Abstract: As the only intermediate host of schistosome, snails generally live at the bottomland of lakes. The vertical migration of snails on the bottomland is closely related to the water level but usually delayed to the water level alteration, which has not yet been considered in previous studies. As a result, the snails’ vertical migration is always difficult to describe or predict accurately. A generalized model for the changes of snails’ vertical distribution was proposed in this study, and a calculation method is developed for predicting the theoretical distribution elevation of snails in the presence of altered water level. The calculation method reveals that 1). the elevation at which snails are distributed increases with the rise of water level and decreases with the decline of water level; 2). the distance between the snail distribution elevation and the water level decreases with the rising of water level, and increases with the descending of water level. According to the field data at the Dongkou bottomland of Dongting Lake, the calculation method based on the delayed response for predicting the snails’ distribution elevation was tested, and the results showed that the relationship between the snails’ vertical distribution and the water level alteration established in this paper can be used to accurately predict the snails’ distribution elevation.

Key words: snail, zonal distribution, vertical migration, water level, delayed response