One of the simplest live foods aquarists can raise to feed small fish and fry are vinegar eels. These are small worms, about a millimeter long as adults, about the same size as microworms. They tend to swim suspended in the culture liquid, with the greatest concentration visible as a cloudiness in the upper layers.
Vinegar eels can easily be cultured in the fishroom using loosely covered one gallon pickle jars. The cover may be a saucer set on top, a piece of aluminum foil, or a coffee filter or piece of clean material such as old pantyhose or t-shirt, held in place with a rubber band. The cover serves mostly to keep out unwanted pests.
The culture medium consists of equal parts cider vinegar and dechlorinated or tank water, with the addition of either a teaspoon of sugar per quart or a couple of slices of apple. They will appreciate the occasional feeding, but cultures can be safely ignored for months at a time, being long-lived, unusually care free and having no special rquirements.
Harvesting and Feeding
Perhaps the most difficult part of feeding vinegar eels is separating them from their culture medium. Several methods have proven successful, but perhaps the simplest is to suspend a nylon scouring pad (normally used in the kitchen for scrubbing dishes) or a clean piece of nylon stocking or pantyhose in the culture. When you’re ready to feed, remove the material from the culture medium, let it drip for a few minutes or squeeze out gently, then swish in a half cup or so of dechlorinated water. This liquid can then be fed to the fry. Acid buildup from the small amount of vinegar introduced by this method seems to be minor.
Eels can also be recovered by filtering, using a lab or coffee filter, a fine mesh net, or a tightly woven handkerchief. Simply pour a measure of the culture medium through the filter. After returning the liquid to the culture container, rinse out the filter material in water and feed the resulting liquid. Although slower than the scouring pad technique, this method is equally effective.
— G.C.K.A. Newsletter, March 1998