The aim of this dissertation thesis was to ascertain the effects of a substances which are used or can be used in fisheries. The first group of tested substances were algaecides, the most common tool used for algae and cyanobacteria elimination. The second group consists of organic pigments, which can be used for fish mass-marking from early stages. The selection of the test organism for the toxicity tests was performed to represent the individual trophic levels of aquatic ecosystems: primary producers, zooplankton and fish. For acute toxicity tests and inhibition tests were used these algaecides: Guanicide, Pelargonic Acid, Polyaluminiumchloride (PAX 18), Polyhexamethylene Guanidine (PHMG), and Terbutryn. For the organic dyes testing was selected fluorescent dye Alizarin Red S and Alizarin Complexone. Algaecides were used in inhibition tests for green algae (Desmodesmus communis, Parachlorella kessleri) and cyanobacteria (Anabaena sp.), in immobilization test for zooplankton (Daphnia magna) and acute tests for fish (Danio rerio). The organic dyes were tested on fish for determination of effective and safe concentration.