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カダヤシの塩分の上昇に対する馴致
伊藤 寿茂（新江ノ島水族館）

ABSTRACT. The salinity tolerance of the mosquito-fish Gambusia affinis that is naturalized to Japan was investigated in tanks. The salinity of water in the tanks was raised at various rates, and the percentage of fish that survived the increase in salinity was investigated. In the tank in which the salinity was raised to the sea water concentration (35 psu) within a 24-h period, almost all individuals (more than 90%) died. However, when the salinity was gradually raised over a period of three days or more, almost all individuals survived. Thus, it was shown that the mosquito-fish can survive in sea water. Furthermore, the possibility of migration of the mosquito-fish to other geographical areas via the sea was also considered.


摘要　日本に帰化した淡水魚カダヤシ Gambusia affinis の塩分耐性を水槽内で調べた．飼育水の塩分を様々な上昇幅で24時間毎に上げていき，その生残率を調べた．1日で海水濃度まで上げた水槽では，殆どの個体が死亡したが，3日以上かけて徐々に塩分を上げた水槽では，その生残率は大幅に高まり，海水に高い適応性のある魚種であることが確認できた．カダヤシは汽水域や海水域を一時的に生活場所と出来，海水域を介して分布を拡大する可能性が示された．