Anchor Worms On Betta Fish – Treatment & Prevention Guide

    Anchor worms on betta fish

    Anchor worms are not as common for fish keepers to encounter as ich or body fungus. But it’s one of the more dramatic infections you’ll ever see. The worm is often long and a pale white color. What do we do about anchor worms on betta fish?

    Anchor worms can be removed by hand as long as they aren’t attached to sensitive tissues like eyes. The adult worms are resistant to medication but do respond to aquarium salt and potassium permanganate. The free-swimming baby worms respond better to medications.

    Anchor worms have a month-long life cycle so the entire betta tank may need treating. But once you’ve eliminated them for good, its rare for fish to get them a second time!

    What Are Anchor Worms?

    First off, anchor worms are not actually worms at all. They are a crustacean copepod parasite. Many are free swimming and even a source of food for freshwater fish. You can often buy copepods in specialty pet stores.

    Most copepods live on plankton their whole lives. But anchor worms have a parasite life cycle. The section that looks like a worm is really a worm like tail. It is full of eggs that the female creates as she sucks blood from her host.

    The “anchor” is really the head of the animal. It burrows into the flesh and keeps the adult anchor worms from being removed. Adult worms have no separate life from their host. If you remove them, they can’t reattach and will quickly die.

    Here is an excellent video breakdown on what anchor worms are:

    YouTube player

    Where Do Anchor Worms Come From?

    Anchor worms are much more common to see in pond fish than indoor aquarium fish. Outdoor ponds get them from wildlife visiting the water. Frogs can also be infected anchor worms.

    Amphibians, reptiles, and birds sometimes have eggs in their feces. Or on bits of aquatic plants that hitch a ride.

    Wild-caught fish are often loaded with parasites as well, including anchor worms. If you have a specialty import from the wild, the first thing to do is to begin treatment for parasites.

    External parasite infections like gill flukes and anchor worms are easier to see. But wild fish usually have parasites nesting in their internal organs as well.

    Fortunately, once you’ve eliminated parasites from your fish, they tend to stay healthy. Parasites will only find their way back into your tank through new fish or new plants.

    Symptoms Of Anchor Worms On Betta Fish

    Anchor worm symptoms in betta fish

    Fish diseases can sometimes be difficult to identify. But anchor worms are one of the easier ones to ID. They are uncommon in aquarium fish but they do show up. Especially when fish are kept in contaminated water and are overcrowded.

    Symptoms of Betta Fish Anchor Worms:

    • inflamed, red wound on skin
    • visible greenish white or red parasitic worms
    • lethargic behavior
    • scratching against gravel or decorations
    • breathing difficulties

    It is also common for a secondary bacterial infection to erupt thanks to the open wounds. Fish can host multiple anchor worms. The more of them you see on a fish’s skin, the more blood it is continually losing.

    Can Anchor Worms Spread To Other Fish?

    The anchor worm life cycle means that they will spread over time. Even if you manage to eliminate all of the visible worms, the battle has not ended yet. Once the worm has absorbed enough blood, it will release its eggs and then die.

    Many aquarists think that’s all there is to it. Except the juvenile anchor worms will still be around. They live as invisible nauplii in the water column, maturing through several phases.

    Even if you remove visible adult worms from your fish’s skin, a new generation of adult anchor worms will grow up. Without treating the entire tank, you will have infected fish to cure all over again.

    How To Tell If Anchor Worms Are Affecting A Betta Fish

    Once a fish gets anchor worms, its behavior may not change. Heavy parasite loads will cause the fish to scratch against decorations. It may also become weak from blood loss over time. But a single anchor worm will cause it little distress.

    Look out for any of these common symptoms of stress in betta fish. These include stress stripes, lethargic swimming, and clamped fins.

    Can Anchor Worms Kill A Betta Fish?

    A single anchor worm will not kill a betta fish. But several worms on a single fish can kill it from blood loss. Anchor worms are constantly drawing fluids in order to build eggs for the next generation.

    Fish can also die from sepsis, or blood poisoning by bacteria in the infected area. If you have poor water quality, cold temperatures, and other stressors, your betta is even more likely to die from anchor worms.

    How To Treat A Betta Fish With Anchor Worms

    Anchor worm treatment betta

    Anchor worms are resistant to medication once they are visible. But they are not immune to chemical treatments. These are the agents proven to work well!

    Potassium Permanganate

    A solution of potassium permanganate for aquarium fish works very well at killing free swimming anchor worms. Attached worms are hardier but will also be weakened by it.

    Some may be killed by the solution. Especially if you can give them a long-term treatment in a quarantine tank. If you can’t separate the sick fish, you’re better off either removing them by hand. Or you should wait for the worms to complete their life cycle.

    I recommend a dose of 75ml per gallon (25 mg/L). Treat your fish inside a separate bath outside of the main tank for 30 minutes. Or move them to a quarantine tank.

    Potassium permanganate is a strong oxidizing agent. Aquatic plants, fish, invertebrates, and bacteria will be harmed by it if exposed for too long. It is also a dark purple chemical and will stain your water for a few hours if not removed.

    Most aquarium power or canister filters have a satchel or two of activated carbon inside. This is a type of granulated charcoal that does a great job of pulling out organic molecules and chemicals.

    Unfortunately, potassium permanganate is also removed by any activated carbon filter media. Which makes it less effective over time.

    You can turn the filter off for a few hours, if you don’t want to keep the dose going in your aquarium water. If your fish tank is crowded, then it is better to simply remove it. Otherwise, ammonia will accumulate in a crowded community tank with no running filter.

    Aquarium Salt

    Aquarium salt is for more than keeping marine fish alive. It’s also great for exterior parasites like anchor worms.

    Anchor worms are very salt sensitive. The adult phase is hardier but juveniles are killed with constant salt exposure.

    A concentration of one tablespoon per five gallons of water is safe for the majority of aquarium fish. Including salt-sensitive tank mates like tetras, betta fish, and loaches.

    If you have fish that love mineral-rich water, add up to one tablespoon per 3 gallons. Platies, mollies, and cichlids from Central America and the African rift lakes all benefit from you adding aquarium salt.

    Keep salt concentrations stable for 30 days. The life cycle of an anchor worm takes 18-25 days. So you will be able to kill both the adults, eggs, and juveniles in a month.

    Also keep in mind that once you add salt to into your aquarium water evaporation won’t get rid of it. Only water changes remove salt. So when you use fresh water to top off the fish tank, don’t add salt to it.

    Aquarium Salt Dip

    You can do give your betta fish an aquarium salt dip if you’d prefer not to dose your entire tank. Salt dips are great for salt-sensitive species like bettas. The brief bath won’t do anything for anchor worm eggs and larvae that are still in the main tank. But it does weaken the adult worms attached to the betta fish.

    I recommend performing a salt dip at the same time as a potassium permanganate bath. One dip for both medications is better than doing two, which extends the time your betta spends stressed.

    Add enough salt to reach a concentration of four tablespoons per gallon of water. Then add the recommended dose of potassium permanganate (75ml per gallon of water).

    Mix the aquarium water thoroughly. We don’t want any granules of undissolved salt or clumps of permanganate.

    Allow your betta fish to soak in the solution for 30 minutes. Keep a thermometer in the bath solution as well so you can monitor the water temperature. If the water is in danger of cooling below 72°F, use a small heater to keep it in a comfortable range.

    Physical Removal Of Anchor Worms On Betta Fish

    When I worked at a pond store, we had to deal with anchor worms all of the time on goldfish and koi. I’ve removed hundreds in my day. But I would think carefully before pulling an anchor worm from a betta fish.

    The problem is that the worm is massive compared to the betta fish. The worm has a root-like “anchor” that pulls a small piece of flesh out when you remove it.

    That’s painful and annoying for a goldfish or a koi. But a betta fish is so small that you could do a lot of damage to it. If your betta has a single anchor worm and it’s not too long, it’s worth the risk.

    But a large anchor worm – or several anchor worms – should not be removed by hand. The betta fish might end up bleeding out. Or the wounds become infected, killing it.

    How to Remove Anchor Worms by Hand

    Only remove anchor worms if they are attached to less delicate tissues. If they are attached to the eyes, gills, mouth, or other sensitive structures, do not try to remove them by hand. You will cause major damage and possibly kill your fish.

    To remove anchor worms, you need to catch the infected fish in a net. Wet your hands as well. Never touch a fish with dry hands as it will strip away their protective slime coat.

    With a pair of tweezers, grasp the worm firmly at the base where the stalk meets the fish’s skin. Copepods are crustaceans and have a hard outer exoskeleton. They don’t crush easily so get a good grip.

    Pull upwards, while keeping a good grip on your fish with your other hand. The fish will thrash as this is painful. You will uproot the parasitic infection entirely this way.

    Place the fish back into your aquarium. And treat the tank with a light dose of aquarium salt and a healing antibacterial agent. I prefer Melafix since the tea tree oil it contains also helps wounds recover.

    Treating a recovering fish in separate quarantine tank is better than adding it to your main aquarium. A quarantine tank allows the fish to eat without having to compete for food with healthy fish.

    You can also use medications that may be toxic to sensitive pets like shrimp and snails.

    Perform Water Changes

    Large water changes are another way of “physically removing” anchor worms. In this case, you’re sucking up any eggs and free swimming juveniles that are living in the tank.

    I’d start with a 50% water change. Though if you have time a 100% water change will eliminate all anchor worm eggs and larvae.

    I would only do a complete 100% water change if you have a single betta fish living alone. You are partially resetting the aquarium nitrogen cycle by removing all of the water.

    This can lead to new tank syndrome, where ammonia produced by fish is no longer being processed effectively. That said, if you preserve your old filter media, the beneficial bacteria living inside of it will still process ammonia as normal.

    Also get a handle on any issues with poor water quality. Anchor worms are not caused by dirty water. But ammonia, nitrite, and nitrate cause added stress. Keeping the tank clean helps freshwater fish recover from diseases faster.

    How To Prevent Anchor Worms On Betta Fish In The First Place

    If you can prevent parasites from finding their way into your fish tank, you can keep fish healthy with less effort!

    Examine New Fish Thoroughly

    The first and best strategy is to notice anchor worms before you buy a new fish. They are very obvious since they cause wounds and have a long, trailing tail.

    A single worm, hidden inside of a gill might escape notice. But you should never choose a new fish just because it’s pretty or the right kind. Always look for spots, worms, and other signs of poor health.

    Is that colorful betta fish swimming with difficulty? Or does it have frayed fins or labored breathing? If so, then pass on it. Don’t expect to be able to nurse it back to good health.

    Another use for a quarantine tank is for literally quarantining plants and fish that arrive home. The best aquarium stores have their own quarantine process. Distributors often send merchandise full of snails, bacteria, and parasites.

    But with less diligent retail shops, give yourself one week to examine a new fish. Especially an expensive fish. It may have no visible anchor worms when you buy it. But then develop them after it arrives in your main tank.

    Keep Pet Store Water Out Of Your Fish Tanks

    When you buy a new fish or plant, it comes in a small plastic bag full of water from your pet store. Most aquarists take their purchase home and float it for 15 minutes so the temperatures equalize. And then they release the fish along with all that water.

    You should never, ever dump pet store water into your tank. It is almost always full of parasites like ich, anchor worms, velvet, fungi, and bacteria.

    Even in the cleaner aquarium specialist stores, this is true. Their tanks are almost always overstocked, giving germs and parasites plenty of hosts to choose from. They are also getting fish and water from distributors. Who might not be very diligent about providing clean conditions since their aquarium stock is always moving.

    Remember, juvenile anchor worms are free swimming and invisible to the naked eye. They can find their way into your fish tank through pet store water.

    Are Anchor Worms Contagious To Humans?

    You’ve nothing to worry about from an anchor worm infestation. They are aquatic organisms and can’t survive outside of the water. Most parasites are also very selective in what they can infect.

    They will parasitize just one group, as anchor worms do on fish. Or they will infect just one genus, or even a single species. Some parasites do have a life cycle where they may infect one host as a larvae. But then jump to another as an adult.

    But anchor worms are planktonic animals as juveniles. They can’t live out of the water and they certainly cannot infect humans!


    Anchor worms are not the most common betta diseases around. But they are one of the more dangerous types. The worms can cause damage or death to a betta fish if removed from a sensitive location. And they resist many medications.

    But with the right medicines and future prevention, you should never have to deal with them again!

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