The paper presents the analysis of structure of fish communities in five small postexcavation reservoirs situated in Tyśmienica valley (Polesie Lubelskie). Special attention was paid to the quality of population of lake minnow Eupallasella percnurus. By the time the extensive drainage works were done in the 60s and 70s of the 20th century, Polesie Lubelskie was rich in small water reservoirs. As a result of drainage of wetlands, many of them disappeared. Among those which still exist, most of them are located in the Tyśmienica valley. The study revealed that the studied reservoir inhabited seven fish species representing two families. It was also found that structure of dominance and biomass structure is very diverse. In each reservoir the dominant species was different. The lake minnow E. percnurus was determined in three reservoires.

Structure of fish communities of five small water reservoirs located near the Wieprz--Krzna Canal was investigated during the years 2002, 2008 and 2014. In the analyzed water bod-ies seven fish were noted, representing four families: Cyprinidae (5 species) and Esocidae, Cobi-tidae and Ictaluridae (1 species each). In the structure of collected fish two protected species (M. fossilis and R. sericeus amarus) and one alien species (C. auratus gibelio) were presented. Domination structure of ichthyofauna showed considerable differences. Among the dominant species were: I. nebulosus (all five reservoir), C. auratus (Jabłoń Center 2, Jabłoń Church and Jabłoń Firlej-Ostrówek), and R. rutilus (Jabłoń West and Jabłoń Firlej-Ostrówek). The percentage of each fish species in the biomass was slightly different in relation to the structure of domination expressed by the number of identified individuals. Regardless of the reservoir, larger share held: E. lucius, I. nebulosus and C. auratus Moreover, one of the purpose of the study was searching for a new stands of lake minnow. However, the species was not recorded in fish communities of any of the reservoirs, despite of the ecological state of reservoirs indicating the potential habitat for lake minnow.