| Budget Amount *help |
¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1993: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Research Abstract |
This study has begun to clarify the natural inducers for larval settlement and metamorphosis of the abalone Haliotis spp. However, because of the limited hatching season for the abalone, the subtropical gastropod Trochus niloticus, whose hatching season is different from that of Haliotis spp., was also tested. After many trials we finally established a bioassay for this purpose as follows : 1) Sample solution (about 5-300 mul) was added into a flat bottom glass test tube(phi2.5 x 15cm). 2) After evaporating the solvent was added 35 ml of autoclaved sea water containing 150 mg/l each of streptomycin sulfate and penicillin G potassium. 3) About ten larvae were introduced and each larvae was microscopically observed after 1-8 days.
First we tested gamma-Aminobutyric acid (GABA) and MeOH extract of the coralline red alga Lithophyllum okamurae for metamorphosis of the top shell T.niloticus. This study was the first chemical study on larval metamorphosis of T.niloticus. The algal extract indu
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ced larval metamorphosis (about 80%) at doses of the extracts equivalent to 5-15 mg of the air-dried alga. GABA also induced the metamorphosis at 10^<-5--3>M.The mode of action was clearly different from each other [Nippon Suisan Gakkaishi, 59, 1261 (1993)]. The algal active principle was found to be eluted in less polar fractions than polyunsaturated fatty acids, some of which have been reported to induce metamorphosis of some Haliotis and some tube worm larvae. Frequent typhoon attacks caused troubles in obtaining the larvae for the test, resulting in incompletion of the isolation of the active principle(s).
The less polar fractions from the algal extract was found to induce the metamorphosis of H.discus and H.sieboldi. Because of limited numbers of bioassay, isolation of the active principle(s) has not been finished and is to be waited till next season.
GABA was, for the first time, shown to metamorphose the larvae of H.discus and H.sieboldi, although no effect on H.diversicolor aqutilis. One of us(Akutsu) has got experimental results for a successful application of GABA to seedling production of the abalones. Less
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