What are Microworms?
Microworms (Panagrellus redivivus) are small free-living nematodes popular amongst fish breeders as live fish food for small juveniles and 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 is a tiny worm species growing just over 1 mm long. They live on yeast and can be easily cultured by aquarium hobbyists on flour or mashed potatoes substrate.
Microworms are completely harmless to humans and are not parasitic. They are a great source of live food for tiny fish fry, which are too small to eat larger types of food. While they only live 8 to 12 hours in the 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 that 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 ensure your fish fry has access to a varied diet of live and prepared foods.
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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 the tank water. These worms will live for 8 to 12 hours in freshwater, 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.
How to Culture Microworms
Culturing microworms is easy and only takes a small about of readily available equipment. You’ll need to know some things when growing this popular live fish food. We’ve compiled a step-by-step list of what you’ll need to do when growing microworms for your fish fry.
1. Prepare 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, and un-chlorinated or RODI water. Microworm starter culture can come from a number of different sources, including online sources, local fish stores, or even one of your own spent microworm batches.
It’s important to ensure 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 extra additives.
2. Prepare Growing Containers
You’ll want breathing holes in your microworm growing containers, which 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 to know how long each batch has grown. 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 end up with a soupy mess. Too little water and your microworms won’t have the 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 it 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 to ensure a steady supply of fish food. If you see a batch that is getting moldy, smelling spoiled or 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. Feed what your fry will eat, and do not overfeed to avoid water quality problems.
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 ensure 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 ensure 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 that can spoil growing batches and harm small fish fry. While some Microworms live in soil, there are 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 like 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, cultivating a few different types of small worms can be a good idea.
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 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 Grindal worm colonies, last longer than Microworm or other small worm colonies.
A growing substrate with Grindal worms can be harvested much longer than Microworms, and since it isn’t based on mashed potatoes or other starch, it 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 with difficulty eating 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 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.