Anchor Worm on Goldfish? Here We Detail The Treatment For Anchor Worms

Can you imagine an anchor worm crawling under your skin and feeding off your body? It’s not a pleasant thought, so it can be distressing when our beloved goldfish become infected.

Yes, finding an anchor worm on goldfish may be frightening, but it doesn’t have to be a death sentence.

You can rid your goldfish of these nasty parasites so they can get back to enjoying life. Keep reading to find out how.

The Materials You’ll Need To Follow This Tutorial

Here is what to use if you’re treating your aquarium with medication:

Medication Removal

This is generally the most effective method of removing parasites from your tank. It is also less stressful for your goldfish.

Here is what to use if you’re removing the parasites by hand:

Manual Removal

This process is the quickest and produces immediate results, but it can be very stressful for your fish. Proceed with caution.

What Is An Anchor Worm?

Anchor worms, or Lernaea carasii, are a type of parasitic copepod. Copepods are tiny aquatic crustaceans that may or may not live as parasites.

Because Anchor Worms are crustaceans, they are not related to parasitic worms. As crustaceans, they must molt to grow.

Anchor worms are painful because they sink their heads into the muscle of the goldfish. You will most likely find these critters behind the pectoral or dorsal fins.

If the anchor worms infect their host for too long, they will multiply. This is when you will begin noticing the worms all over your fish’s body.

The most painful areas they may infect your fish include the eyes, gills, and fins. Over time, the parasites may burrow into your fish’s internal organs.

It’s likely that the Arrow Worms will cause an ulcer in the area where they burrow. These ulcers can lead to dangerous bacterial infections.

How Do You Know If Your Goldfish Has Anchor Worms?

Anchor worms are visible to the human eye. Still, they are very small, so it’s difficult to catch an infestation in the early stages.

To infect your goldfish, an anchor worm will burrow into the fish’s body. It inserts its body at an angle, usually burrowing between the scales. Their bodies look like small, bony splinters that protrude from your fish’s body.

It’s easier to spot these parasites after the fish’s body has gone into defense mode. As their body tries to fight the parasite, they will begin to lose scales. A blood-red spot will appear around the site of infection. This will illuminate the white, thread-like body protruding from your fish’s body.

Anchor Worms are difficult to spot, but you can catch them early if you pay attention to your fish’s behavior. An infection is itchy and irritating for your fish, so they will try to relieve themselves.

An infected fish will begin darting around their tank. It will rub itself against decorations and vegetation in what we call, “flashing”.

Flashing is usually the first symptom to show up before your fish begins to worsen. As your fish declines, you may notice pale gills, lethargy, rapid breathing, fin clamping, or a lack of appetite.

If these symptoms persist without treatment, your goldfish will only continue to worsen. Eventually, your fish is likely to develop bacterial infections, anemia, and death.

What Makes Your Goldfish Susceptible To Anchor Worms?

Anchor worms are more common if you house your goldfish outside. They appear in the summer months when the temperatures begin to rise. They can appear if an outside water source comes in contact with your pond. This is common with water runoff from a stream or river.

Still, indoor goldfish may experience infection as well. This usually occurs when you introduce a new goldfish to your tank who has an infection.

Step-By-Step Anchor Worm Treatment Instructions For Your Goldfish

Treat Your Goldfish With CyroPro

You can use any fish medication containing cyromazine. But, we find that CyroPro is the most effective.

Cyromazine is an antiparasitic that works great for parasitic copepods. It makes it more difficult for the parasites to maintain their exoskeleton. It also prevents them from developing a new one.

Without their exoskeleton, the copepods will die.

Not only will cyromazine kill the parasites attached to your fish, but it will kill any in your tank.

Step 1: Remove The Filter Media From Your Tank

Whenever treating your tank, you want to remove the filter media but NOT the filter itself. The filter media will remove the medication from the water and render it ineffective.

Remove activated carbon, protein skimmers, and UV sterilization.

Step 2: Perform A Water Change

Before performing this treatment, you’ll want to start with fresh water. Remove 90% of the water from the tank and add in fresh. Be sure to add active bacteria and de-chlorinator to your fresh water.

Step 3: Measure Out The Correct Dose

Be sure to follow the instructions on the bottle for correct dosing. Too little medication will not kill the parasites. Overdosing may kill your fish.

For CyroPro, you will want to measure 1 tsp of the liquid medication per 20 gallons of water.

Be sure to shake the bottle before dosing.

For best distribution, add the medication to the filter box, or pour it around the edges of your aquarium.

Step 4: Continue Treatment

Cyromazine will only affect parasites at certain stages of their life cycle. This means that it won’t kill all the parasites within a few days. You will likely need to continue treatment for a few weeks.

CyroPro recommends redosing every 7 days for a total of 3 weeks. Be sure to complete a 90% water change with each subsequent dosage.

Remove The Anchor Worm Manually

Step 1: Gently Catch Your Fish

Do this quickly, but gently, so as to decrease stress.

Step 2: Remove The Worm With Tweezers

This is the hardest step because it’s difficult and stressful for your fish. Use a pair of tweezers to carefully pull the parasite from your fish’s body. Be sure to remove the entire parasite.

Step 3: Treat The Affected Area With Hydrogen Peroxide

After you’ve removed the parasite, you’ll need to disinfect your fish’s wound. Dip the cotton end of a Q-tip into hydrogen peroxide and gently rub your fish’s affected area.

Step 4: Quarantine Your Goldfish & Clean The Tank

Anchor Worms are incredibly contagious. You should remove your goldfish from its tankmates. Keep your fish in a quarantine tank until you’re sure the infection has passed.

You will also need to thoroughly clean the tank to protect your other goldfish. There may be other Anchor Worms in the water column searching for your other fish.


Have you found this tutorial helpful? We hope that you now have all the information you need to treat your beloved goldfish.

If you notice an Anchor Worm infestation in your goldfish tank, it’s very important to follow these steps. Proper treatment and quick intervention are necessary to save your fish.

If you found this tutorial helpful, consider passing it on. Other goldfish keepers might also find it useful.

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