Some Daphnia info

Discussion in 'General Aquatic Talk' started by Peter, Nov 13, 2007.

  1. Peter
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    Peter Algae harvester

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    Hi

    I think the majority of us are aware of Daphnia and how they work in the food chain, but I thought it would be nice to know more about these little creatures. In my mini study I can share what I have learnt with regards to what they feed, life span, reproduction and other uses besides as a food source. The below photo?s are allowed by the sources of my research, provided, they are used only in a public domain and I take no credit of creation, however, there is one photo that took me hours to get right.

    The interest for me was when I noticed different types of Daphnia from what I?ve been used to in my culture tank as well as hearing of red Daphnia and it triggered my curiosity. I found 36 species of Daphnia that range between 0.2mm and 5mm in size. The life span will depend on the conditions of its environment, but lets say they are perfect for a species, it can live up to a year. In a temperature of 3 degrees C it can live up to 108 days, which possibly explains why we have some survivors during our winter but in a temp of 28 degrees C up to 29 days


    Anatomy of Daphnia.

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    ?Daphnia reproduce parthenogenetically usually in the spring until the end of the summer. One or more juvenile animals are nurtured in the brood pouch inside the carapace.The newly hatched Daphnia must moult several times before they are fully grown into an adult usually after about two weeks. The young are small copies of the adult; there are no true nymphal or instar stages. The fully mature females are able to produce a new brood of young about every ten days under ideal conditions. The reproduction process continues while the environmental conditions continue to
    support their growth. When winter approaches or in drought conditions or at times of other harsh environmental conditions, production of new female generations cease and parthenogenic males are produced. However, even in harsh environmental conditions males may make up considerably less than half the population, in some species they are unknown entirely. Males are much smaller in size than the female and they typically possess a specialised abdominal appendage which is used in mating to grasp a female from behind and prise open her carapace and insert a spermatheca and thus fertilise the eggs. These fertilised eggs are termed winter eggs and are provided with extra shell layer called ephippium. The extra layer preserves and protects the egg inside from harsh environmental conditions until the more favourable times, such as spring, when the reproductive cycle is able to take place once again.?


    Daphnia magna with eggs

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    Resting egg pouch (ephippium) and the juvenile Daphnid that just hatched from it.

    [​IMG]

    The populations of several water flea species are considered threatened. The following are listed as vulnerable: Daphnia nivalis, Daphnia coronata, Daphnia occidentalis, and Daphnia jollyi.

    I found this interesting:

    ?A few Daphnia prey on tiny crustaceans and rotifers, but most are filter feeders, ingesting mainly unicellular algae and 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 trapped food particles are formed into a food bolus which then moves down the digestive tract until voided through the anus located on the ventral surface of the terminal appendage. 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 action of this second set of antennae is responsible for the jumping motion.?

    Daphnia may also be used to clear unwanted algae from fish tanks, provided they are not eaten by the fish.
    Many species of Daphnia are used in aquatic toxicology. As experimental animals they have many advantages being simple to produce in large numbers and exhibiting consistent responses to toxins.
    Daphnia is considered an indicator species or sentinel species which is an indicator of ecosystem health.

    This is the one species I found and still have to identify

    [​IMG]




    Refrence:

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    Kind regards
     
    Last edited by a moderator: Apr 11, 2014
  2. R.C.
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    R.C. Moderator Staff Member

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    Hi, Peter.

    Thanks for your time and effort in compiling this post.
     
  3. Andre
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    Andre Green fingers

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    Thanks Peter

    Very useful information!
     

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