Parasites that Affect Koi and Goldfish
 

Parasite infestation is one of the most common afflictions that can happen to koi and goldfish in our ornamental ponds.  Most parasites, by themselves, are not particularly deadly but they set the stage for bigger and worse things to come.  When koi and goldfish have parasites two things will happen.  The parasites will aggravate them and cause them stress.  Stress for fish is a killer.  When stressed they have low tolerance to disease.  The second thing that can happen is the parasite can cause damage to the skin of the fish.  This allows bad bacteria to invade the flesh and cause bacterial infections such as ulcer disease.  Some, such as gill flukes, even carry bad bacteria and, for all practical purposes, inject the bacteria into the flesh.

Only a few of the parasites known to attack koi and goldfish are large enough to see with the naked eye.  Those parasites are argulus, anchor worm and ich when its in advanced stages.  Often people will tell us that their koi and goldfish do not have parasites because they can't see them.  We have to, at that point, correct them.  Most parasites cannot be seen unless you look at them under a microscope.  It's rather simple to do a biopsy using a microscope to identify if and what kind of parasite is present in the pond.  If interested, please visit The Pond Doc's Online Office to find out how to do it.

Each parasite has its differences but they all share certain things.  They all can kill (or aid in the killing of) our koi and goldfish.  They all can be transmitted by new arrivals who have not been quarantined and treated.  They all need fish hosts in order to survive.  They all can be easily eradicated from the pond. 

If one fish has parasites - they all do.  The whole pond has to be treated.  Plants can also bring in parasites if they are stored in tanks or ponds with fish.  It's true that parasites cannot last very long without having a fish host but they can certainly survive the trip home.  For that reason it's smart to treat plants before placing them into your pond.  

.The Symptoms of Parasites

So how do you know if your koi and goldfish have parasites?  If you do not have the benefit of a microscope you really don't know for sure if your fish have them and, sometimes more importantly, which parasite they have.  Most of us cannot easily do a biopsy to pinpoint which of the parasites are present so we must depend on the behavior of the fish, any other complications that may pop up and common sense. 

If the koi and goldfish are scraping themselves on the bottom or sides of the pond (called "flashing") that's one of the best indicators.  They are simply trying to scratch an itch!  Parasites tickle them.  Sometimes they'll take leaps out of the water to try to calm the itching.  Head hanging is another behavior that might spell parasite infestation.  Gill flukes attack the gills of the fish so if the fish is gasping for air and scratching itself it may be flukes causing it.  New fish are notorious for bringing in unwanted guests. 

Use your common sense.  If it's been a couple of weeks since you added new fish to your pond and they have begun acting "strangely" and looking sick, flashing and/or gulping air chances are your new fish brought parasites with them.  In fact, I would go as far to say that 99% of the fish you bring home will have some sort of parasite. 

Treating for Parasites

Unfortunately, there is no ONE treatment that will get rid of all the different parasites because what works for one will not work for the other.  If you have the luxury of being able to do a biopsy and know exactly which parasite(s) are present you can look at that parasite's page (links are on the right) to find out which of the two methods will work for your pond. 

If you don't have any way of knowing which parasite it could be then you will need to treat with both methods.  It doesn't matter which one you do first (unless maybe you suspect one kind) but it's important that you do the treatments one after the other - NOT AT THE SAME TIME.  We have made it easy for you by creating a "Parasite Pak" that includes both types of treatments and the directions to use them.

Click on the red cross to find a Parasite Pak at our Fish Pharmacy.

Preventing Parasitic Infestation

There's a sure-fire way to insure that you do not bring parasites into your pond and that is to quarantine and treat them.  We can't say that enough!  If you have no way to quarantine and treat them then what we suggest to do is go ahead and assume that any fish you place into your pond will have parasites.  After you add all the fish you are going to add for a while treat the pond with a parasite pak to insure you get any that could be present. 

For more information about quarantining and how you can prevent parasites from invading your pond visit the Pond Doc's School of Preventive Koi Care.

More Information About Parasites

• Flash Dance - A Closer Look at Parasites

Parasites

Anchor Worm

Argulus (Fish Lice)

Chilodonella

Costia

Gill Flukes

Ich

Trichodina

© copyright, 2008, PondDoc.com.  Reproduction or use of any content on this website prohibited without written consent from PondDoc.com.  This advice is given free of charge and serves as information only to help you with determining the cause of fish health problems.  The content given is to be used as guidelines only.  By following the guidelines on our website you are agreeing that we will not be held responsible or liable for any losses.  We cannot diagnose your specific case.  We are simply forwarding the benefit of our extensive experience with koi and goldfish health.