Vinegar eels can be raised in a similar fashion than microworms. The benefit of this method is that it produces a much denser population of worms than the traditional method.
50/50 water-vinegar mix is used to prepare the medium. I use oatmeal with some wheat flour mixed in.
Unlike microworms, vinegar eels can swim and will remain in the water until they get eaten. They are indeed my top choice for small fish fry.
Package includes a starter culture from a healthy culture of my own. EU/UK shipping - 4€ as priority envelope.