摘要：1 - The quali-quantitative analysis of phytoplankton guild is usually carried out according to the method of Uthermöl (or sedimentation method), but in each step can be present a component of error that can affect the reliability of the final result, from sampling to data analysis. 2 - The following work is intended to focus attention on an important aspect of the phytoplankton analysis: the fixation, with the aim of assessing the effect of two chemical fixatives, formalin and Lugol’s solution, on the taxonomic composition and size structure of phytoplankton guilds. Accordingly, water samples were collected from three different water bodies, coastal marine area facing the Alimini Lake (Southern Adriatic Sea), transitional water (Alimini Grande Lake) and freshwater (Fontanelle Lake). The three water bodies are characterized by a different taxonomic structure of phytoplankton guilds due to difference in chemical-physical and hydrodynamic conditions. 3 - The samples were fixed and then analyzed according to a monthly time series for a period of 125 days. 4 - This study clearly shows that do not exist a better fixative, but on the basis of the phytoplankton classes observed in a sample we could prefer one of the two fixative
