Within the project “Development of evidence-based recommendations for increasing the fish productivity of fishery reservoirs through the introduction and reintroduction of fish and hydrobionts – components of the food base of fish” of the program «Complete assessment of the state of fish resources and other hydrobionts of the main fishing water reservoirs of Kazakhstan and the development of evidence-based recommendations for their sustainable use» employees of the laboratory of hydrobiology and hydroanalysts are testing the survival of polychaete worms Hediste divesicolor (O.F. Müller, 1776) of the Aral Sea in natural water with different mineralization.