Most recently born fish (fry) in an aquarium will require, or at least grow much better, if they are fed specific foods for them during the first few days or weeks. Baby Brine Shrimp (newly hatched Artemia salina) is probably one of the best known options for fry food.
While definitely not a replacement for baby brine shrimp, microworms make good supplement food for fry, though you could use it as a complete diet if you wish. For a few species too small for baby brine shrimp, microworms will work to get them over the hump to that food. Microworms are small, free-living nematodes. They are also good food for small adult fish, I breed Heterandria formosa and they really enjoy them. Microworms probably aren't the best choice for surface feeding fry such as those of Aplocheilus because they sink slowly. However, you could keep them in suspension with enough current. Here is how I culture them. You will need:
Cups or other similarly sized containers - with lids.
Oatmeal, or cornmeal. Uncooked.
Initial colony of microworms.
You can obtain a starter online by buying it or from another aquarist willing to ship. Microworms reproduce very quickly, so even someone who has just received a starter could hook you up in very short order. Aquarium clubs often have members propagating these worms.
First, clean the container with water - no soap - remember this is fish food. I like yogurt cups, as they come with lids. If you want larger cultures, you can use things like yogurt tubs. Do note that even a tiny yogurt cup produces a whole lot of worms!
Then add your oatmeal or cornmeal. I myself use oatmeal. A 3-5 cm deep layer will suffice - deeper may keep the culture up for longer.
Add water till it is about the consistency of cooked oatmeal. No need to stir, the water should just cover the surface. The oatmeal seems to absorb the water. The surface must not be covered in water (damp, or sopping, but not submerged) when you add microworms.
Add a sprinkle of yeast...enough to cover a little less than a quarter of the surface is what I use.
Use something to scrape microworms from the side of an older culture and then inoculate your new culture. If for some reason shipping went awry don't give up, microworms seem to be able to withstand desiccation for a short time. Try scraping some of the dried "stuff" on the sides and then adding that to your culture. In old cultures where the worms no longer climb the sides, a wet paper towel placed on the surface ought to do the trick. If this is successful, the paper towel will be a milky or yellowish tinge.
Add a lid. Poke airholes for ventilation or leave the lid slightly ajar. Lid keeps mites and mold out for as long as possible.
Soon - give it around a week or so - microworms will begin to crawl up the sides of the container, even earlier than that. If you hold the culture up to light, you can observe the worms wriggling rapidly over the surface. When they start crawling on the sides, use something to scrape them off and feed them to the fish. If you have scraped them all from the sides and still need more, a damp paper towel can be placed over the culture and left for a minute or so and then lifted...it should be coated with microworms.
Before long (anywhere from 2-3 weeks in my experience), the culture will start to go downhill, and soon the only way to harvest will be by the paper towel method. Pay close attention to the ages of your cultures and start new ones accordingly. You can throw the culture out, or use a spoon to clean it out, wash it, and then start over. Be sure you have a spare sink to use if you decide to go by the second method - others will not be pleased with half decomposed blobs of oatmeal and yeast clinging stubbornly to the sink.
On the occasion, a culture will attract mold. Be sure whatever you are using has not expired and is suitable for human consumption. Cultures started from faulty medium will mold or stench almost overnight. Old expired white bread produced the nastiest ever rancid smell I've experienced and needless to say no worms came from those cultures. Sometimes it happens spontaneously to perfectly normal cultures - or otherwise a faulty culture can cause problems with other normal cultures. Dispose of moldy cultures immediately. Do not start new cultures from microworms collected from moldy ones - it doesn't work too well in my experience. Keep ahold of old cultures for as long as possible if they haven't molded - particularly if worms are still crawling up the sides. They could very well save you.
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