ヒラソウダの人工ふ化と仔魚飼育について

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[Author abstract]Some trials of artificial fertilization and rearing of larvae in Auxis thazard (hirasoda in Japanese) were made in 1972. The authors made some trials of aritficial fertilization of this fish aboard some professional fishing vessels during the spawning season of the fish (May～July). The mature fish were caught on May 30 and June 16 and 25, 1972 by a trap net set near the coast of Oshima Island near Cape Shionomisaki. About 70 thousand ripe eggs were obtained from the fish and fertilized in dry method. The fertilized eggs are buoyant, spherical and 0.93 to 0.98 mm in diameter. The fertilized eggs were then transported from Oshima to the Shirahama Fisheries Laboratory of the Kinki University, Wakayama Prefecture and kept there in cylindrical tanks of 0.03 to 70 tons. The eggs hatched out in 34 to 62 hours at the water temperature ranging from 21.4 to 23.5°C. The newly hatched larvae measured 3.26 to 3.60 mm in total length. The larvae were fed three days after hatching with a kind of rotifer previously cultivated, which was replaced 7 days after hatching by the second food, several kinds of marine zoo-plankton, and these were then replaced about 20 days after hatching by the third food, several kinds of minced fish. Under best conditions, the larvae grew up to 64 mm in total length in 17 days, and to 120 mm in 33 days after hatching, but failed to attain further stages. Stages up to 120 mm in total length are shown in Plates 1 and 2.[著者抄録]1. 1972年5月から7月までの間、和歌山県串本町大島樫野定置網から漁獲されるヒラソウダから採卵･人工授精を行ない、授精卵を同県白浜町本学水産研究所へ輸送し、ふ化および仔魚の飼育実験を行なった。2. .紀伊半島南部の沿岸に 5～6月(水温18～22 ℃)に来遊するヒラソウダから熟卵が採取され、人工授精･ふ化ができることが明らかとなった。3. 卵は直径0.93～0.98mmの分離浮性で1個の油球を持ち、水温 21.4～23.5℃で30～54時間でふ化した。4. 仔魚は培養したシオミズツボワムシ･天然海産プランクトン･小魚のミンチなどを摂取して成育し、ふ化当日0.34mmの仔魚は、小型水槽では20日29mm、30日56mm、36日60mmに成長したが、大型水槽では17日64mm、33日120mmに成長した。5. 本実験の結果、ヒラソウダの採卵･人工ふ化および仔魚から若魚までの飼育が可能なことが実証され、マグロ頬の人工ふ化･仔魚飼育研究上参考となると思われる知見が得られた。
1973-03-15

ヒラソウダの人工ふ化と仔魚飼育について

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