Water flea

Water flea is a generic term for a number of small aquatic crustacea characterised by their jumping or jerky mode of swimming. Most are between 0.1 mm and 3 mm in length. Most commonly, they will be species of Daphnia but a number of other genera are also commonly included, including Cyclops, and Diaptomus. Water fleas are commonly sold as aquarium food since they are easy to culture and reproduce rapidly. They are capable of existing in salt or fresh water, thouygh different species inhabit each region. There are over 100 species of water flea.

Anatomy

The water flea's body is encased in a shell which is transparent and helps prevent predation. They are commonly studied by students due to the fact that their internal organs can be seen easily. Though the shell appears to be segmented, it is actually composed of only one piece. The water flea has five pairs of leaf like legs which bear gills and filter food.

Reproduction

Water fleas reproduce in the both the summer and winter months months. The development of their eggs does not require fertilization in summer and they reproduce A sexualy bearing live young. Near the summer's end or in the event of say a pond drying up. the male eggs hatch and proceed to fertilize the eggs in the females. These develop into the "winter eggs" or "stress eggs" which add genetic variation. such eggs can last 100's of years in dry dusty conditions and blow to new areas by wind, upon contact with water (above 2 degrees c)they will hatch into females and the process starts a new. Daphnia.nzed.com/breeding, an online resource on the reproduction of daphnia

Invasive Species

The "spiny water flea", Bythotrephes cederstroemi, is causing serious concerns in the lakes of Canada. The problem is that it feeds on zooplankton and can actually eliminate zooplankton species. As zooplankton is the backbone of aquatic food chains, this tiny crustacean presents a serious risk to the ecosystem. The eggs survive even after being dried out or eaten by fish.

See Also

• Plankton
• Daphnia