Simulation of material circulation for a closed experiment using CEEF consisting of a plant and human system was performed. An initial set of materials that is necessary for CEEF to start its operation is determined by a decision procedure. Before the closure of the plant system (CPEF) which is operated independently, gas exchange of O₂ and CO₂ must be made between the inside and outside of the system. After the closure of the plant and human systems being operated in a cooperation mode where the materials are mutually exchanged, the exchange of the materials is no longer needed. The closure time is found to be equal to cultivation period of the largest amount of biomass among species to be cultivated in CPEF.

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As a food supply system for the future manned space activities, CERAS (Closed Ecological Recirculating Aquaculture System). containing phytoplankton, zooplankton and tilapia, Oreochlomis niloticus, has been studied. The system is relatively large and a large amount of energy will be consumed for the food production. However for use in space stations or developing stage of Luna-base, small and low-energy system will be requested. Accordingly, to establish the compact fish-culturing system, removal of zooplanktons from CERAS is expected.
It was known that tilapia fry feeds selectively zooplanktons. Subsequently possibility of culturing tilapia fry using only phytoplankton as diet must be studied. As the first step, we were examined survival rate of the fries that fed Chlorella vulgaris. It was no remarkable difference to the survival rate of the fries that took no food. Whereas in the following experiments the fries that fed Spirulina platensis or Euglena gracilis instead of Chlorella survived as well as the fries cultured with commercial diet. So it was suggested Spirulina and Euglena are suitable for diet of tilapia fry, and zooplanktons are not necessary to the tilapia culturing system.

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Phosphorus form and mineral budgets in the fish-rearing closed tank during a long-term (189 days) experiment with tilapia were evaluated. Besides phosphorus (P), other minerals examined were calcium (Ca), magnesium (Mg), potassium (K), iron (Fe). manganese (Mg), zinc (Zn) and copper (Cu). Among the elements excreted by tilapia, the main part of Mg and K were accumulated in the rearing-water, while others like, P, Ca, Fe, Mn, Zn and Cu were deposited and removed as solid wastes. Over 80% of P in the removal solids bound Ca (apatite-P) and another forms of P (non-apatite inorganic P and organic P) were negligible compared with fish diet This result shows that sedimentation of these minerals were regulated by the chemical equilibrium in this system.
In order to check if the generated mineral wastes could promote algal growth and effectively substitute for an algal culture medium, the amounts in the wastes were compared with the elemental composition of an algal culture medium used for Chlorella and Scenedesmus. Cu contents in rearing-water were enough to culture these microalgae. P, Fe, Mn and Zn contained in the removal solids are sufficient quantitatively, however, they cannot be used for algal culture directly, because they were insoluble precipitates, requiring ionization for their utilization. On the other hand, K and Mg contents were insufficient for algal culture. These results show that several elements in the wastes require ionization and/or supplementation, to serve as nutrients for algae in closed culture systems.

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Postural control in fish is mainly regulated by vestibular information under normal gravity conditions (1G). The aim of this study is to compare the ability of gravity sensations (i. e., vestibular function) in a food fish maintained at a lunar base or in a centrifuge rotor under microgravity. This experiment was conducted at low gravity (0.05G, 0.1G, and 0.2G) and under microgravity conditions to observe changes in the swimming behavior of juvenile tilapia, Oreochromis niloticus (TL 3-4cm) using a parabolic flight of an aircraft. The swimming behavior of the fish was similar under microgravity and at 0.05G conditions, indicating that their postural control depends on dorsal light response (i. e., visual information) rather than vestibular function. At 0.1G conditions about 40% of the fish showed normal swimming behavior when the direction of the light and gravity were same, demonstrating that both factors were helping the fish in controlling their posture. In contrast, 80% of the fish were oriented perpendicular to the direction of gravity, independent of the light direction under 0.2G condition. These results suggest that tilapia can sense gravity around 0.1G and their postural control depends on vestibular information at 0.2G.

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