Ichtiofauna górnego odcinka Czarnej Hańczy (zlewnia Niemna, północno-wschodnia Polska)

The composition and structure of the ichthyofauna of the upper course of the Czarna Hańcza River (Nemen River basin northeast Poland) and changes in it since 1993 were studied. Fifteen fish species belonging to five reproduction ecology guilds were confirmed to occur currently in the river. The number of fish species occurring at given sites increased as the width of the river increased, while the share of rheophilous species increased with increasing river slope.