by Matt Hirvonen, WAKO
For the purposes of breeding and raising killies, hobbyists have traditionally cultured microworms to feed fry, grindal worms for juveniles(and small killies), and whiteworms to feed adult killies. For those who do not have the time/interest/motivation to maintain multiple worm cultures, I suggest keeping whiteworms alone. Why whiteworms? First they are easy to maintain (see any of the previous KK articles on culturing whiterworms). And second, they are prolific live bearers that deliver fully formed young on a continuous basis. Why is this important? Well, in any healthy culture where the population of whiteworms is expanding, you will find worms of all sizes from the newborn worms (about thrice the size of a large microworm) to adults (over one inch long). So if you can devise a means of sorting the worms by size, you can find worms of an appropriate size for feeding fish that are anywhere from one week old to full grown breeders.
I have been thinking about methods for sorting worms by size for some time. I started using screens of various sizes. But it was too slow, and the worms would thread themselves into the mesh and were difficult to remove. After some time and thought, and several failed attempts (one of the most spectacular failures involved a homemade centrifuge), I rediscovered gravity. So briefly, here is a simple gravity sorting technique. Take a ball of whiteworms (methods for collecting a ball of worms are also discussed in several previous KK articles) and place it in the bottom of a tall glass jar or drinking glass. Now rapidly fill the glass with cold water from your tap, which serves to break apart the ball of worms and get them in motion throughout the glass. As you watch the worms fall to the bottom of the glass you will notice that the big worms settle out first, followed by medium sized worms, and finally the smallest worms. When the majority of large and medium worms are settled to the bottom, simply pour off most of the water (plus the smallest worms) into another glass/jar. You can repeat this process to separate the medium worms from the larger worms as well. It is as easy as that, no kidding.
P.S. very few small worms in your culture is a sign that it is failing, i.e. time to re-culture.