The authors investigated aquatic mycota growing on the muscles of 8 aquarium fish species in the water from five limnologically and trophically different water bodies (one spring, two rivers, one pond and one lake). All of these water bodies are strongly loaded in spring and in autumn. 50 species of aquatic mycota were found on the muscles of investigated aquarium fish. In autumn, 43 species were noted, while only 33 were observed in spring. In all the five reservoirs, oxidability, all nitrogen forms, phosphates and sulphates showed considerably higher values in spring, compared to autumn. Four such mycotic species Monoblepharis sphaerica, Aphanomyces invadans, Aphanomyces piscicida and Saprolegnia polymorpha were recorded for the first time from Poland.