Toxigenic cyanophyta (Cyanobacteria) are found in eutrophied waters in many countries around the world. Many species of Cyanobacteria produce a wide range of toxins which during the decomposition of blooms are often the main cause of increased number of diseases and higher mortality among aquatic animals. Several studies have shown that cyanotoxins (e.g. microcystins), are able to modulate the activity of immune cells of vertebrates. However, the effect of cyanotoxins as natural water contaminant on immune system of fish still needs elucidation. The objective of this review is to summarise and evaluate data on immunotoxicity of cyanotoxins to fish available in the literature and results from our studies.