The “Closed Equilibrated Biological Aquatic System” (C.E.B.A.S.) is originally dedicated to long-term multi-generation experiments with aquatic organisms in a space station (a national German option for the COLUMBUS module). The development of the laboratory prototype and the results of the international multidisriplinary zoological frame program was frequently presented at most space-relevant congresses and symposia since 1989. It consists of 3 components: 1. an aquatic animal tank with water recycling system (ZOOLOGICAL COMPONENT), 2. an aquatic higher plant chamber or microalgal bioreactor (BOTANICAL COMPONENT) and 3. a process control system (ELECTRONICAL COMPONENT). This system has a volume of approx. 100 liters was already successfully mid-term tested in its second and optimized version in which the BOTANICAL COMPONENT was filled with a rootless higher water plant. In addition, for spacelab or biosattelite experiments a MINI MODULE of the C.E.B.A.S. system fitting into a spacelab middeck locker tray was developed and tested in parallel the second version of which exhibited a biological stability between fishes, higher water plants and microorganisms of more than 40 days as reported on the World Space Congress in 1992. In the same year a third and highly optimized version of the C.E.B.A.S.-MINI MODULE was elaborated and tested from december 1992 until march 1993. As its precursors it has a total volume of about 11 liters and consists of the following subcomponents: main animal tank, bacteria filter, coarse filter, plant chamber and second “small animal” chamber. The water is driven through the system by a rotatory pump, the main animal tank and the plant chamber are illuminated by 4 W fluorescent lamps (adjustable for the latter). For emergency cases, a gas exchanger is inactively positioned in a closed side loop. A simple data acquisition is permanently monitoring pH-value, redox potential, pressure, temperature and oxygen saturation.During the experiment all relevant ions and the water hardness were determined chemically in daily intervals. The photoperiod of the main animal tank was 12 : 12 hours the plants were permanently illuminated. The agreed experimental animals of the international C.E.B.A.S. scientific frame program were utilized: the ovopviviparous teleost fish species Xiphophorus helleri and the pulmonate water snail Biomphalaria glabrata. As in all preliminary system tests a tropical rootless Ceratophyllum species served as experimental plant So, the MINI MODULE consists of the same components as the original system: ZOOLOGICAL COMPONENT, BOTANICAL COMPONENT and ELECTRONICAL COMPONENT. The only modifications are the 1 : 12 scaled-down volume and the minimized data acquisition/process control system. The paper presents the hardware design and detailedly the physical, chemical and biological data of the mid-term test. It has to be pointed out, moreover, that the C.E.B.A.S. system in general represents an artificial (man-made) aquatic ecosystem and that the results of the test of the third version of the C.E.B.A.S. MINI MODULE -including first microbiological investigations on the filter systems- allows an initial approach to an ecological system analysis with well-defined parameters. This contributes novel aspects for the development of innovative systems for combined aquacultural production methods for animal and plant biomasses as well for terrestrial utilization as for components of lunar or planetary base bioregenrative life support systems. The latter aspect will be critically analyzed from different points of view. Besides of these futuristic contemplations, however, the basic evaluation of this test shows clearly that the C.E.B.A.S.-MINI MODULE is more than suitable for mid-term spacelab or biosattelite missions up to a minimum of 8 weeks. Therefore the spaceflight hardware of a spacelab middeck locher version of the C.E.B.A.S. MINI MODULE went into industrial construction in june 1993 by order of the German Space Agency (DARA).