BASIC STUDIES ON THE DEVELOPMENT OF CLOSED ECOLOGICAL RE CIRCULATING AQUATIC ANIMAL CULTURE SYSTEMS

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A closed ecological recirculating aquaculture system(CERAS), a part of the models of a controlled ecological life support system(CELSS), was developed in the hydrosphere for aquatic organisms such as phytoplankton, zooplankton and fish. Using a fish-rearing closed tank(air-tight tanks)with an O_2/CO_2 exchange unit, the influence of different photoperiod cycles(3L : 3D ; 6L : 6D ; 12L : 12D ; ＆ 24L : 24D)on the metabolic rate and energy loss of young and adult tilapia Oreochromis niloticus was investigated. This study suggested that energy conservation would be possible if this fish is exposed to longer cycles of photoperiod rather that shorter ones. Resting respiratory rate of young tilapia was higher than that of adult one. In this closed system, tilapia showed normal growth and high feed efficiency compared with the recirculating open tank under a high concentration of NO_3-N over the 189-day period. Phosphorus form and mineral budgets in the fish-rearing closed tank during a long term experiment with tilapia were also evaluated. Several elements in the wastes require ionization and /or supplement, to serve as nutrients for alga in closed culture systems. Tilapia can be cultured only Spirulina platensis from larvae to adult. This results suggest that it is feasible to construct a food chain using raw Spirulina to feed tilapia from the onset of exogenous feeding in a CERAS.Finally, the effects of CO_2 and O_2 concentrations and light intensity on growth of microalgae Euglena gracilis were investigated. The multiplication rate of cells was highest and the cell number increased by 8.3 times during 48h under a condition of 4% CO_<>, 21% O_2 and 100μ moll m^<-2>s^<-1> PPF.This study obtained many basic and useful informations to develop CERAS.