclimate to the New Tank

A lack of beneficial microorganisms and perhaps excessive levels of chlorine and chloramine in new ponds might be what is causing your fish to become stressed out.

There is always going to be some degree of stress for fish that are moved to a new location.

In most cases, this kind is normal, and your koi will grow to feel more comfortable in their own skin as time goes on.

Fish will often avoid their new surroundings for at least a few days and may only start eating again after you’ve left the pond.

If, after a week or two, your koi are still hiding, it’s an indication that the water quality in the new pond is unbalanced, and you should work to correct it.

A new pond’s inhabitants might be put through less strain if proper cycling procedures are followed before the fish are introduced.

Also read: How to Acclimate Koi Fish to New Tank/Pond?

Your Tank Water is Poor in Quality

For the sake of your koi, it is important to keep their surroundings as consistent and stable as possible.

The stress caused by a decline in water quality can be mitigated if it occurs gradually rather than suddenly.

The most prevalent causes of water quality stress are fluctuations in waste substances such as ammonia, nitrites, pH, and KH.

Even though these things develop slowly, they all require attention before they reach a critical stage.

Koi are particularly vulnerable to abrupt shifts since they are unable to prepare for them and hence experience extreme distress.

Your Koi Has a Serious Illness or Injury

Stress in fish can be brought on by a variety of factors, including bacterial illnesses, parasites, physical trauma, fin/tail rot, flukes, lice, or tapeworms.

Your pond should be treated to avoid the growth of hazardous germs. These germs can especially spread if your fish is injured and take advantage of their vulnerable state.

These remedies are often effective against a variety of bacterial infections, such as fungal infections and fin and tail rot.

Your Koi Fish Is Scared of a Predator Attack

If your koi fish feels threatened because of predators in the tank, it could be one of the primary reasons why your koi fish may be stressed out.

Koi fish are generally friendly and calm in nature, and they do not get aggressive with other fish mates; however, if there are any predators in the fish tank that may be harassing your koi fish or trying to get into a fight with them.

Koi fish’s common predators are herons, cats, hawks, etc. are known as common koi fish predators who may harass them every now and then.

If a koi fish gets attacked or harassed by predators, you will usually find it hiding at the bottom of the tank to avoid getting into a fight with them.

Besides this, also watch out for signs of injuries, spots, and blood marks on your koi fish if there is a predator in the tank.

You may need to take your koi fish urgently to the vet if it is under a serious attack.

The Bottom Line

Now that you know how to tell if your koi fish is stressed out, you are better prepared to deal with the situation.

If your koi is under stress, you need to quickly get it treated by changing the water, tank, or seeing a vet.

You may discuss the situation with the local vet if your koi do not get better in a few days. Best of luck!

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