popularly known as water fleas, are small crustaceans that live in fresh water
such as ponds, lakes, and streams. They serve as an important source of food
for fish and other aquatic organisms. Daphnia are excellent organisms to use
in bioassays because they are sensitive to changes in water chemistry and are
simple and inexpensive to raise in an aquarium. They mature in just a few days,
so it does not take long to grow a culture of test organisms.
Because Daphnia are transparent, it is possible to conduct
bioassays using endpoints other than death. For example, through
a microscope you can measure their heart rate or observe whether
they have been eating. (Both of these signs are used to measure
stress). If you are worried about killing Daphnia in your experiments,
you could choose to measure one of these other endpoints instead.
It is worth keeping in mind, though, that even under the best
conditions these organisms live only a month or two, and in nature
most of them get eaten within their first few days or weeks of
Bioassays Using Salt
More information about Daphnia
to Environmental Stress
Other bioassay links
How are bioassays used in
the real world?
Lettuce Seed Bioassays