Camallanus Worms in Aquarium Fish: Causes and Treatment

Camallanus worms pose a serious threat to aquarium fish, impacting a variety of species. This comprehensive guide takes you through the causes, symptoms, and key prevention strategies of this parasite. Understand the lifecycle of Camallanus worms and learn effective treatments to safeguard your aquarium fish.

camallanus worms in fish

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What are the Causes of Camallanus in Fish?

The primary cause of Camallanus in fish is the consumption of infected hosts. Tiny creatures that carry the infective larvae of Camallanus such as daphnia, tubifex worms, or other small crustaceans unknowingly enter aquarium ecosystems, often through live food or new plants.

Ingesting fecal matter from already infected fish is another way the worm can spread. It’s important to note that the larvae can survive for quite some time, waiting to be ingested. This allows the possibility of infection through contaminated water or objects as well.

In short, here’s the summary of the causes:

  • Unsanitary live food sources.
  • New organisms or objects introduced without proper quarantine.
  • Contaminated water and fecal matter from infected fish.

Remember, prevention is better than cure. Take particular care when introducing new items into your aquarium, quarantine if you can, and make sure the food you’re using is from a reputable source.

What Fish Species Are Susceptible to Camallanus?

Research has shown that Camallanus worms are not picky eaters. They affect a vast range of aquarium fish species, whether exotic or commonplace.

camallanus worms in angelfish

Oscarsdiscusangelfish, and guppies are among the well-documented vulnerable tropical fish species. Moreover, koi and goldfish are not exempt either, showing signs of infection in several cases. Predatory fish are particularly prone to an attack due to their meat-eating habits.

Many other species can fall prey to these parasites. However, susceptibility can vary with factors like water quality, diet, or stress levels. Therefore, it isn’t certain that all individuals of a species will invariably be affected.

Far from being confined to one or two types, the threat of Camallanus extends to numerous species. This fact reiterates the importance of keenly observing your fish and taking precautions to avoid any worm infestation. Suffice it to say, any fish species in an aquarium setting can potentially become the host to these unwelcome guests.

What are the Main Symptoms of Camallanus?

Recognising the symptoms of Camallanus in fish is vital in ensuring their well-being. As a fish owner, you need to be proactive and observant in monitoring your aquatic pals.

  • Visibility of Worms: This is probably the most telltale sign. The worms will reveal themselves, rearing their bright red, spaghetti-like bodies from the anus of your fish.
  • Lethargic Behaviour: Infected fish might swim noticeably less, show outstandingly low energy and enthusiasm.
  • Loss of Appetite: Pay attention if your fish starts refusing meals. This can indicate the presence of these parasites.
  • Rapid Weight Loss: Despite regular feeding, your fish might suffer from significant weight loss, looking extraordinarily thin and frail.
  • Dull or Losing Colour: Fish might lose their vibrant colours, appearing dull, which is another sign of being infected.

Always remember, these symptoms might not appear in the early stages of the infection, but late manifestation doesn’t mean absence of infection. Be attentive, stay prepared. Prevention is always better, but if your fish show any of these symptoms, quick treatment can save their lives.

How Does Camallanus Transmit to Other Fish?

Camallanus worms, known to be deadly parasites, have quite a unique and intricate life cycle that assists their transmission between fish. The underlying factor is the fecal-oral route, showcased in three main processes.

dead guppy fish with camallanus worms

Firstly, the adult worms within the infected fish produce larvae, which are excreted in fish feces. When these droppings settle onto the substrate in your tank, they become food for microorganisms, turning into a perfect delivery package for the larvae. Here’s the cycle in a nutshell:

  • Infected fish passes larvae in feces 
  • Fecal matter serves as food for microorganisms


  • Microorganism containing larvae are consumed by other fish


  • Larvae develop into adult worms in new hosts

Secondly, the larvae need to undergo development within an intermediate host, usually a small crustacean, before they can infect other fish. Fish that consume such contaminated crustaceans unknowingly ingest the worms, which then grow to adulthood within their intestines. This presents a high risk, especially if you often introduce live food to your aquarium.

Lastly, Camallanus can be directly transferred from one fish to another when they nibble or consume dead bodies of fish that were infected.

This is how Camallanus expertly exploits the biological and behavioral traits of fish in their cycle of transmission. It also emphasizes why careful observation and control of feeding habits in your aquarium is crucial in keeping Camallanus at bay. 

What are the Prevention and Treatment Options for Camallanus?

When it comes to dealing with Camallanus worms, an ounce of prevention is worth a pound of cure. Implementing a robust quarantine protocol is the first line of defense against this notorious parasite.

  • Isolate new fish: Always quarantine new fish for at least 4 weeks (1 month). During this time, carefully watch for signs of Camallanus or any other diseases.
  • Disinfect everything: Regularly clean and disinfect all tools, nets, and equipment. Even decorations or substrate taken from infected tanks can carry the parasite.

If, despite all your efforts, Camallanus takes hold in your tank, it’s time to turn to treatment options. Unfortunately, Camallanus is notorious for its drug resistance, but there are still a couple treatments that may be effective.

  • Levamisole: This is the most common and often the most effective treatment. Administer levamisole at a dose of 2 g/100 liters (~25 gallons) of aquarium water.
  • Fenbendazole: If levamisole doesn’t eliminate the infestation, fenbendazole may be effective. Use fenbendazole at a dose of 2 mg/liter (~8 mg/gallon) of aquarium water.

During treatment, be vigilant about water quality. Remember to renew at least 25% of the water weekly and all after treatment. Then, repeat the treatment after a couple weeks to ensure you hit any newly hatched worms. But remember, it’s always better to avoid the infestation in the first place!

How to Treat Camallanus Worms with Levamisole?

Camallanus worms in aquarium fish can be a dreadful sight for any hobbyist. These parasitic worms are not only harmful to your aquatic pets but can disrupt the entire ecosystem in your tank.

Levamisole, an anti-worm agent, is an effective treatment for this infestation. Here’s a step-by-step guide to help you treat your pets:

  1. Determine the dosage: Usually, a dose equivalent to 2 ppm (2 grams / 100 liters) is sufficient for levamisole-based treatments. Remember, adding extra will strain your fish, not treat them.
  2. Administer the dose: Add the correctly measured treatment to your aquarium, ideally when you can monitor the fish for a few hours. Expect most of the worms to be released within the first 24 hours.
  3. Keep the tank clean: It’s essential to vacuum the tank to extract the paralyzed worms. Prolonged exposure can turn these parasites into food for the fish, restarting the entire infestation cycle.
  4. Wait before the water change: Resist the urge to change the water immediately. The medicine needs a full three days to be absorbed by the fish. A 25-30% water change on the third day will be just right.
  5. Repeat as needed: Do another round of treatment after two weeks to ensure any hatched eggs are also eradicated. For a well-rounded attack on these parasites, repeat this step one more time.

Remember, levamisole is potent but neutral in varying PH levels. While it’s highly effective against camallanus worms, it can be harmful to shrimps, snails, and certain delicate fish. It’s best to seek a vet’s advice before taking any drastic steps.

What is the Lifecycle of the Camallanus Worm?

Understanding the lifecycle of the Camallanus worm helps in prevention as well as treatment. The lifecycle of Camallanus can be divided into two distinct stages: an internal stage and an external stage.

During the internal stage, adult female Camallanus worms lay eggs in the intestines of infected fish. These eggs then exit the host fish during excretions. The eggs hatch into larvae while still in the excrement and fresh water.

camallanus worms in guppy fish

This kicks off the external stage of development. Here are the main steps:

  • The larvae molt in water and turn into first-stage larvae.
  • After a series of molts, they become free-swimming third-stage larvae.
  • These larvae are ingested by intermediate hosts, usually small crustaceans like copepods.
  • Inside these hosts, the larvae develop into invasive fourth-stage larvae.
  • If the infected crustacean becomes a meal for a larger fish, the process repeats.

This cyclical pattern is what allows Camallanus worms to spread and infest entire aquariums over time. This understanding can guide you in choosing the right measures to break the cycle and control the infection in your aquarium.

How Does Camallanus Affect Aquarium Fish?

Camallanus worms have a significant impact on your fish’s health. These parasites can disrupt the normal digestion and absorption of nutrients in your fish, leading to a reduced appetite and slow growth rate.

Once they’ve infested the intestinal tract, Camallanus worms cause physical damage. This can induce internal bleeding and other visible signs such as redness and swelling of the affected area.

Not only do these worms degrade the health of your fish, but they also alter their behaviour. Infected fish might isolate themselves, lose interest in food, or swim erratically.

Remember, Camallanus worms are notorious for their resilience. They have a thick outer layer that can withstand a wide range of temperatures and pH levels. Even in adverse conditions, these worms can continue their harmful activities inside the host fish.

Here’s a glimpse of the worm’s impact:

Impact Symptoms
Physical Reduced appetite, slow growth, internal bleeding, redness, swelling
Behavioural Isolation, disinterest in food, erratic swimming

Preventive measures are essential because once the Camallanus worm starts damaging the fish, it becomes tough to reverse the condition. The key is to detect and address the problem early on.

What are the Best Methods for Diagnosing Camallanus?

Identifying a camallanus infection early is crucial for successful treatment and prevention of further spread. The most reliable way to diagnose camallanus is through observation of physical symptoms in your aquarium fish.

guppy fish infested with camallanus worms

  • First and foremost, look for red or pink “threads” hanging from the anus of your fish. This is the most common symptom and a strong indicator of camallanus.
  • Secondly, observe your fish’s behavior. Infected fish often appear lethargic, may lose their appetite, or exhibit unusual swimming patterns.

In addition to visual inspection, a fecal examination is another method to diagnose camallanus. This involves examining a sample of the fish’s feces under a microscope, looking for larval stages of the worm. Be aware, however, that this method may not be foolproof due to the worm’s complex lifecycle stages.

Lastly, when fish die without clear causes, a post-mortem examination, or necropsy, can provide definitive diagnosis. This is usually performed by a veterinary pathologist who can accurately identify the parasite.

When diagnosing camallanus, remember that early detection is key. Keep a close eye on your fish and their behavior, and take action at the first sign of trouble. Remember, prevention is always better than cure.

Is Camallanus Contagious to Humans?

In the realm of aquarium maintenance and aquaculture, the concern for the zoonotic potential of diseases is quite prominent. Let’s cut straight to the chase – are Camallanus worms contagious to humans?

The answer is No. Camallanus worms aren’t typically a risk to human health. These parasites are species-specific, implying that they prefer to infest certain species of fish and don’t naturally infect or harm humans.

Though a relief, this doesn’t rule out the possibility of incidental infections. Accidental ingestion or improper handling of infested fish might cause complications. But remember, such instances are extremely rare.

Practically speaking, Camallanus worms pose more threat to your aquarium fish than to you. Also, just as a precaution, always wash hands thoroughly after handling any aquarium, regardless of whether it’s infected or not. Thus, for the average aquarist maintaining good hygiene, the worry about Camallanus worms isn’t about personal health.

Their effect is more likely to be seen in the health of your aquarium ecosystem. By focusing your efforts on keeping the tanks clean and the fish healthy, you prevent the spread of the Camallanus amongst your fish.

In the end, though it may seem like a grim topic, understanding the risks (or the lack of them) posed by these worms will only help you better manage your aquarium.

FAQs about Camallanus Worms

IN the following we should effectively address some of the common questions you might have had about this pest. Prevention and timely reaction are crucial to controlling the spread of Camallanus worms.

Can I see Camallanus worms with the naked eye?

Yes, indeed. Camallanus worms are visible to the naked eye as they stick out of your fish’s anus.

How fast do these worms spread in aquariums?

Quite speedily, unfortunately. In just a fortnight (two weeks), they can infest your entire tank.

Is there a specific season when Camallanus worms are more common?

There isn’t. These resilient worms can occur and breed at any time of the year.

Can these worms harm humans?

The answer is no, fortunately. Humans are not suitable hosts for these worms, so you are safe.

Can I prevent Camallanus worms?

Absolutely. Good hygiene, regular maintenance, and using food from trustworthy sources can prevent them.

Is there a curative treatment for infected fish?

Yes, for sure. Medications such as Levamisole and Fenbendazole are effective against Camallanus.

Can these worms survive outside the fish tank?

Unfortunately, yes. Camallanus worms can survive in moist conditions outside the tank for up to a week.

How often should I clean my aquarium to prevent these worms?

Regular cleaning, as often as once a week, is highly recommended. Cleanliness is deterrent to these pests.

How severe are these worms to the fish’s health?

Quite severe, tragically. Camallanus can cause inflammation, destruction of the fish tissue, and even death.


While it’s clear that Camallanus worms can be disastrous for your aquarium fish, you can still tackle them through vigilance and proper care. Don’t forget, prevention is always better than cure.

Please feel free to leave a comment if you found this guide helpful or if you have any personal experiences to share.

Questions and Answers

Michelle Barringer March 18, 2020 Reply

Hello Fabian,
I thoroughly enjoyed your article on the camallanus worms.
I’m so frustrated and discouraged!! I have a 20 gallon long aquarium that houses guppies, mystery, malaysian & rabbit snails as well as Neocaridina shrimp. All snails and shrimp are thriving!
Sometime ago I traded some fish and apparently brought in the nasty, disgusting worms. I treated with API General Cure and I actually saw worms being expelled from the poor fish. After a few months the worms are back…. I’m losing guppies. Here’s my question, I bought a 5 gallon tank for quarantine. 1)Do you think I should move all of the guppies to that tank, keep it bare, and treat with levamisole? 2)Can the guppies ever go back into the 20 gal. tank? Will they just continue to be re-infected? Any suggestions would be greatly appreciated!

Thank you in advance for your time!!

    Hello Michelle!
    Cacallanus worms are really nasty. I had a camallanus problem in few of my tanks and pretty much wiped out half of fish population from those tanks.
    Usually, it takes about 3-4 weeks for camallanus worms to die off in an aquarium, if there is no fish present, but I’m not 100% sure about this, because I had the same problem as you – the worms are keep coming back.
    Finally, I did a restart to the infested aquariums, and treated the fish separately. Unfortunately, some of them died in the process.
    Keep in mind, that you need to disinfect the equipment, substrate and filter media as well. If you have plants, you need to treat the plants as well.
    Also keep in mind, that the medication used to kill camallanus worms, can also kill shrimp and snails. So if you have a community tank with snails, shrimp and fish, it gets really hard to get rid of camallanus worms.

Hi I have just treated a Bolivian ram showing calamanus worms at the anus. I used levamisole and followed the directions which said do 50% water change after 24 hrs. She expelled the visible worms within the 24 hr period and even regain d some of her colour and started swimming again on and off but now she is at the back off the tank again and not eating. Did I do the water change too quickly or have I just started the treatment too late

    Each fish can react differently to the treatment. From experience, I found, that fish that have the worms sticking out from their anus are already in really bad shape. Some of them can recover, but most of them will die.
    I don’t think you did the water change too quickly, it really depends on how bad your fish is infested. Also take in consideration, that camallanus worms are really hard to get rid of. Even though your fish got rid of the worm that was visible, it is possible that there are still worms in its guts. One treatment will not get rid of the worms, it can take up to 3-4 weeks to completely eliminate this nasty parasite from your aquarium.

Thankyou very much for your quick reply I have been trying to research this for days to do the right thing do I have to wait the 2 weeks to treat her again. I used eSHa- ndx which was one drop per litre or would it be worth trying a bacterial treatment in between

Robert Baker April 20, 2020 Reply

I have been dealing with Camallanus for several years now. I could not find out what to do and finally I found a University that had an aquaculture lab. Bingo,I had those nasty nemotodes. This too shall pass bit it is nasty!

I’ve removed my infected guppies and place them in a quarantine tank for treatment. My 30g has no other occupants, just snails and plants. After treatment when will my main tank be safe to house fish again? Thanks 🙂

    I’ve did a lot of research on this topic, and in theory, camallanus worms should be gone after 3-4 weeks if there is not host for them (fish). I’m not 100% sure if this is true, because I’ve had cases when the worms came back. Maybe it was an infested tool, or a drop of water from another aquarium, I don’t know. It is pretty hard to get rid of them, that is for sure.

    Probably there a high dose of salt will kill camallanus worms, but it will also kill your fish. Using a safe medication is much better and safer than overdose of salt. I know that these medications are expensive, but I found to be the only way to get rid of these worms.

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