Vinegar eels are really a type of nematodes that feeds on the bacteria that make cider into vinegar. They are very tiny and swim in vinegar solution. These are really an easy to raise live fish food. They have limited uses. They are not for adult fish. They are primarily used for fry that are too small to eat brine shrimp or grindal worms. The will grow large enough to eat other foods. Vinegar eels survive fine in plain water but will only reproduce in a vinegar solution.

All you need to raise them is some vinegar, an apple and a container. The container can be any type. I have used empty two liter pop bottle, juice bottles and glass jars. The container size and shape are not important. I use half strength vinegar. You dilute it with distilled or spring water. The best type of vinegar is undistilled vinegar but any type will work. You take a small apple and cut into small piece. If the neck of the bottle is small cut it small enough to fit. When you have placed both the apple pieces and vinegar solution into the container you add the vinegar eels. You put a paper towel over the mouth of the containter. I use a rubber band to hold in place. The purpose to prevent fruit flies from fouling the liquid. The starter culture will seed the solution with bacteria if it is not already present.

A small starter culture might take a month or more to fill a two litter bottle with eels. The eels tend to swim at the top of the solution where most of the oxygen is located in the solution. There are a couple of different ways to harvest them. One is to use a turkey baster to extract them and filter them through a coffee filter. Another method is to use a bottle with a long narrow neck. You place a cotton ball in the neck at the vinegar solution level and gently pour water on the top. You do not want to use plain tap water since it contains chlorine or chloramine which will kill the eels. Dechlorinated or distilled water is best. The water will tend to not mix with the solution and the eels will swim into the water at the top looking for oxygen. You can use the turkey baster to pour them directly into the aquarium. Once the vinegar eel culture is established you can harvest almost daily. This is used mostly with tiny fry like Bettas or Killifish fry. The eels will live for days in fresh water so there is little chance they will die and not be eaten.

I have always used apples. Some people have used apple juice. I have heard from other people that other fruits do not work as well. I have not conducted my own experiments. I think that apples are the cheapest and easiest way to go. Also the apple does not have to pretty.  Bruised apples will do. If you have one that is starting to turn bad it will work fine. They only have to be feed once every few months. You should keep them out of direct sunlight. If the solution evaporates you just add distilled water to top it off. You should keep the liquid at the level that gives the largest surface area. This is how the oxygen gets into the solucation.