Common Koi Fish Diseases and their Treatments

Koi are one of the toughest and most resilient fish that rarely gets sick. But this only happens if they are kept in ideal conditions. If conditions become poor, you will find them getting sick frequently and developing Koi fish diseases.

Many koi fish owners know many of the signs and symptoms of sickness, hopefully we can teach you a few more! If you are someone with a sick Koi, this article will tell you everything you need to know about common Koi fish diseases, their diagnosis, and remedies.

How to Know If Your Koi is Sick?

Your top priority should be to keep your fish healthy and alive. It is an undeniably considerable amount of work that will take your time and patience. But, to do so, you must keep a close eye on any of the following signs they might exhibit.

1. Poor/non-existent appetite
2. Isolating itself from others
3. Erratic swimming
4. Acting lethargic
5. Gasping at the pond’s surface
6. Hanging near the surface or waterfall
7. Rubbing itself on the pond’s walls
8. Flashing
9. Red streaks on the fins
10. Ulcers
11. Clouded or popped eyes
12. Swollen abdomen
13. Raised scales
14. Red congestion around the gills, scales, and mouth
15. White spots
16. Grey or yellowish mucus on gills
17. Ragged fins
18. Fluffy cotton-like tufts

What to Look for When Analyzing Your Koi?

When evaluating what is wrong with your Koi, consider the following four factors:

1.      Feces/Waste

• Examine your Koi’s feces/waste. See if it is floating and gelatinous or sinking and dissolving in the water.
• If it is gelatinous and does not dissolve immediately, your Koi has indigestion from a scrape on the intestinal lining.
• Low-quality food consumed by your Koi and harmful debris in the pond can cause scraping.

2.      Water Purity

Ensure your water quality is up to par. Anything less than optimal might kill your fish. If you find your fish in general discomfort, check this component first.

• If your pond water is muddy or cloudy with high turbidity, it is unhealthy, and your fish may find it challenging to obtain optimal oxygen.
• Check the ammonia and nitrate balance. If you find it is not optimal, take quick action to improve it. 

3.      Physical Body Examination

• Look for any opaque mucous, wormhole-like appearance on the scales or a parasite.
• If you find a parasite, examine it under a microscope, if available, to see its shape.
• Run your hand down the body of your Koi; if it has lost its slipperiness and has grown dry, it is most likely chilodonella, gyrodactylus, or dactylogyrus- organisms that reside on the fish’s skin.
• If you find the scales have risen from the body, this indicates a pinecone disease.

4.      Koi’s Death Pattern

A massive die-off indicates that the disease has spread throughout the pond.

Observing the mortality pattern can aid in diagnosing the sickness and its prevention before it spreads.

• If you introduced a new Koi into your pond without first quarantining it, there must be a parasitic infection brought in by the new Koi.
• Toxic elements in the water can quickly kill Koi. If there has recently been heavy rain, construction, or remodeling around your pond, hazardous chemicals that seeped into the pond probably disrupted its environment.
• Water sources with high chlorine levels can cause a disease outbreak in Koi.  
• If you notice no anomalies in your Koi’s behavior or physical appearance but see a mass-die off, your Koi is most likely infected with herpes, columnaris, or bacterial infection.

6 Common Diseases and Their Treatments

Once you are aware of the problem affecting your Koi, the next step is a treatment strategy to guarantee that the fish does not die or spread the disease to the rest of the school. Six most common Koi diseases and their treatments are listed below for quick referral.

Disease	Symptoms	Treatment
Anchor Worm – A rod-shaped 3mm to 12mm parasite.	Red congestion around the infected area, tight skin, white mucus discharge, and epidermal cell proliferation.	Removal with tweezers and medications. To kill Anchor worm’s larvae, use Trichlorfon ( 0.2 – 0.5 ppm, twice every 2–3 weeks).
Ich	Tiny white spots appear first on the head or pectoral fin, then spread throughout the body. Infected Koi sinks to the pond’s bottom, loses appetite, hangs beneath the water’s surface, and become lethargic.	Isolate your Koi and begin bath treatment with higher salinity levels (0.5%-0.6%.) Warmed water with a temperature of at least 28°C (82°F).
Argulosis – Fish lice	Erratic swimming, scrapes the pond sides, flashes, wiggles the pectoral fins, and shakes their dorsal fins.	Remove lice with tweezers and medicate. To kill fish lice larvae, use Cyromazine or Trichlorfon (0.2–0.5 pmm, twice every 2–3 weeks).
Columnaris – gills, mouth, and fin rot.	Loss of appetite, drowsiness, congregation around the water’s edge, emaciation. Mucus on the body that is cloudy. Scales and mucous are shed. The disease can cause mortality and must be caught early.	6–7kg (13–15.5LB) of salt /t (264 gal.) for 5-7 days. 5-6kg/t (264 gal.) oxytetracycline with salt for 10 days. For 10 days, use 5-6 kg/t (264 gal.) of oxolinic acid with salt.
Dactylogyrosis, Gyrodactylosis – Fluke	Koi scratch itself against the pond’s walls, become anorexic and lethargic, and their eyes become bloodshot.	3g of potassium permanganate / t (264 gal.) every two hours.
Chilodonella	Infected fish roll on their sides and swim erratically. The loss in appetite can potentially kill Koi.	For two weeks, increase the salt concentration in the pond. Aeration should be increased.

My Koi is Infected Now- How do I save it?

Once you have determined what disease your Koi has, you must act promptly to restore health and prevent the disease from spreading. There are two ways to keep your Koi from dying:

1. Parasites can be removed by tweezers.
2. If you are confident that the water quality in your ponds is good and that no other fish are sick, you can quickly quarantine your sick fish and provide it bath treatment. It allows you to focus on one fish that requires special care while saving others from a potential outbreak.

Preventative Measures for Better Koi Health

Instead of having to take care of sick Koi, maintain a task schedule and take precautions to ensure that your fish and pond do not reach a point of infection. These a usually easy and simple tasks.

1. Ensure that the food you are feeding your fish is of high quality and your fish does not eat debris from the pond.
2. Use biological pond filters to keep your pond’s water quality up to par. Perform frequent water tests to maintain a balanced atmosphere in your pond.
3. Consider installing a waterfall. Moving water is high in oxygen and keeps the pond well-aerated as well. Aeration is key for koi health; they require 6 mg/L for proper health!
4. Because diseases can quickly spread in the pond and affect the entire school, quarantining any new fish before introducing it to the pond can help prevent a catastrophic disease outbreak.