The Anchor Worm Treatment Guide

Anchor worms are a nasty parasite from the Lernaea species that embed their anchor-shaped heads into the scales and flesh of your fish. You can tell you’re dealing with them when your fish have 25mm white, stringy specimens hanging off of their bodies.

If what I’m saying sounds familiar to you and you think you’ve got a case of anchor worms on your hands, luckily, you’ve come to the right place. To start this article, we’ll explain the life cycle of anchor worms. Then we’ll get into which steps we recommend taking to perform proper anchor worm treatment. By the end of this article, you should be equipped with everything you need and need to know to treat anchor worms as well as preventing them from ever wreaking havoc in your main aquarium again.

Anchor Worm Life Cycle

After adult anchor worms mate, the male dies off and the female embeds her anchor-shaped head into the scales of the host fish. After about 24 hours, she’ll release her batch of about 250 eggs into the water column. Each of these eggs hatches within 24-36 hours and begin free-swimming in your aquarium, in the hunt for its host (one of your fish). Right when they find their host, they don’t embed themselves right away. Instead, they kind of just hang out on the surface of their bodies until they find a mate. Once they do, the process just repeats itself.

The entire life cycle from egg to mature adults takes anchor worms about 18-21 days. And once the females are producing eggs, they typically release a new batch into the water column every 2 weeks or so. It forms a real problem.

How to Get Rid of Anchor Worms

There are actually several different ways that you can treat anchor worms, but the general idea is to remove the adult females that embed themselves into your fish, and halt the growth of the rest of the specimens that are in the pre-adult stages. If you were to only remove the embedded females, you’ll find yourself in a vicious circle of yanking them out of your fish every week or so because the eggs and larvae will continue to mature, reproduce, and embed themselves into your fish. So to stop the life cycle from continuing, you’ve got to eliminate the adults, eggs, the free-swimming larvae, and the specimens that are on the bodies of your fish but have yet to embed themselves.

So without further ado…

Step 1

Do a Water Change

No matter what kind of disease or infection you are dealing with in the fishkeeping hobby, it’s always a wise decision to start your treatment efforts with a water change. By doing so, you’ll ensure that your aquarium water is in good condition for your fish to heal in. The last thing you’ll want to do after removing the anchor worms from their body is place them–covered with open wounds–into an aquarium with toxic water parameters.

The second benefit you’ll see, specifically in relation to anchor worms, is that while you’re siphoning out some water, you’ll most likely siphon out a good chunk of anchor worm eggs and free-swimming juveniles.

Step 2

Remove Any Carbon Media for Your Filter

As handy as carbon is for removing odors and tannins (the stuff that makes your aquarium water turn a yellowish tinge), it also removes any medication that you put in your aquarium. Since we’ll need to add some to properly treat your anchor worms problem, go ahead and remove it for now. You can add it back after the process is over.

Step 3

Bath the Fish in Potassium Permanganate

Placing all the fish from your aquarium in a bath of Potassium Permanganate will kill any immature anchor worms that are on your fish but have yet to embed themselves, however, it may not kill the ones that have. Either way, it’s effective and a good place to start.

The substance is actually in a powder form out of the bottle, so you’ll need to mix it a bucket that has aquarium water. Once it’s dissolved, it should be safe for you to add your fish to the bucket.

Ideally, the bath should last 30 minutes and have a concentration of 25 mg/L in the bucket.

Step 4

Remove Any Embedded Anchor Worms

At this point, it’s a good idea to transfer your fish from the bucket filled with the Potassium Permanganate into a separate bucket, filled only with aquarium water. When you’ve got your setup ready to go, grab a pair of tweezers in one hand, one of your fish in the other (wearing aquarium gloves, of course), and prepare yourself. What you’re going to want to do is firmly hold your fish near the infected area, grab the anchor worm as close as you can to the base of it with the tweezers, and quickly pull it out.

After you’ve pulled it out, discard of the anchor worm, and repeat the process until your fish is free from all of them. If your fish has quite a few, it’s probably a good idea to dip him back in the bucket of water for a few seconds so he can catch his breath. Once they are all removed from the fish though, you can place him back into the aquarium and grab the next in line.

Step 5

Treat Your Aquarium with Dimilin

Dimilin is a medication that disrupts the growth of anchor worms, kills any adults that haven’t embedded themselves into a fish yet, and kills any larvae. As per the manufacturer’s instructions, to properly use Dimilin for anchor worms, use one tsp per 500 gallons of water in the aquarium. Use the calculator below if you need a hand figuring out how much to add for your size of aquarium.

Aquarium size:

Not sure?


You should mix tsp into some aquarium water and pour % of that mixture into your tank.

The important thing to note with Dimilin is that it doesn’t kill the anchor worms that are in egg form. So to be effective, add another dose after 3-5 days to kill any larvae that were eggs during the previous dosing. You can do this as many times as you need to until the problem is solved, but don’t exceed more than 3 doses per month.

Step 6

Treat Your Aquarium with Aquarium Salt

An anchor worm salt treatment has been found to be very effective. As a matter of fact, a study found that anchor worm eggs wouldn’t develop into adults if their water had a salinity of 4.8 g/L. With this knowledge and knowing the anchor worm life cycle spans 18-25 days, achieving a salinity of 4.8 g/L in your aquarium for about 30 days should in theory eliminate the possibility of anchor worms surviving in your aquarium.

Now before you go rushing into things and dumping aquarium salt into your tank, we recommend researching your specific species of fish. Some fish can’t survive at such a high salinity level. So for the sake of your fish, please do some research.

If you’ve found that your species of fish is hardy enough to withstand the salinity, use this calculator to determine how much you need to mix into your aquarium to achieve a 4.8 g/L (or 4.8 ppt) concentration. And, as always, remember to dissolve your aquarium salt in some aquarium water before adding it to your tank. But don’t add it all in one go. As a general rule of thumb, adding many small doses of salt is healthier than adding one large dose of salt.

Step 7

Monitor Your Fish

Anytime your fish have open wounds on their body, they are susceptible to secondary infections. During their recovery time, be sure to keep a close eye on them. If you notice anything suspicious with anyone in particular, it may be best to transfer them to a hospital aquarium where they can recover in peace.

It’s also a really good idea to keep up with constant water changes. If your water parameters turn toxic on your fish, and they are battling recovery already, you’re not really setting them up for success. After each water change, it would be a good idea to replace any aquarium salt that you’ve removed during the process. Use the same calculator as before and as you replace water during the water change, add enough aquarium salt to the new water so that it has the same salinity as the water in the aquarium (4.8 ppt).

Once your tank doesn’t have any more anchor worms, larvae, or eggs, you can stop adding aquarium salt during your water changes.

Preventing Anchor Worms

Anchor worms can only enter your aquarium when you add a new, but infected, fish into your tank. As such, the only ways to truly prevent an infestation is to:

  1. Only purchase your fish from reputable dealers, breeders, and fish stores.
  2. Always quarantine any new fish you get for about 1 to 2 weeks before adding them to your main tank.

By placing any new fish into a quarantine tank, you’re able to observe its behaviours. If anything seems suspicious, or you see any signs of disease or anchor worms, it’s easiest to deal with the problem at that point instead of after it infects your main tank.


Anchor worm treatment is rather straightforward. Just follow the steps outlined in this article and you should be on the right path to success. After you have gotten rid of the nasty parasite, observe the gem of wisdom that you’ve had land on your lap: Always quarantine any new fish before adding them to your aquarium.

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