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Micro Worms 101

by Tom Reynolds

Jan/Feb 2009 Issue #44

This article is intended to familiarize the reader with the nematodes commonly referred to as “microworms”.

The nematode genus Panagrellus is currently comprised of 12 species, one of which, Panagrellus redivivus, is widely assumed to be what we raise as “microworms”.

P. redivivus are basically small clear-to-whitish worms, ranging from 1/16” to 1/8” in length, and having a lifespan of 20-30 days depending upon conditions. They are livebearers that start producing young at three days of age, and are capable of giving birth to as many as 40 young every two to five days. Their nutritional value is not quite as good as that of brine shrimp nauplii, but, with proper supplements, can come close.

To begin raising microworms, you must first obtain a starter culture. The best place to do this is from a fellow aquarist with an existing culture.

Next, determine how large of a culture you wish to maintain. You can house them in anything from Petri dishes to plastic sweater boxes, as long as it is water-tight and has a tight-fitting lid. Err on the side of excess here, as having too small of a culture could mean possible starvation of your fry, while a surplus can always be fed to your adult fish. You also need to decide whether you want aeration holes in the lids. My cultures seem to do better with 20-30 tiny holes in the lids (I use Petri dishes).

Once you have found a container, you need to prepare the medium in which the microworms will live and reproduce. The four most common mediums are instant oatmeal, corn meal, wheat flour, and instant mashed potatoes. I have only used oatmeal, but corn meal is rumored to have more of an odor to it, while wheat flour will supposedly contribute to longer culture life, and potatoes will give an average life with minimal odor. Regardless of which one you prefer, the following instructions apply. Place about ¼” of your chosen medium in the bottom of the container, add just enough water to make a paste, then add your starter culture and stir gently. Now is also the time to determine how you want to remove the worms from the container when it’s time to feed the fish. You need to be able to remove the worms without taking the medium, or else you will contaminate the aquarium. The worms will begin crawling up any vertical surfaces in about a week, so one method is to use a finger or a Q-tip to simply wipe them off the sides of the container. If you aren’t too keen on touching them, there are two other ways, one using Bio-Balls, and the other using a paper towel. The first method involves laying three Bio-Balls in a triangle on the medium, then placing a fourth on top to form a pyramid. The worms will climb up to this top ball, which can then be removed and dunked in the fry tank. The second method involves laying a piece of wet paper towel directly on top of the medium and leaving it until it’s covered with worms. Then take a spoon and gently scrape them off, taking care not to tear the paper towel. Once you’ve made a decision, close the lid and put the culture someplace where it will not be exposed to temperature fluctuations.

You will need to feed your cultures periodically; I usually add a pinch of oats (not instant) every two to four days. If a culture becomes too runny, simply add a small amount of the original medium. If it gets too dry, add a little water. If you have a large number of worms, but they aren’t crawling up the sides after a week or so, try cutting back on the aeration. A lack of fresh air seems to make them crawl up the sides much faster.

Your culture should last three to six weeks, depending on temperature and aeration. You’ll begin to notice a change in both the color (darker) and odor (nastier) after a few weeks. You may also notice that the culture is not reproducing as rapidly. When this happens, it’s time to divide the culture. This is easier to do when you’re using smaller containers – it’s much easier to find room for ten Petri dishes than ten sweater boxes. If you are using more of the same size container, simply divide the original culture into three or four sections, scrape off only the top layer of the culture, and place it in the fresh medium of the new container, following the instructions previously given.

The End