In 2019, during spring flood, we collected unusual Lampetra fluviatilis smolts migrating from a small lake, as part of a multi-year survey in the Chernaya River (Gulf of Finland, Baltic Sea). They differed from the ordinary Lampetra fluviatilis individuals in some of the features, mainly size. The emigration occurred at the darkest period of night and during extreme flooding, which significantly worsened the conditions in the Lake Gladyshevskoe and Chernaya River. In these individuals, lacus smolts, emigration occurred in the spring season with the migration of ordinary flumen specimens. Several hypotheses are discussed to explain the observation of large lacus (148–165 mm) individuals: they are seaward migrants, within expected body sizes of European river lamprey species but unusual for Gulf of Finland tributaries; the lake is a transitional habitat, and the postmetamorphic lacus juveniles migrating through it from a tributary; postmetamorphic lacus juveniles spend some time feeding in a lake but emigrated due to environmental conditions; larvae of European river lamprey, developing in the eutrophic lake, reach greater sizes than riverine larvae before transformation and subsequently produce larger juveniles.

2019 年春季洪水期间，我们在切尔纳亚河（芬兰湾，波罗的海）进行了一项多年调查，收集了从一个小湖迁徙而来的不寻常的兰佩特拉河豚鱼。它们在某些特征（主要是大小）上与普通的兰佩特拉河豚个体不同。移民发生在最黑暗的夜晚和极端洪水期间，这大大恶化了格拉迪雪夫斯科湖和切尔纳亚河的状况。在这些个体中，小鲑鱼在春季随普通水流标本的迁徙而迁徙。讨论了几个假设来解释大湖的观察（148-165 毫米）个体：它们是向海移民，在欧洲河七鳃鳗物种的预期体型范围内，但在芬兰湾支流中不常见；该湖是一个过渡性栖息地，变质后的幼鱼从一条支流穿过该湖；变质后的幼鱼会在湖中觅食一段时间，但由于环境条件而迁移；欧洲河七鳃鳗的幼虫在富营养化的湖泊中发育，比转化前的河流幼虫体型更大，随后产生更大的幼体。