The invention relates to a method of producing Artemia offspring in which the reproducing Artemia are kept in an aqua-culture and the offspring are harvested.
This method is known and as far as the production of cysts is concerned it is described in the article "Controlled production of Artemia cysts in batch cultures" by D. Versichele and P. Sorgeloos in the book "Brine Shrimp Artemia", Vol. 3, "Ecology culturing use in aqua-culture", authors: G. Persoone, P. Sorgeloos, O. Roels and E. Jaspers, page 231 to 246, Universa Press, Wetteren, Belgium.
Artemia, the brine shrimp, is found restrictively in salt lakes throughout the world. Due to the extreme ecologic conditions in these biotopes, for example, a salinity of more than 100 gs per liter of water, predators and food competitors of Artemia are lacking, and the Artemia can flourish in these biotopes. As a result of varying environmental conditions, for example, drying up of the salt lake, the manner of reproduction changes in a sense such that the reproduction changes from an ovoviviparous reproduction (living offspring) into an oviparous reproduction (inactive offspring). As living offspring nauplii are produced which grow up to adult Artemia within 9 days to 6 weeks (depending on the culture conditions). In the case of the oviparous reproduction the embryonic development is reversibly discontinued during gastrulation. Each gastrula is surrounded by a sheel impregnated with a heamatine-like substance. These encapsulated gastrulae are termed cysts, which are excreted in the water. The cysts remain floating in the salt water and subsequently are washed on the shore. After processing, the cysts can be dried or kept under anaerobic conditions for many years. After the cysts are again placed in sea water the metabolism of the embryo is activated and after a few hours a free-swimming nauplius is set free of the cyst.
Artemia nauplii are used as food for the larvae of fish and crustacea. Because Artemia cysts can be kept for a long time and free-swimming nauplii become available a few hours after introduction of the cysts into salt water by expansion of the cysts, Artemia cysts constitute an ideal source of food for larvae of fish or crustacea.
However, the production of Artemia offspring in nature is too low to meet the need. Apart therefrom Artemia offspring produced in nature have the disadvantage that they may be contaminated by any kind of toxic compound, for example chlorinated hydrocarbons.
Scientific tests revealed that the batch culture production of one type of offspring on a technical scale is not feasible, since the batch culture production of Artemia offspring has the drawback that due to pollution, for example, by faeces, metabolites, peeling and bacteria, the water quality is deteriorated so that the batch culture has to be refreshed each week, even in the case in which the offspring producing Artemia is kept at low density in the batch culture. However, a low density of Artemia results in a low production per cubic meter and a low degree of usefulness of the food added to the batch culture. Due to the necessarily low density of Artemia in a batch culture the volume in which the Artemia are swimming is smaller than the overall volume of the batch culture, which means that only part of the total volume is populated by the Artemia. On the one hand this means that the food present in the unpopulated volume, remains unused (the degree of use of the available food is, therefore, low) and on the other hand it means that the quantity of food in the populated volume has to meet the daily need.