報告書番号

U90042

タイトル（和文）

高能率魚類生産のための水質浄化技術の開発５．ヒラメの長期飼育時における水質変化

タイトル（英文）

DEVELOPMENT OF WATER PURIFICATION TECHNOLOGIES FOR INTENSIVE FISH CULTURE. 5.CHEMICAL CHANGES IN CULTURE WATER OF RECIRCULATING FISH- CULTURE SYSTEMS FOR JAPANESE FLOUNDER,PARALICHTHYS OLIVACEUS.

概要 （図表や脚注は「報告書全文」に掲載しております）

循環濾過養魚システムのための水質管理技術を開発するには，飼育が長期にわたる場合に飼育水に蓄積または欠乏する物質を明らかにし，対応策を考える必要がある。そこで，総水量約４ｍ３の循環濾過水槽を用い，ヒラメを種苗から４００ｇサイズまで約１１ヶ月間，高密度で飼育して，飼育水の水質変化を調べた。飼育水には，餌起源の窒素とリンが，主に硝酸，リン酸として蓄積した。硝酸は給餌量に比例して増加したが，リン酸は３０～４０ｍｇＰＯ４－Ｐ／ｌ以上になると海水中のカルシウム，マグネシウムと沈殿して除去されることがわかった。硝酸，リン酸の蓄積に伴うｐＨの低下は，炭酸水素ナトリウム溶液を添加して防いだ。また，飼育の経過と共に溶存有機物が蓄積し，飼育水が黄褐色化した。本実験の水質変化の範囲内では，魚の生育に影響は見られなかったが，飼育水を長期間利用するには，飼育の経過と共に増加する硝酸，有機物の除去などを行う必要がある

概要 （英文）

TO DEVELOP WATER-QUALITY CONTROL TECHNIQUE FOR CLOSED RECIRCULATING FISH-CULTURE SYSTEMS,THE CHEMICAL CHANGES IN THE CULTURE WATER WERE STUDIED DURING LONG-TERM REARING EXPERIMENTS ON THE JAPANESE FLOUNDER. A CLOSED RECIRCULATING FISH-CULTURE SYSTEM WITH A TOTAL WATER VOLUME OF 4.5 M3 WAS OPERATED FOR 11 MONTHS. THERE WERE CONSIDERABLE FLUCTUATIONS IN WATER QUALITY DURING THE EARLY CULTIVATION STAGES. HOWEVER,THE VARIATIONS BECAME STABLE AFTER 2 MONTHS. NITRATE AND PHOSPHATE LEVELS IN THE CULTURE WATER REACHED 305 MGNO3-N/L AND 25 MGPO4-P/L AT THE END OF CULTURING. THE ACCUMULATED NITROGEN AND PHOSPHORUS IN THE CULTURE WATER ACCOUNTED FOR 43% AND 13% OF THE ELEMENTS ADDED ASFOOD,RESPECTIVELY. WHILE NITRATE IN THE CULTURE WATER TENDED TO INCREASE WITH THE CUMULATIVE AMOUNT OF FOOD,THE PHOSPHATE LEVEL STABILIZED ASTHE WATER AGED. THE PHOSPHATE LEVEL IN THE CULTURE WATER RARELY EXCEEDED 30-40 MGPO4-P/L AS A RESULT OF PRECIPITATION BY CALCIUM AND MAGNESIUM IONS. THE WATER ACIDIFICATION ASSOCIATED WITH NITRATE AND PHOSPHATE ACCUMULATION WAS CONTROLLED BY ADDITION OF NAHCO3 SOLUTION. DISSOLVED ORGANIC MATTER ALSO ACCUMULATED IN THE CULTURE WATER AT A CONCENTRATION OF 56 MGC/L. THE WATER BECAME YELLOW-BROWN DUE TO THE ACCUMULATION OF THIS ORGANIC MATTER. ALTHOUGH THE CHANGES IN WATER QUALITY HAD NO SIGNIFICANT EFFECTS ON FISH GROWTH,NITRATE AND DISSOLVED ORGANIC MATTER INCREASE LINEARLY WITH TIME AND MUST BE REMOVED FOR LONG-TERM OPERATION OF A CLOSED CULTURE SYSTEM.

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