Economic Importance for Humans: Positive
Although Daphnia are not used by humans as a food source directly, they are involved in many of the foodchains necessary to sustain fish that we consume or use commercially such as sticklebacks, minnows and young Sockeye salmon. They also are a primary food supply for those animals that trout and many other popular fish depend on. Also, almost any freshwater ecosystem is dependent on Daphnia's ability to convert phytoplankton and decaying matter into a more usable form.
Daphnia are also very frequently used by scientists for experimentation. They are small, cheap, and very easy to keep alive in a laboratory environment. Their almost transparent shell makes their internal functions easier to study and they are very susceptible to changes in temperature, food supplies, or dissolved oxygen content in their environment. Aquarium owners often use Daphnia both as a food source for their fish and to clear the water of debris.