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A New concept of a life support system for aquatic animals using the miniaquarium Tech­nic.  M. Franz¹, S. Bцser², N. Hiesgen¹, E. Horn², U. Kьbler¹, S. Lдmmlein³, and A. Schwarzwдlder¹. ¹EADS Space Transportation, Fried­richshafen, Germany; ²Gravitational Physiology, University, Ulm, Germany; ³University of Applied Sciences, Regensburg, Germany.

   The miniaquarium was successfully used during two space missions (STS-84, 1997; Soyuz taxi flight Andromиde, 2001) to expose Xenopus leavis tadpoles to microgravity. So far, its use is limited to early developmental stages and to a flight period of up to 10 days. This is the period of life during which feeding is not necessary because the embryos have enough yolk to survive. The use of older stages and longer flight periods needs an additional unit to clean the water and feed the organisms (cf. Sebastian et al., Acta Astronautica 42:419-430, 1998). A system has been developed by which tadpoles survive for at least 1 month at a high percentage up to stage 56. It includes (1) a mechanical cleaning device made of cotton and foam filters and (2) a biological conversion of ammonium/ammoniac-compounds (NH₃/NH₄⁺) to nitrite (N0₂^-) and finally to nitrate (NO₃^-) using nitrifying bacteria. In the last cleaning step (3) the mentioned toxic compounds are removed and stored by highly effective absorber materials. The system can be used in a dark environment, because no plants are needed. A closed circular water flow is produced by a miniaturised peristaltic pump. After the clarification process a liquid and suitable food is added. This arrangement was tested several times. Survival rates of up to 85% were reached.
   A prototype has been built in which liquid food is introduced into the system using an osmotic pump. It is filled once and provides the aquarium with food at a constant rate between 2 to 10 weeks, depending of the pump model. No crew interaction is needed. This supply unit developed for the miniaquarium system can be used for Xenopus laevis and other aquatic organisms.