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3 Common Koi Fish Diseases In Backyard Ponds

Koi fish diseases are easier to spot if you become familiar with your koi’s behavior. You can learn to spot the common symptoms. Here we will cover these 3 koi fish sicknesses: anchor worm, white spot disease, and fin/mouth rot.

Melissa is terrified that she did something to hurt her precious koi fish.

Some are moving slowly, almost like they are going in slow motion. Others are rubbing their scales against anything they can swim near (flashing). She also hasn’t seen much of Elvis Fishley lately. He’s her favorite but recently he’s been very shy, almost like he and a couple other koi are hiding.

She takes a closer look and immediately knows something is wrong.

A few of her koi are swelling up like little balloons. Others have swollen eyes, missing fins, discoloration, and other issues. They are definitely sick, and not with the same disease.

She needs to find out what is attacking her poor koi.

Learn all about fish for backyard ponds >>

Melissa walks back inside her house. She immediately sits down in front of her computer and opens up her Internet browser. She wants answers and she wants them now. If her fish are in danger she wants to know before she starts calling every veterinarian, fish doctor, or whoever might be able to help.

After a few hours of research, Melissa comes up with 3 diseases that are the likely culprits.

These are 3 common koi fish diseases pond owners see in their backyard water features:

(clicking the links above will scroll this page down to that disease)

Let’s take a look at what each of these koi sicknesses looks like and possible treatments.

1. Anchor Worms

A few of Melissa’s koi fish are showing symptoms of having anchor worms.

They are shaking their dorsal or pelvic fins, swimming oddly, and jumping out of the water a lot more than normal. They are also flashing against anything they can get near.

She takes a closer look at a few and sees white, stringy worms near the base of some of their fins.

Fish pond illnesses- parasites

These worms are causing red sores and inflammation on her koi. They look sore and painful. Her research leaves her with a sense of frustration. How was she to know her new plants or fish were possible carriers?

She needs parasite medication and tweezers to remove them.

2. White Spot Disease

Melissa also sees koi with white spot disease.

Like the name imples, some of her koi have small white spots appearing all over their scales. They’ve also been gasping for air while clamping their fins close to their body. All of the ones with white spots are flashing and swimming oddly.

Pond fish illnesses- fish with white spot disease (ich)

Also known as ich, this koi fish illness often occurs due to pH unbalancing or rapid temperature changes.

Sometimes it can get into a pond by piggybacking on other fish or plants. The white spots are actually tiny parasites. They start on the fins and can eventually take over the entire fish.

Melissa reads that she can treat her fish with antibiotics in a separate tub of water.

3. Fin/Mouth Rot

Melissa can see a few of her koi literally rotting away.

They don’t swim near the other fish. At feeding time they stay near the bottom of the pond. It just seems like they don’t want to do much of anything besides be near the waterfall.

Fish with fin rot disease
Picture courtesy of André Karwath aka Aka

She sees it goes by many names: fin rot, mouth rot, gill rot, and dermal rot.

Whatever you want to call it the symptoms are similar:

  • Koi looks like it has white rags on as scales and mucus come off
  • Fins or mouth start breaking down
  • Fins start changing colors, usually to some combination of white, black, or brown

This bacteria could have gotten into her pond due to many reasons. Her filters may not be working well, their may be too many fish, or the oxygen levels may be too low.

To treat it, Melissa must isolate her fish in a tank. Then she’ll treat them with antibiotics.

Treating Koi Fish Diseases

Melissa sees that treatments can vary depending on the type of koi fish illness.

The first step is always to identify what it is because giving your fish the wrong medication will, at best, have no effect. Though effective, medications can be tricky. If you’re not sure what’s happening with your fish, please contact a fish professional for guidance.

Keep your fish healthy by having the right number of them >>