ハマグリ産卵期の研究I.昭和22年東京灣に於けるハマグリ産卵期
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概要
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The spawning season of Meretrix luzoria has been investigated by a number of authors for a long time at various localities with the purpose of protecting the adult cleam during the spawning season and finding out the gathering time of the clam seeds. The ivestigation of clam in Tokyo Bay was intended in consecutive years in order to determine appropriately its spawning season and to make clear the decisive environmental factors to the spawning because the irregular results have been obtained by the previous authors. The material was supplied by the courtesy of Tokyo and Chiba Fishries Experimental Stations collected from their clam fields. In Haneda clam filed the ejculation was begun early in June and reached its highest season in July and became active again during the time from middle of August to that of September and seemed to last by late in October. The temperature and the specific gravity of sea water were 20°-30°C and about 1.010 at the ejaculating season in its height respectively. The temperature registered 15° and the specific gravity of sea water was 1.006 at about end of ejaculation. Since the heavy typhoon of September 15 th the sea was covered by water of the River Tama for several days and its specific gravity decreased nearly to a value of freshwater. The sudden decrease of specific gravity of sea water may have effect intensively on the discharging activity of clams. The spawning was begun from early in June and reached peak in July and active from middle of August to early in September and seemed to finish at about end of September or early in October. The temperature and the specific gravity of sea water at the highest season of spawning were the same as in the ejaculation of male. The highest spawning season in Haneda was in accord nearly with that in Chiba, investigated by Naito in 1930. The male clam of Chiba began to discharge sperms from early in June and the time from middle of June to early in August was the ejaculating season at its height and the clam was active again at about early and middle in September and ceased its discharge at about end of September. The temperature was 20°-30° and the specific gravity of sea water was 1.02-1.024 at the highest season of ejaculation. At this time there was no great diversity of temperature in both localities but the specific gravity in Chiba was exceedingly higher than that in Haneda where seemed to be much affected by river water of the Tama. The temperature and the it sepcific gravity when the ejaculation ceased were both higher in Chiba than in Haneda. The clam began to spawn early in June and was active a little from late in June to middle of July and from late in July to early in August but the spawning reached at its peak in middle and late of August and active again in early and middle of September and ceased by end of October. The temperature ranged from 26° to 30° and the specific gravity of sea water from 1.018 to 1.019 at the highest season of spawning. Therefore the temperature in that season was higher than that in the ejaculation and in the spawning season at Hancda; the specific gravity in that season was a little lower than in the ejaculation and somewhat higher than in Haneda. The beginning and the highest seasons of ejaculation coincided at Chiba and Haneda. The ejaculation was prolonged much more at its peak in Chiba than in Haneda and ceased earlier in Chiba than in Haneda. Both the highest seasons of ejaculation and spawning were concurrently in Haneda but not so in Chiba. In Chiba the highest peak of spawning was retarded by a month in comparison with the results obtained by Naito in 1930 as in the case of oyster which was observed by Fujimori along the coast of Tokyo Bay in Chiba Prefecture in 1947. It is conceivable that there may be some factors delaying spawning season of clam and oyster along the Chiba coast of Tokyo Bay in 1947.
- 公益社団法人 日本水産学会の論文