Abstract: According to observations during the fertilization period,the posture structure of the Lampetra japonica (Marten) changes; the normally separate dorsal fins join so that they are adjacent. Systematic measurement of 116 Lampetra japonica (55 females, 61 males) have done. When the Lampertra japonicareturn to their spawning area up the river from the Sea of Japan in three different groups during different seasons, 27 different measurements were conducted on each fish. Each spawning group brought into comparison from t-test analyses and dissected Lampetra japonica on site in order to observe their posture structure. From the time the Lampetra japonica enter the freshwater river until spring of the following year when the eggs are released, especially during the fertilization period, various aspects of their body structure undergo change.

Key words: Lampetra japonica(Marten), double dorsal fins, measurements, t-test, change of posture

摘要： 为进一步揭示日本七鳃鳗由以两背鳍相分离为特征的非产卵态体型变为产卵时(含产后)两背鳍相连接的产卵态体型这一体态变型现象，选取了27项体态特征可量性状，对从日本海回归 内河的日本七鳃鳗性成熟产卵群体不同时季3种类群共116尾(♀♀55，♂♂61)标本进行了系 统测量。对每一性状均用统计处理数据按类群分雌雄进行了统计学差异显著性检验对比，从而揭示出了日本七鳃鳗溯入内河时至翌春产卵前特别是产卵活动体态变型时躯体各部位具体 的变化情形。

关键词: 日本七鳃鳗, 两背鳍, 可量性状, t检验, 体态变型