| Water fleas | ||||||||||
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Suborder Anomopoda Daphniidae Moinidae Bosminidae Macrothricidae Chydoridae Suborder Ctenopoda Sididae Holopedidae Suborder Onychopoda Polyphemidae Cercopagidae Podonidae Suborder Haplopoda Leptodoridae |
Water fleas are the order Cladocera of crustaceans, who are so named because they tend to swim by making little jumps.
Water fleas are small, between 0.2 and 3 mm in length. They inhabit in various types of environments ranging from acidic swamps, lakes, ponds, streams (freshwater), to marine water in some cases. Some are kept as live food for aquarium fishes mainly because they are very easy to culture (high reproduction rate) and helps in keeping the aquarium water clean on account of their feeding habit. They are also used as a bio-indicator to monitor water quality due to their high sensitivity to toxins and other biologically harmful chemicals in the water supplies.
The division of the body into segments is nearly invisible. The head is fused, and is generally bent down towards the body with a visible notch separating the two. In most species the rest of the body is covered by a carapace, with a ventral gap in which lie the five or six pairs of legs. The most prominent features are the compound eyes, the second antennae, and a pair of abdominal setae.
A few water fleas are predatory on tiny crustaceans and rotifers, but most are filter feeders, ingesting various sorts of organic detritus including protists and bacteria. Daphnia can be kept easily on a diet of yeast. Beating of the legs produces a constant current through the carapace which brings such material into the digestive tract. The first and second pair of legs are used in the organisms filter feeding, ensuring large unabsorbable particles are kept out while the other sets of legs create the stream of water rushing into the organism. Swimming, on the other hand, is powered mainly by the second set of antennae which are larger in size than the first set. The motion of thes second set of antennae are responsible for the jumping motion.
Daphnia reproduce pathonogenetically usually in the spring till end of the summer. The newly hatched flea out of the brood must molt several times before they are fully grown into an adult where their first clutch of eggs are ready in their own brood chamber (usually after about two weeks). The fully mature females are able produce up to one-hundred eggs every three days and will continue to produce new generation of females about every ten days. The reproduction process continues until the water is overcrowded with them, usually towards the end of summer where winter conditions brings an end to the procession of new female generations. At this time, their reproduction method changes. They produce male eggs which results in mating and fertilization of the eggs. Fertilized eggs are termed winter eggs, provided with extra shell layer called ephippium. The extra layer preserves and protects the egg inside from harsh winter conditions until the following spring when the reproduction cycle is able to take place once again.
Males are only found at times of harsh environmental conditions, typically during portions of the year of scarce resources due to population overgrowth or winter conditions, and even then may make up considerably less than half the population, in some species being unknown entirely. They are much smaller in size than the female. Their appearance is for the creation of resting eggs or another term winter eggs which allows for the survival of the population through the harsh conditions.
The lifespan of water flea does not exceed one year and is largely temperature dependent. For example, individual organisms can live up to 108 days at three degreex celsius while some organisms live for only 29 days at 28 degrees celsius. A clear exception to this trend is during the winter time in which harsh conditions limit the population in which females have been recorded to live for over 6 months. These females generally grow at slower rate and larger than ones under normal conditions.
Taxonomy
Order: Cladocera Latreille, 1829
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