Reproductive Cycle and Parasites Infection in the Neptune Whelk Neptunea arthritica in Lagoon Saroma

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  • KAWAI Kei
    Laboratory of Mariculture, Faculty of Fisheries, Hokkaido University
  • YAMAGUCHI Shiori
    Laboratory of Mariculture, Faculty of Fisheries, Hokkaido University
  • IDE Nahomu
    Laboratory of Mariculture, Faculty of Fisheries, Hokkaido University
  • GOSHIMA Seiji
    Laboratory of Mariculture, Faculty of Fisheries, Hokkaido University
  • NAKAO Shigeru
    Laboratory of Mariculture, Faculty of Fisheries, Hokkaido University

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Other Title
  • サロマ湖産ヒメエゾボラの生殖周期
  • サロマ湖産ヒメエゾボラの生殖周期〔英文〕
  • サロマコサン ヒメエゾボラ ノ セイショク シュウキ エイブン

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Reproduction was studied for the neptune whelk Neptunea arthritica in Lagoon Saroma. Fishery of the whelk has been prohibited in the lagoon since 1986 because of depleting resource, however, only few egg masses were observed. Histological examination and gonado-somatic index (GSI) showed the distinct annual reproductive cycle. The cycle is as follows : in ovaries, recovery period (Aug.-Nov.), growing period (Oct.-Apr.), mature period (Apr.-July) and spent period (May-Aug.) : in testes, recovery period (Apr.-May), growing period (Apr.-July), mature period (Aug.-Dec.) and spent period (Nov.-Apr.) : in seminal vesicles, resting period (July-Aug.), accumulating period (Sep.-Apr.) and spent period (Apr.-June). Copulating and spawning periods were from April to August and from May to August, respectively. Whelks infected by digenean trematodes were observed in the lagoon. GSI and histological feature in infected and uninfected females were different. Infected females could not develop the ovaries. Infected males also showed lower values in both testis and seminal vesicle indexes, although their annual trends were similar to that of uninfected males. Influence of parasites on the females was stronger than on the males. Because the infection rate of the whole area was very low and GSI value was high even after spawning time in the place where infection rate was low, infection of parasites was not the main factor which prevented the neptune whelk from spawning in the lagoon.

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