| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1987: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1986: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
Maintenance of the quality of water is a serious problem in the culture of aquatic organisms. Culture water becomes polluted by excreta and excess feed, resulting in an increase of ammonia. The ammonia may be decreased by a recirculating water filtering system. With time, however, the water tends to show a low PH due to an increase in the anions, nitrite, nitrate, phosphate and silicate. Studies were made to determine the influeces of several filter materials on the quality of the water in closed water culture systems.
The experimental aquaria were made of glass with plastic frame with bottom filtering systems. The filter materials used were glass ball, pebble, acryl granule, coral, and saran net. The fish were fed a crumble diet ad libitum and were kept in the aquaria for about 2-5 months. Water was not changed during the experiment. Water circulation was controlled by constant recirculation of water to each aquaria.
PH in recirculated water with blass ball, pebble, acryl granule, and s
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aran net filters decreased with time to about pH 6. However, pH with coral filter was maintained at about 7.0-7.5 throughout the 2-5 months of the experiment. Alkalinity decreased and acidity increased with time in all aquaria, but with only a small decrease of alkalinity with the coral filter. Ammonia increased markedly at first, but decreased to low levels after. These low levels were maintained for about one month, followed by increases in ammonia except for the aquarium with the coral filter. Increases were smallest in the water with the pebble filter. Nitrite increased sharply during the first time and decreased after that in all aquaria. Nitrate, phosphate , silicate, calcium, and magnesium increased with time in all aquaria. The cations, calcium and magnesium, originated from the filter materials and the feed of fish.
These results clearly indicate that the quality in the recirculated water with coral filter had the following characteristics: PH is not changed, there was only a small decrease in alkalinity, and the nitrate level is maintained low after an initial small increase. Pebble filter may be effective during the first half month. On the other hand, glass ball, acryl granul, and saran net filtering systems appear to be inabequate for the culture of fresh water and sea water fish in a closed system. Less
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