How to Identify Koi Sickness Symptoms

How to Identify Koi Sickness Symptoms

As a pet owner, there is nothing worse than the dreaded feeling of realizing your pet is sick.

We care deeply about our animals and put a lot of effort into providing them quality, loving care so it can be hard to face that they might not be doing well.

Be it a parasite, bacterial infection, or some other issue, illnesses in fish can be especially hard to diagnose and treat since they are less able to communicate discomfort.

Let’s look at how to identify koi sickness symptoms for common illnesses to help you better diagnose your pet and prepare for treatment.

Koi Sicknesses

Koi are generally very, very hardy fish who can handle a lot.

They are not plagued by many illnesses and are, for the most part, rather healthy fish.

Still, there are some issues that may impact your koi population or individual fish in your pond.

Let’s take a closer look at a few of the most common illnesses.

How to Identify Koi Sickness Symptoms

Ichthyophthirius Multifiliis (Ich)

Ich is one of the most well-known fish diseases. Potentially infecting almost all species of fish, Ich is often associated with the presence of white spots on the body and fins.

While this is definitely an indicator of the presence of Ichthyopthirius Multifiliis, there are other symptoms you can look out for to help you more concretely diagnose your koi with Ich.

As a protozoan parasite, the disease causes a lot of discomfort for your fish.

Due to this, they may clamp their fins tightly against their body and rub against things in their pond in an attempt to scratch the white spots, which are actually holes where the Ich protozoa burrowed into their skin.

Their eyes may also look cloudy and they may appear restless while having a decreased appetite, as well, though these may not appear as symptoms in milder cases.


Dropsy is a term used to describe a range of symptoms caused by either parasitic, bacterial, or viral infections.

It can also be triggered by liver dysfunction.

As a symptom instead of an actual disease, dropsy is used as an indicator something else is wrong.

Still, it is hard to watch, as it causes your fish’s belly to appear distended due to the presence of fluid.

It can also impact their ability to swim, cause their tissues and scales to protrude, and cause them to stop eating.


There are two main types of flukes, gill and skin.

Both are dangerous and can make your fish very uncomfortable, resulting in several different symptomatic behaviors that are rather easy to identify.

Gill flukes can cause your fish to appear restless and make them gasp for oxygen at the top of the tank, leap from the water, and thrash about.

Skin flukes cause itching, lesions, rashes, scale-loss, sluggishness, thrashing, and clamped, irritated fins.

These are very uncomfortable conditions and should be remedied as soon as possible since they can actually cause death.

These parasites are definitely bad news.


Another protozoan parasite, Trichodina can cause lethargy, gasping for air, thrashing, red and painful lesions, and floating at the top of the tank or at the bottom.

This disorder can cause death and is very painful since it decreases the oxygen in your koi’s body and causes them to break out in a lesion-filled rash.

Trichodina is very contagious and can survive in colder water, making it more easily spread through koi populations, especially if your pond is highly stocked.

Anchor Worms

One of the few parasites that plague kois that you can actually see, Anchor Worms will appear as little threads hanging from your koi.

These parasites usually slide under a scale on your fish, usually near the gills, and use their anchor-shaped head to attach themselves to the fish and suck its blood.

They multiply quickly and can spread in your pond super fast, especially if your pond is highly stocked.

Additionally, they are tricky to remove since not getting the head out when pulling them off can lead to serious infections.

Other symptoms of anchor worm infestation include whitehead like bumps on the body, scratching on pond surfaces, lethargy, floating around, and thrashing, along with red spots and irritated areas.

Fin Rot

Typically caused by poor water quality and lack of temperature regulation, fin rot is a very common disease in koi fish.

The biggest, most noticeable symptom is that an impacted koi’s fins will appear to be ripped or shredded instead of one singular piece.

This can affect how the koi swims, especially if the case is severe, and even cause them to be unable to access food and other aspects of their pond.

Fin rot is contagious and makes the fins delicate so quarantine is recommended to ensure your fish does not become further damaged during treatment or spread their illness to the others within the pond.

Fin rot can also be caused by stress, so be sure your pond is not overcrowded or otherwise not safe for fish when treating your koi, as well, or else you will likely have to deal with a recurring infection.

Fungal Infections

Koi fish are prone to fungal infections.

Appearing like white, fuzzy mold or cotton puffs, the fungus usually concentrates around the mouth, eyes, or gills, but can appear anywhere on the body.

Fungal infections are unsightly and uncomfortable and pose a particular risk for spreading through your pond.

While most koi make a fully recovery from fungal infections, you still need to be vigilant in treatment to ensure your fish are happy and healthy.

Be sure to quarantine any impacted fish, too.

How to Identify Koi Sickness Symptoms

Feeling Better?

Koi are hardy fish who can come back from almost anything if provided with treatment and a good quality of care.

Due to this, you generally do not have to worry too much, especially if you catch any illnesses early and work to ensure the disease will not reoccur easily in the pond.

Good luck! Your koi will likely be just fine!