Abramiuk I. Structure of ichthyoplankton in small plain rivers

The work highlights the patterns of structural changes in early young fish communities during spring-summer season in small plain rivers with different character of channel transformation. It has been established that in a river with a transformed channel the species richness and diversity of ichthyoplankton is lower than in a river with a relatively natural channel. The ichthyoplankton structure was constantly changing during the season due to different spawning periods of breeders. The downstream migration of young fish was characteristic for the studied rivers, which occurred even under regulation of the channel. It has been established that the ability of young fish to counteract the flow depends on its body shape, it defines the transition limit from planktonic to nektonic phase of existence.