Microworms Culture as Live Fish Food: The Ultimate Guide


What are Microworms (Panagrellus redivivus)

Microworms (Panagrellus redivivus) are a small free-living nematode which is popular amongst fish breeders as a live fish food for small fish fry. Sometimes called the “beer mat nematode,” due to their occurrence in constantly moist felt beer mats. It is a common species first discovered in 1776. Panagrellus redivivus are a tiny worm species which grows to just over 1 mm in length. They live on yeast and can be easily cultured by aquarium hobbyists on a substrate of flour or mashed potatoes. Microworms are completely harmless to humans and are not parasitic. They are a great source of live food for tiny fish fry who are too small to eat larger types of food. While they only live 8 to 12 hours in water, this is usually enough time for fish fry to find and eat them. Fish breeders looking to feed fry with Microworms should consider varying their diet with other types of fry food, both prepared and live, such as brine shrimp. Some breeders have noted fish deformities which result when feeding a diet exclusively of Microworms. This may be caused by impurities introduced from growing media and not because of Microworms exclusively. Whatever the reason, it’s always best to make sure your fish fry have access to a varied diet of live and prepared foods.

Use of Microworms as Live Fish Food

Microworms are a great first food for tiny fry who have difficulty eating larger foods such as brine shrimp. Brine shrimp are popular with fish breeders but can grow larger than some tiny types of fry can eat. Microworms are popular with Betta breeders because their small size makes for an ideal first food for Betta fry. They are also popular with breeders of other fish with tiny fry such as Angelfish, Guppies,  Platy, Killifish, and Neon Tetras. Feeding is easy as Microworms can be wiped off the walls of their growing containers and introduced directly to tank water. These worms will live for 8 to 12 hours in fresh water which is usually enough time for tiny fry to find and eat them. It is important not to overfeed Microworms as if they aren’t eaten they will eventually die and can spoil tank water.

Microworms (Panagrellus redivivus)
Microworm Culture

How to Culture Microworms

Culturing microworms is easy and only takes a small about of readily available equipment. There are some things you’ll need to know when growing this popular live fish food. We’ve put together a step-by-step list of what you’ll need to do when growing microworms for your fish fry.

1. Assemble your microworm growing materials

To begin growing your own microworms you’ll need: microworm starter culture, plain instant mashed potatoes, small plastic containers with tall sides and tight fitting lids, un-chlorinated or RODI water. Microworm starter culture can come from a number of different sources, including on-line sources, local fish stores, or even one of your own spent microworm batches. It’s important to make sure the instant mashed potatoes are plain, and don’t contain any flavorings or other extra ingredients. Read labels carefully to be sure you’re getting a pure product without any extra additives.

2. Prepare microworm growing containers

You’ll want breathing holes in your microworm growing containers but these must be sealed to prevent the worms from crawling out. The best way to handle this is to cut openings in the lids and tape a piece of coffee filter or filter floss across the hole. This lets your microworm cultures get fresh air but will prevent dirt and insects from getting in, or the worms from getting out. Label the containers with a date so you know how long each batch has been growing. You’ll likely run more than one microworm culture at a time, and keeping track of dates will be important.

3. Growing microworms

Start by placing a half-inch layer of instant mashed potatoes in the bottom of each container. Add enough un-chlorinated or RODI water to give it the texture of fluffy mashed potatoes. You don’t want to use too much water or you’ll end up with a soupy mess. Too little water and your microworms won’t have the right conditions to grow. Some people add yeast to this mix, but this is optional and may not make a difference. Finally, spread the microworm starter culture over the surface of the mix and seal with one of the prepared lids. Store these containers at room temperature, and away from direct sunlight. You’ll likely want to prepare a few growing containers as not all microworm batches are successful and you’ll want enough batches going to ensure a steady supply of fish food. If you see a batch that is getting moldy, smelling spoiled or is infested with bugs you’ll want to discard this batch. Avoid feeding fish fry with microworms from cultures that aren’t healthy and thriving.

4. Harvesting microworms and feeding fry

Once your colonies of microworms start growing you will see the tiny worms crawling up the sides of the plastic containers. Use a finger or cotton swab to wipe along the sides of the container and remove the worms. Rinse your finger or swab directly into the tank to feed your fish fry. Microworms will only live around 8 to 12 hours in tank water, after this they die and can spoil tank water. Only feed what your fry will eat, and make sure to not overfeed to avoid water quality problems.

Microworms (Panagrellus redivivus)
Microworms in Aquarium

5. Starting new microworm cultures

Not all microworm cultures will be successful: some will spoil and these should be thrown out. This is why it’s a good idea to start multiple cultures to make sure you have enough food for your fish fry. Even cultures that don’t spoil will eventually produce fewer and fewer worms. You can use some of the worms and mash from these as starter cultures for new batches. You can reuse your old growing containers but make sure they are thoroughly washed and dried first. Replace any contaminated vent hole coverings and make new ones as needed.

Where to find Live Microworm Culture for Sale

Microworm cultures are easily available online and from local fish stores. If you know other fish breeders in your area you may be able to get a starter culture from one of their batches. Microworm starter cultures are cheap: expect to pay around $5 USD, plus shipping if buying online. It is best to use a prepared starter culture instead of attempting to collect Microworms in the “wild.” Wild sources may introduce other types of worms and pests which can spoil growing batches and might even harm small fish fry. While some Microworms do live in soil, there are also other types of worms so it can be difficult to isolate only the worms you want. It is always best to use Microworm starter cultures from reputable sources which can vouch for their purity and viability.

Microworms vs Walter Worms

Walter worms are smaller than Microworms (Panagrellus redivivus) but larger than banana worms. They can be a good choice when feeding very small fry who may have trouble eating larger food. They can be cultivated the same way as Panagrellus redivivus so making a batch of Walter worms is as easy as buying the correct starter culture. If you want to give your fish fry a varied diet it can be a good idea to cultivate a few different types of small worms. While Walter worms have similar nutritional profiles as Banana worms and Panagrellus redivivus, giving your fish fry a varied diet can benefit their growth and they may appreciate some variation in their diets!

Microworms vs Grindal Worms

Grindal worms (Enchytraeus buchholzi) are another small live food that aquarium hobbyists cultivate for fry food. Cultivating Grindal worms is a bit different and requires a soil growing substrate instead of mashed potatoes. These worms can be used in place of Microworms and it really comes down to personal preference. Some fish breeders like the fact that Grindal worm colonies last longer than Microworm or other small worm colonies. A growing substrate with Grindal worms can be harvested for a much longer time than Microworms and since it isn’t based on mashed potatoes, or other starch, will not spoil and can be harvested for months!

Microworms vs Banana Worms

Banana worms are smaller than both Panagrellus redivivus and Walter worms. Banana worms are a great choice for feeding exceptionally small fish fry who have difficulty eating any but the smallest foods. Banana worms are cultivated in the same way as Panagrellus redivivus and Walter worms so raising them only involves switching to a different type of starter culture. Banana worms have the same nutritional profile as many other small worms used for fry food. There is no nutritional advantage to feeding one type over another. Finding the appropriate fry food is only a matter of deciding how small live food should be for your particular fish fry.

Fish Laboratory

With decades of collective fishkeeping experience, we are happy to share the fish care tips that we've picked up along the way. Our goal at Fish Laboratory is to keep publishing accurate content to help fishkeepers keep their fish and aquarium healthy.

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