Microworms are absolutely tiny worms, fed by aquarists to newly hatched fish fry. Whilst not as nutritious as newly hatched Artemia (brine shrimp), they are incredibly easy to culture and, with a small amount of work, offer a permanent, clean, and effectively free, source of fry food, available whenever needed.
As stated above, there is no substitute for Artemia when raising a batch of fry, and any batch fed exclusively on microworm will not grow as quickly, or have the same survival rate as with shrimp. Having said this microworms do offer a good meal for those fry that spend their time near the tank floor, and few serious fish breeders would be without a culture or two.
Microworms are also useful in aiding egg hatching; aswell as supplying a first meal for the new fry, a few worms amongst some developed, but unhatched eggs can actually lead some stubborn fry to emerge.
How to Culture MicrowormsMicroworm cultures
The media (food) in which the worms live is quite important - get this wrong and the culture will crash, resulting in a smelly mess. Luckily, getting it right is not hard. There are several recipes, but one of the best is simply a spoon or two of finely milled oat breakfast cereal (Ready brek, etc) and roughly the same amount of water. The mix should be a gloopy liquid, but not overly runny.
The worms can be kept in a small plastic container, with a few holes for ventilation. Make sure these holes are really small though, as fruit flies may well move in otherwise. A small amount of starter culture should be added to a few millimetres deep of media. The worms will rapidly reproduce, feeding on the surface of the oat mix. The surface will soon show considerable movement of wriggling worms. As the culture matures, worms will start to crawl up the sides (see pic above) at which point they may be scraped off for feeding to fish.
If the culture gets too dry, wet it lightly with a water mister. When doing well the culture may also get a little too wet. requiring a gentle sprinkling of more ground oats. Eventually, the culture will start to smell (usually after a week or more). At this point they must be subcultured; collect some worms and add them to a clean container of fresh media.
How to Use Microworms in the Aquarium
Feeding fry with microworms is as simple as scraping them off the sides of their container with a small stick and swirling it into the tank that needs feeding. They do not require any rinsing, but care must be taken to avoid adding the culture media to the tank; only use worms that have crawled up and out of their food. The worms will sink slowly, but can survive for sometime underwater. In general, microworms should not be fed to tanks with a substrate - they will quickly sink, get lost amongst the gravel, die and polute tank water. Snails will eat them up, but once they are 'in' the gravel, even snails might not be able to find them. Microworms are best fed to fry in bare bottomed tanks.
Sometimes it is better to swirl the collect worms into a small volume of water, and feed them in smaller quantities with a pipette - allowing fish of all sizes to feed upon them as they sink.