How to Culture Microworms for Your Fish?

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Live food is great for aquarium fish because it provides them with excellent nutrition and the opportunity to hunt as they would in the wild.

The latter caters to the fish’s natural instincts, which will make them happier in the long run. But these are not the only benefits.

Live food options like microworms are also necessary to feed the fish fry. Most fry are too small to consume normal fish food and require a more nutritious diet, aka more protein and fats.

Microworms are great for them because they’re highly nutritious and small, allowing the fry to consume them with ease.

Today, we’ll discuss the best way to ensure a steady supply of microworms for your fish fry, and that’s microworm cultures.

So, let’s get into it!

What are Microworms?

Microworms are tiny nematodes that belong to the Panagrellus genus. They grow up to 3 mm in length and no more than 100 microns in diameter, which makes them 4 times smaller than freshly hatched brine shrimps.

These nematodes can multiply and spread fast, as the female reaches sexual maturity at about 3-4-days of age.

Even more, the female microworm can produce hundreds of tiny offspring during its lifetime; some even go as far as 1,000 or more.

In conclusion, microworms are very small, packed with essential nutrients and fats, and are easy to breed and consume.

It’s understandable why they’re such great options for many species of fish fry. It also doesn’t hurt that they’re relatively easy to culture, which we’ll get into in a second.

What do Microworms Eat?

In one word – carbs. Microworms’ favorite food is oatmeal, preferable with a hint of baker’s yeast for good measure. Other hobbyists use mashed potatoes or various types of cooked grains for the job, which work just as well.

The idea is to use the most appetizing food option that your microworms seem to enjoy the most.

Cooking it is another critical point because high-carb foods are prone to bacterial growth, mold, and even insect infestation.

So, you should boil and mash the microworms’ food into a thick paste to keep it clean and longer-lasting.

A well-designed microworm culture should provide you with a steady supply of live food for your fish fry, given that:

  • An 8-by-12-inch-culture offers approximately one teaspoon of microworms daily for at least 3 weeks
  • Microworms take 3-4 days to reach adulthood and produce up to 40 young per day
  • Microworms have a lifespan of 20-25 days, depending on the species and environmental conditions
  • Female nematodes can produce at least 300 offspring during their lives and up to 1,000 in some cases
  • Microworms consist of 76% water and 24% dry matter, which is a mix of protein and fat
  • Microworms grow up to 6 times their initial size within the first week of life

Now that you know the basics let’s see how you can setup up a sustainable microworm culture.

How to Start a Microworm Culture?

  • Get the starter culture – You need a sample of microworms to get things going. You can get these start cultures online or even at your local fish store since they’re relatively easy to find.
  • Prepare the sustenance – You need a source of carbohydrates. You can go for oatmeal or mashed potatoes since these are readily available, cheap, and easy to prepare. Boil the carbs and mash them into a homogenous paste for ease of consumption. Add a bit of yeast into the mix.
  • Prepare the container – The size of the container depends on how large you want the culture to be. You can start off small with a 5-inch-wide, 3-inch-deep plastic container and go from there in case your culture proves rich and healthy. You add the carb paste, which should be about 1 to 1.5 inches deep. Make sure you balance out the paste’s thickness; you don’t want it too watery, but not too thick either. Spread out the paste evenly to cover the container’s bed completely.
  • Add the microworm culture – You can now add the microworms. A spoonful should suffice since they will multiply fairly fast over the next several days. Spread out the culture evenly to cover the entire surface of the paste.
  • Prepare the lid – You want a lid to cover the culture to prevent flies or other insects from crawling in. Puncture the plastic lid in the middle and carve a decent hole to allow for healthy air circulations. Then stuff the hole with some fabric, preferably cotton, to keep insects out. Make sure that the material you use in the process doesn’t restrict the airflow too severely.
  • Get to the next culture – Once the first container is complete, move on to the next one. You want at least 3-4 different containers for multiple microworm cultures. This is for at least 2 reasons. The first one is having multiple warranties in case one or more cultures fail; which can happen for various reasons. The second one is getting more microworms in case you have a larger fish population that requires more food.
  • Reaping what you sow – Wait out for your culture to expand for about 3-5 days, and then start collecting the worms, depending on your needs. You can have approximately 1 to 1 and a half teaspoons of microworms daily from one optimized culture. The microworms will accumulate on the side of the culture along the container’s walls. You can see them moving in bulks, and you can collect them easily with your finger or a piece of fabric and dump them into the tank.

Make sure you portion the amount of microworms based on the number of fish fry you’re feeding. As a side note, the culture’s temperature will influence its lifespan and outcome.

The higher the temperatures, the faster the microworms will multiply, but the shorter the culture’s lifespan will be.

The ideal temperature for your microworm culture sits at around 68 to 85 °F, depending on your goals.

Why Should You Keep Two Microworm Cultures?

You should preferably keep more than 2 cultures. The reason for that is that microworm cultures can often become contaminated with mold, insects, parasites, and other pathogens that could spoil the whole thing.

I recommend having at least 3 cultures, especially since they’re easy to set up and maintain in the long run.

How do You Know if a Microworm Culture is Dead?

The general lifespan of a microworm culture is approximately 7 days, but this varies depending on environmental conditions and other factors which you may not control.

If you want to get the most out of your microworm culture, keep temperatures around 70 °F and only dispose of it when it gets rancid.

The most obvious signs include a foul smell, and the paste becomes runny like soup.

This is a sign that the yeast already present has taken over and started consuming the carbs; at this point, your microworms are on the decline.

How to Harvest Microworms?

You can use any tool, including your finger. Thriving microworm cultures will have tiny nematodes spread all over the container’s walls, always in close proximity to the food.

Only collect those climbing the walls and ignore the general mass of microworms crowding the carb paste.

Shortly, others will leave the general population and latch onto the walls, allowing them to collect them easier. You should only get the microworms that are separate from the main population to avoid picking off some of the paste as well.

The fish will eat it along with the worms, but many residues will pollute the water. So, try only to grab the microworms and avoid the paste.

How to Maintain a Microworm Culture?

You can’t. The idea is to let the culture run its course and then destroy it and start a new one. The culture will self-destruct primarily due to the worms’ activity.

The microworms will produce waste constantly, soon spoiling the habitat and causing the culture to crash. This generally takes 5-7 days from the starting day.

This is why you should have multiple cultures available to use when one crashes. As a pro tip: set up the cultures several days apart.

This way, you’ll minimize the risk of them spoiling at the same time and leaving you empty-handed.

You can set up another culture when one of your current ones crashes.

Can You Make Microworms without a Starter Culture?

No, you cannot create a microworm culture without a starter. That being said, you will run across numerous articles claiming that you can, but then explain how to obtain your own starter to kick-start your microworm culture.

In other words, they’re talking about setting up a microworm culture without purchasing a starter, which is a different thing entirely.

In this context, yes, you can start your microworm culture without having to purchase a starter.

Here’s how you do it:

  • Cut a meaty potato in half and carve the inside of both of them
  • Bury the 2 halves separately in humid and muddy soil, at least 4-inch deep
  • Wait for approximately 7-10 days for the soil microworms to colonize the decaying potatoes
  • Prepare the container as I’ve explained previously and mix boiled oats, boiled potato, or some bread with yeast diluted in a bit of water
  • Add some of the decaying potatoes filled with the invisible microworms and mix the paste gently
  • Place the lid on, carve the hole on the top, fill it with cotton, and wait
  • Give it at least 3-5 days, and you’ll have a thriving microworm culture, provided everything goes as intended

As you can see, this method still relies on a starter microworm culture. The only difference is that you’ll be making it yourself instead of purchasing it.

Naturally, the whole microworm farming process takes time; at least a week in most cases.

Purchasing your microworm culture directly will help you cut a lot of corners.


Microworms are extremely beneficial to fish fry and small fish species in general. They are highly nutritious and breed fast, providing you with a steady supply of live food for your fish.

It also doesn’t hurt that they’re easy to culture.

Just follow my recommendations, and you’ll soon have several rich microworm cultures with minimal effort.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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