Anchor Worms in Freshwater Fish

Anchor worms (Lernaea spp.) are macroscopic parasites, meaning they can be seen with the naked eye. They are common in koi and goldfish, but are also found in many freshwater fish species. The “worm” part protruding into the water are actually the female reproductive structures. Treating these parasites can be challenging depending on your configuration and parasite load.

What are anchor worms?

Anchor worms (Lernaea spp.) are external copepod parasites that attach themselves to your fish under scales. These parasites have several non-parasitic stages that take place in the water. Once a male mates with a female, it attaches itself to a fish to mature into a reproductively active adult. These parasites get the name “worm” from the spreading female reproductive structure. Youngsters can swim freely in your aquarium, but they are not a nuisance for your fish.

That Lernaea Copepods infect most freshwater fish. They are most common in goldfish and koi. There are other similar species of copepods that infect other freshwater species and marine fish.

Sign of the anchor worms

Anchor worms are one of the macroscopic freshwater fish parasites that are visible to the naked eye. You will see the female reproductive structures that resemble short white worms protruding from behind scales. Anchor worms can also be found in the oral cavity and give the mouth a “whisker” effect.

Worms that have fallen off can cause bleeding or fibrosis.

Causes of anchor worms

Anchor worms arise when a new fish is added to an aquarium that has juvenile anchor worms or a reproductively active female in the skin. By skipping the correct quarantine, this parasite spreads very quickly. A single female anchor worm can produce hundreds of larvae in a 77F (25C) tank every two weeks for up to 16 weeks.

Anchorworm pups can also be spread with the introduction of live plants. Although they may not be on the plants, free-swimming juveniles may be in the water surrounding the plants. Aquatic plants can bring a lot of bacteria and parasites into your aquarium if not properly quarantined. As with quarantining your new fish, quarantining plants in a plant-only system disrupts the parasite’s life cycle as there are no fish to house it. This only applies to plants that are kept with fish. If your new plants have never been fish-kept, they are disease free. This doesn’t mean they can transmit some invertebrate pests!

Treatment of anchor worms

Once anchor worms are present on your fish, it is very tempting to just peel them off but resist the urge to do so. Anchor worms must be properly removed by your vet from a sedated fish. You need to remove all of the parasite from the feeding end. Depending on the degree of infestation, the sedation puts less stress on the fish and the vet can work more effectively without the fish having to squirm.

With the mature females removed, you may still have a microscopic problem: the juvenile stages. Over-the-counter “anchor worm” treatments are usually quite effective against the adolescent stages, but they won’t affect the adults. This can also be achieved by removing the substrate and decor and letting the water run through UV light.

Treatment of anchor worms with organophosphates or diflubenzuron (Dimilin) ​​is effective but must be done with extreme caution. Use only veterinary approved products, keep them away from your other pets, and wear appropriate protection (i.e. gloves).

Adult binding sites can also develop secondary bacterial infections. Monitor these areas carefully after the adults are removed. Depending on its location and severity, a second treatment with antibiotics may be necessary. Antibiotics should not be bought over the counter and should only be used with a prescription. The best way to prevent these infections is with good quality water.

Preventing anchor worms

The best way to prevent anchor worms is to properly quarantine any newly added files. If you see anchor worms in a fish tank that you are about to buy, assume they are all contaminated. Remember, juvenile larvae are microscopic and can be present without you even realizing it until it’s too late. By properly quarantining your new fish, you will prevent it from getting into the main tank.