Pet Keen is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

Goldfish Lice & Anchor Worm

Fish Skin infected

Keeping goldfish isn’t always the most glamorous job. You have to manage dirty tank water and deal with some of the biggest water piggies in freshwater home aquariums. Honestly, few things make you feel less glamorous than being covered in dirty fish water while your goldfish beg for food. That is until you deal with parasites on your goldfish for the first time. These creepy-crawlies can be more than unsettling, though. They can be uncomfortable and deadly for your goldfish. Keep reading for more information on goldfish lice and anchor worms.divider-fish

What are Fish Lice?

Goldfish lice are a type of crustacean known as copepods, and they go by the scientific name Argulus trilineatus. They measure approximately 3-4mm when fully grown and are translucent, which can make them difficult to spot within your tank or on your fish. Males tend to be slightly smaller than females.

Fish lice use a needle-like mouthpart to suck blood from fish, much like a mosquito. If you can get a close look at fish lice, they are usually rounded and almost alien in appearance. These parasites are highly contagious and can rapidly spread throughout an entire tank if they are not caught and treated early enough.

What are Anchor Worms?

Like fish lice, anchor worms are also copepod crustaceans. These crustaceans go by the scientific name Lernaea cyprinacea and are easier to spot than fish lice. Anchor worms attach to a fish via their mouthpart while their body juts out from the body of the fish. Anchor worms are ribbon-like and pretty recognizable as parasites when you spot them.

Anchor worms are highly contagious and will quickly infest your whole tank. They can create lesions on your goldfish’s skin, leading to scale loss. They are frequently spotted in and around the gills and gill covers. Sometimes, they aren’t particularly noticeable until you see them moving as your fish’s gills open and close with respiration.

If your fish isn't behaving or looking as it normally does and you suspect it may be sick, ensure you provide the right treatment, by checking out the best-selling and comprehensive book The Truth About Goldfish on Amazon today.

The Truth About Goldfish New Edition

It has entire chapters dedicated to in-depth diagnoses, treatment options, a treatment index, and a list of everything in our fishkeeping medicine cabinet, natural and commercial (and more!).

What are the Symptoms of Fish Lice and Anchor Worms?

Fish lice are visible on goldfish, although they can be difficult to see. They usually show up as small, greenish dots or flecks across the body of your goldfish. Anchor worms, on the other hand, appear as small, white, ribbon-like worms that hang out from the body of the fish, usually by sticking out from between scales.

Goldfish with fish lice or anchor worm will often exhibit flashing, which is a behavior that involves rapidly darting around the tank and attempting to rub up against items within the tank. Flashing indicates itching or discomfort and is usually done in an attempt to eliminate this sensation. Other symptoms may include fin clamping, rapid breathing, pale coloration of the gills, lethargy, and inappetence.

How Can I Treat Goldfish Lice and Anchor Worm?

If left untreated, fish lice and anchor worms can lead to severe anemia, secondary infections, and death. Both of these parasites will reproduce and spread within your tank until they are treated. The most effective treatment for fish lice is medications with cyromazine as the active ingredient. Cyromazine is an antiparasitic that works by limiting the parasite’s ability to produce and maintain its exoskeleton. Without an exoskeleton, these creatures will die. While cyromazine is a highly effective treatment for fish lice and anchor worms, it is unlikely to kill all of the parasites within a few days due to its mechanism of action.

If you’ve treated your fish with cyromazine and are still seeing indications of an active infestation, you may need to continue or repeat the treatment. Make sure to carefully follow the instructions on the product you are using, though. Since this is an antiparasitic medication, an overdose can kill your goldfish and anything else in the tank with it.

You May Also Like: 20 Goldfish Diseases You Can Treat and Prevent

How Can I Prevent Goldfish Lice and Anchor Worms?

Due to the contagious nature of both of these pests, the best treatment is prevention. Both parasites can weasel their way into your tank via new fish or plants, or via infected water, like if you were to introduce a fish from the local pet store directly into your tank. The best prevention for parasites like these is to initiate a quarantine protocol for new fish and plants before you introduce them to your tank. Plants can be quarantined or given a bleach or hydrogen peroxide dip, but new fish and other animals should be quarantined in a separate tank for two weeks, at minimum. Ideally, a fish’s quarantine should last from 4-8 weeks to ensure you’ve had ample time to monitor for signs and symptoms of parasites and other illnesses.

Maintaining good water quality can help prevent and treat fish lice and anchor worm. Routine water changes can help remove eggs and free-swimming parasites in the water column. This can be especially important if you are treating a pond or a tank that you intend to allow to overwinter in cold temperatures. At the end of the season, it’s a good idea to thoroughly clean the pond or tank to avoid having a full-blown infestation on your hands once the warm temperatures roll back around.


In Conclusion

Fish lice and anchor worm are creepy and unsettling creatures to spot in your tank, but they can be treated. Your best chance of keeping your tank safe and protecting your fish is preventing these parasites in the first place. However, sometimes this isn’t possible, in which case, early identification and treatment gives your fish the best shot at survival with few complications. It’s good practice to visually inspect your fish at least a couple of times per week to ensure you don’t see any evidence of parasites on the skin, scales, gills, or fins. Catching parasites early will make treating them so much easier!

Featured Image Credit: NatureDiver, Shutterstock

Our vets

Want to talk to a vet online?

Whether you have concerns about your dog, cat, or other pet, trained vets have the answers!

Our vets

Before you go - Don't miss out!