What microworms are
The microworm (Panagrellus redivivus) is a free-living nematode just over 1 mm long and about 50 µm thick, barely visible on its own. It lives on yeast, which is why it grows so easily on a flour or oat paste with yeast added. It is harmless to fish and people and is used in fish farming as a first food for newly hatched fry.
Two close relatives are kept the same way: banana worms (Panagrellus nepenthicola) and walter worms. Both are a little smaller than microworms, banana worms the smallest of the three, which suits fry with the tiniest mouths, such as those of bettas and rainbowfish. Everything below works for all three.
Starting a culture
- Cook or soak plain oatmeal (no sugar or flavoring) into a thick paste and spread it about half an inch deep in a small plastic tub.
- Sprinkle a pinch of dry baker’s yeast over it.
- Add a spoonful of an existing culture from a fish club, a breeder or a starter culture.
- Put the lid on with a few small holes and keep it at room temperature, out of the sun.
In a few days the surface moves, and worms gather on the sides of the tub.
Harvesting and feeding
Wipe the worms off the sides with a clean finger, a cotton swab or a small brush and swirl them into the fry tank. They sink and wriggle on the bottom for a while, where fry pick them off, so feed only what the fry clear up in a few hours. Feed small amounts several times a day. Fry that need even smaller food in their first days start on infusoria. Feeding fry
Keeping it going
A culture goes sour and watery after a week or two. Start a new tub from a spoonful of the old one every week or so and keep two going at once, so one failing does not leave you without. A strong smell is normal; mold, or no worms moving, means start again.