Features of the species composition and structure of fish communities in small anthropogenic reservoirs with different content of dissolved mineral nitrogen

In 22 small anthropogenic reservoirs with an area of 0.4 to 62 ha located in the territory of the Udmurt Republic, individuals of different fish species were captured and water samples were taken in late spring for analysis of NO3–, NO2– and NH4+ content. In many reservoirs, concentrations of ammonium exceed the maximum permissible according to the fishing standards for water quality, and in some this is also the case with nitrites. Ponds with zooplanktophages (bleak Alburnus alburnus (L.) and belica Leucaspius delineates (Heckel)) present in fish communities were statistically significantly different in the increased content of total dissolved mineral nitrogen from reservoirs where these two fish species were not registered. In perch and roach reservoirs, the numerical proportion of river perch Perca fluviatilis was negatively and statistically significantly related to the level of their contamination with nitrogen ionic forms.