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Types of White Worms in Fish Tanks

white worms in fish tank

With any hobby and pet keeping, there can be bumps along your journey. Underwater ecosystems are one of those hobbies that will bring countless hours of enjoyment, but some people may encounter things that make you scratch your head in confusion. One of those head scratchers may come from seeing some little worms crawling within the substrate or along the glass.

So, what are these little white worms and how did they get there? Don’t overreact, we first need to identify what they are before devising a solution. There are numerous different types of worms that can affect aquatic life such as, Camallanus and anchor worms, but today we are focused more specifically on three types of worms that can plague aquariums, Detritus, Rhabdocoela  and Planaria.

Detritus Worms

Detritus worms is a broad grouping that encompasses the phylum Annelida which includes species like leeches and earthworms. These little worms resemble white, reddish/brown, or gray strings and move very similarly to an earthworm.  Although the thing out of nightmares, these little wiggly worms are fairly common throughout the aquatic hobby and most aquarists have them and may not even know it.  These worms are not harmful to fish and can be a beneficial addition to the aquarium. As the name implies, detritus worms feed off of and break down decaying matter within the substrate.

Although not harmful, detritus worms are not something most aquarists want to see when they are peering into their aquarium. These worms typically explode in population due to overfeeding and reduced maintenance. Like most living things, detritus worms require oxygen and if oxygen level drops the worms will start emerging from the substrate.

The easiest and safest way to rid your tank of excessive worm populations is by reducing feeding and increasing your tank maintenance program. Gravel siphoning will help remove these worms during the water change process. To keep your water quality at its best, ensure you are not overfeeding your aquatic life and are completing a 20% – 25% water change monthly.

Rhabdocoela Worms

Rhabdocoela worms are a common flatworm in the Rhabditophora class. Like detritus worms, these flatworms’ make up the natural ecosystem in the tank. They are harmless to aquatic life, feeding on bacteria and microalgae.

Rhabdocoela are very tiny in size and will seldom grow over 0.2 inches in length. Rhabdocoela have two round ends unlike the typical triangle shaped head of the bigger Planaria.  Their population growth is similar to detritus worms and are typically a result of too many nutrients in the aquarium. Reducing their food source and vacuuming the gravel will help keep their numbers in check. Some predatory fish may also find Rhabdocoela to be a tasty snack.

Planaria (Flatworms)

Planaria, also known as flatworms, are part of the class Turbellaria, closely related to tapeworms and flukes, another parasitic flatworm. Flatworms can be found in both saltwater and freshwater environments. Their color can vary from white, reddish-browns, black and even pink based on what they are feeding on. Unlike the long-rounded body of the detritus worm, these flatworms are smaller in size, flattened bodied, with a distinct triangular shaped head containing two eyespots.

Planaria are not easily removed from an aquarium once infected. These usually enter the aquarium by hitchhiking on an infected source. These worms are continuously seeking out a meaty meal, readily consuming unconsumed food. Planaria typically are unable to attach to a swimming fish or fast-moving invertebrate but will take the opportunity to take a bite out of an unsuspecting or resting shrimp or fish. These worms are most problematic to anyone trying to breed, as they will feed on shrimp, snail and fish eggs as well as any small fry and baby shrimp they can catch.

Flatworms are masters of reproduction. If cut into pieces, planaria are capable of regenerating into complete organisms from each piece. Planaria can only be controlled by conventional methods like reduced feedings, gravel vacuuming and water changes but unfortunately these methods will not fully remove them from the aquarium. The most effective way of fully eradicating a planaria infestation is to use a de-worming medication. Products like Fish Bendazole (Fenbendazole), API’s General Cure, and Clout have had successful results. Caution and care must be taken when using any medications though as there are several fish species and invertebrates which can be extremely sensitive to medication. Ensure you adhere to the instructions provided by manufacturer as improper usage could result in harm to your aquatic life. Also be prepared to complete water changes, as large populations of dying planaria can cause the ammonia to spike.

While worm infestations may be scary, knowing exactly what you are dealing with will help you create a plan of attack. Better yet, ward of these wiggly unwanted guests by properly feeding your aquatic life and setting up a routine maintenance schedule for your aquarium.

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Reviewed by Petco’s Animal Care, Education and Compliance (ACE) Team

Petco’s ACE team is a passionate group of experienced pet care experts dedicated to supporting the overall health & wellness of pets. The ACE team works to develop animal care operations and standards across the organization and promote proper animal care and education for Pet Care Center partners and pet parents, while also ensuring regulatory compliance.