Anchor worms are commonly thought of as a worm, however, it truly is a large parasitic crustacean that attached itself to a fish's skin. The most commonly infected fish are those in which their setups are housed outside, such as with pond fish due to the parasite being able to move from locations during a rainy season. The most common trait that a fish will show when they are infected with anchor worms, is having the appearance of small, thin, white worms dangling from their scales.
Anchor worms are small little crustaceans that are free-swimming and search for fish to bury their bodies into. Sadly, anchor worms can cause serious damage if not treated at the first sign and are one of the most common killers of fish that are placed outside or with other fish that are transferred from different tanks often. This parasite itself can be seen by the naked eye and can reach in sizes from 10-12mm, and tends to look like a small lifeless needle that is sticking out from the scales of the fish.
To understand how to treat anchor worms, we must first understand how they breed and in which stages they can be killed off. In the first stages of infection, the parasite will burrow its head into the fish's scales and dig itself underneath the scales and tissue of the fish. During this stage, only the body and tail can be visible as they are still hanging outside of the fish's body. As the parasite grows, it will reach the juvenile stage in which it will start to mature and finally leave the body of the fish.
If the parasite is a female anchor worm, it will settle on the body of the fish while it still grows to turn into a worm-like shape. As the female gets large enough it will rebury itself inside the fish's skin which can cause damage and be an area in which secondary bacterial infections or fungal infections can grow from. The female will then lay its eggs on the fish's scales where they can fall off and rest at the bottom of the water. Since this parasite has a warm water requirement in order to not die, water temperatures that are below 68oF (20oC) will cause the development of this parasite to stop, causing it to die off (unless it is in the initial egg stage). Any temperature that falls below 57oF (14oC) will cause the females to not be able to lay any eggs at all, hence why this is commonly found in tropical tanks or in species of fish that tend to roam warmer waters compared to cold-water fish. Once the water conditions are correct and the temperature is of an adequate degree, the eggs will hatch and repeat this whole process over again by either infecting a new fish or re-infected the same fish as before.
Treatment and Medication
The treatment of anchor worms can range greatly depending on much water the fish have access to, and how many fish are within the given setup. A common treatment to remove these parasites is to treat the whole tank with potassium permanganate in a ratio of 2mg per .26 gallons of water (2mg per 1 liter). Doing this will change the color of the water (so no need to panic) with the added benefit of not only killing off anchor worms that are attached to a fish, but it will also kill off any eggs that are laying on the substrate. If there are a few fish within the setup, you can always simply just remove the anchor worms using tweezers or do individual potassium permanganate solution baths in a ratio of 10mg per .26 gallons of water (10mg per 1 liter) for about 30 minutes per fish.