Microworms (Panagrellus redivivus) are tiny nematode worms that make a great fry food. They are an excellent supplement to the popular brine shrimp nauplii, partly because they are smaller in diameter and can thus be taken by fish of a smaller size. Many fish, such as livebearers and most cichlids, can take them immediately upon becoming free-swimming. Smaller fry, such as bettas and danios, can take them after several days of smaller foods. They are not only useful for fry; even small adult fish such as guppies, White Clouds, and neon tetras love them. They are very easy to culture (click here for culture instructions) and produce prolifically. I bought my first microworms via Compuserve FishNet before the Internet was the Internet, and since then I have preferred to have several cultures on hand whenever possible.
Click here to buy a culture of Microworms.