Posted 19 January 2010 - 08:35 PM
I have had scuds living in my Aquaclear HOB sponges, though I do not think they were reproducing. I know others have had colonies form in filters. They need some kind of structure- coarse pads, sponges, maybe even ceramic media.
Daphnia cannot handle much flow. You could raise them in a sump refugium with gentle or intermittent current, but I do not think they would do well in a power filter. It would be easier to raise them in a separate container (or preferably containers).
Any pond should have daphnia, copepods, and other microcrustacea. Shallow, fish-free, high nutrient waters such as livestock ponds, leaf-filled forest pools, or temporarily flooded fields (as on some waterfowl reserves) tend to have the highest populations. You should be able to get some even now, but populations are higher in early spring, after algae and plankton populations start to boom but before predatory invert and salamander populations catch up. Any reasonably fine fishnet will work, or make your own with pantyhose.
I have not bred Elassoma, but I expect the fry could handle young daphnia. If not, try an "infusoria" culture. Just crush a small amount grass clippings or lettuce in a container of water and set it out; bacteria will soon colonize it, followed by paramecia, rotifers, and other microorganisms that are a good size for tiny fish. This is also a good way to get mosquito larvae, which adult Elassoma love.
By the way, it will be easier for everyone if you put down your real location. For example, if you live in the Great Lakes area, I would warn you about the possibility of collecting spiny water fleas, an invasive cladoceran that can take over your daphnia colony and which is difficult or unpleasant for small fishes to eat.