The name “anchorworm” is actually a misnomer of sorts because the “worm” isn’t a worm at all – the parasite is a small crustacean, not an insect, which is usually relatively rare with tropical aquarium fish because it prefers cooler water.
Typically, anchor worms are only seen in pond fish and recently wild caught specimens – goldfish are another frequent victim of this pesky crustacean. You can also inadvertently introduce anchorworms, both eggs and in their free-swimming stage, by adding live plants to your tank or feeding your puffer live foods.
However, since the majority of freshwater puffers are wild caught fish, you may end up having to deal with an infestation of anchor worms at some point – our Red Congo Puffer (Tetraodon miurus) came home with one that emerged near its gill, in addition to a few other problems, like constipation, fish ick and a few bite marks.
What do anchor worms look like?
The first time that I saw an anchorworm on a fish, I thought that it had a piece of food sticking out of its gill – when the adult form of the parasite is attached to the fish it looks like a small stick with a forked tail.
The anchor worms that attach to your puffer are female, and they carry their egg sacs at the end of their body where the fork is located – the sacs are long and shaped like a tube; however, without a microscope they have the appearance of little balls because they are normally twisted or rolled up.
As their name implies, the head is shaped like an anchor, which makes it so that the parasite can attach firmly to your fish – this is necessary because the afflicted fish will often rub against rocks and other objects in an effort to dislodge the anchorworm. There are different types of anchorworms – they can be found on the eyes, skin, and gills of fish, sometimes burrowing deeply into the musculature to anchor themselves on their host.
Depending on the species, anchorworms can be white, green, red, grey or brown. Sometimes, the females attached to your puffer may appear threadlike, lacking the forked body, because they are immature – they will develop the Y shape when they mature and produce egg sacs.
What symptoms will my puffer exhibit if it has anchor worms?
If you just purchased a wild caught puffer, then you may see anchor worms crop up in a couple of weeks.
A puffer infested with anchorworms will exhibit one or more of the following:
- Loss of appetite
- Dull coloration/darkened belly
- Swollen bumps on the skin
- Difficulty breathing (from anchorworms in gills)
- Unexplained puncture wounds
- Obvious anchorworms hanging out of the body
Sometimes, a swollen bump will form where the anchorworm is attached to your puffer – this can become red and infected, so it’s very important to keep an eye on the site.
What is the life cycle of an anchor worm?
Like fish ick, anchor worms have a free swimming larval stage, as well as an adult stage where they are attached to the body of the fish.
The larval stage burrows into the muscle of the fish to develop, and will only emerge from the skin when it’s an adult – as the anchor worm is burrowing back out of the skin, you will probably notice your puffer flashing and rubbing up against objects in an attempt to get rid of the irritation.
The free swimming larval stage can be introduced through contaminated water, as well – which is why you should never add the bag water to your main tank.
It takes the larvae several months to develop, emerge and then mate – once the female anchorworm attaches to the puffer, it will take a couple of weeks for the eggs to develop and hatch. When the eggs hatch, you will have a fresh batch of microscopic anchorworms swimming around in the water column searching for a host so that they can repeat the cycle again.
Can anchor worms kill my freshwater puffer fish?
Yes and no – if your puffer dies after being infested with anchor worms it will probably be because of a secondary infection or an overdose of medication. Technically speaking, a heavy enough infestation could definitely kill a fish – but it would most likely be the result of weakened state of the puffer caused by the feeding habits of the attached anchorworms.
When an adult female anchor worm burrows underneath the skin of your puffer, completes its life cycle by laying eggs, and then dies, the parasite will leave an open wound. This leaves your puffer susceptible to secondary infections, which can be difficult to treat because puffers are scaleless fish – in conjunction with the fish’s weakened state, medication can sometimes prove fatal.
How do I treat a freshwater puffer with anchor worms?
There are three different methods of getting rid of anchor worms:
- Using medicine dips
- Dosing the entire tank
- Applying medicine directly to the anchor worm
The most common remedy for pufferfish with anchorworms is a medicine called Praziquantel. Although Prazi can be injected into food items, like snails and night crawlers, to treat internal parasites, I opt for treating the entire puffer tank because unlike IP’s, anchorworms have a free swimming stage – if you only dose the food with medication, you will not eliminate any of the larvae before they reach your puffer to repeat the cycle.
If you’re having difficulty finding a pet store that carries Prazi, then you can always look online, as well – I buy the Jungle Parasite Clear Tank Buddies (fizzy tabs), which contain Praziquantel. You can treat 10 gallons with each tab, so a 30 gallon tank will need approximately 3 tabs per dose. You will want to dissolve the tabs before adding the medicine to the water.
I also follow up treatment for anchorworms with a dose of Melafix to help prevent the wounds left by the dead parasites from becoming infected – Melafix is widely accepted as a gentle enough medication to use on puffer fish, just remember to increase the amount of dissolved oxygen during treatment as a safety precaution.
In addition to treating your puffer with Prazi, you will also need to perform large water changes for the best results – when I treat my puffers for parasites, I try to change 50% of the water at least every other day. Doing so will not only help you maintain good water quality so that your puffer’s risk of secondary infection is lower, but the water changes will also remove any free-swimming anchorworms so they don’t have time to reach their host.
Make sure you read the instructions on the medication because they may have a different suggestion for the frequency of water changes during treatment.
Some sources suggest manually removing the adult anchor worms with tweezers. However, I don’t recommend trying to pull the parasites out because you will most likely do more damage to your fish than the anchor worm is doing – the parasites that are visibly hanging off of your puffer are very deeply rooted under the skin, and possibly the muscle, as well. If you feel that pulling out the worms is the best route for you, then you should at least consult with a vet before attempting the procedure.
Make sure you are prepared to treat the gaping wound for infection, and don’t leave the head of the anchor worm behind – this will require firmly grasping the anchor worm as closely as possible at the base where it is embedded your puffer’s skin; do not pull in the middle of the parasite’s body or near the tail.
Unless you have a completely cycled quarantine tank, then it will be easier to just keep your puffer where they’re at and treat the entire tank as a whole – this will also help ensure that all stages of the anchorworm are eradicated. However, if you do have a spare tank that’s cycled, you could move your puffer to the sick tank and use dips and spot treatments to get rid of the attached anchorworms – the free swimming larvae that you leave behind will die in a few weeks because they won’t be able to find a host.
Final Words about Treating Puffers for Anchor Worms
If you wake up one day to see a Y-shaped worm dangling off of your freshwater puffer – don’t panic! Although anchor worms can potentially kill a fish because they weaken their immune system which leaves them susceptible to secondary infections, the parasites are more annoying than anything else in most cases – it normally take a large number of anchor worms to weaken a puffer to the point of death.
Always, always watch your puffer for signs of stress when you add a medication directly to the water – you may have to cut the dose in half because they are scaleless fish.
As a side note, many people confuse anchor worms, which again are crustaceans, with planaria, which are flatworms – fortunately, it’s very easy to tell the two apart. In the simplest terms, if you have an infestation of planaria in your fish tank, then you will see the worms all over the glass and possibly free floating in the water – they do not attach to fish.
In fact, they are relatively harmless little creatures and are actually very similar to pest snails in that they are a good warning sign that you are feeding your tank too much – if you see white worms with a triangular head all over your aquarium glass, then your tank has an overabundance of nutrients (and probably too much gravel), so you should really cut back on the amount of food your feed your puffer fish.