Cyanobacteria are grouped together with phytoplankton as primary producers
in aquatic environments. These organisms are very diverse and under favorable
conditions, their biomass increases dramatically, leading to blooms. Cyanobacterial
blooms in aquatic environments are a well known global phenomenon, largely as a
result of anthropogenic pressures, such as increas-ing nutrient inputs from catchment
areas or climate change. Especially, planktonic cyanobacteria can thrive in surface
waters and cause several adverse effects on aquatic organisms due to variations in pH,
blocking light from entering the water and oxygen deficiency as a result of respiration
at night. Moreover, they also produce toxins, called cyanotoxins, which can pose
harmful effects on organisms in every trophic level; phytoplankton, zooplankton,
invertebrates, fish, birds and also mammals. Cyanotoxins comprise of very diverse
chemical compounds with several adverse effects on organisms. Considering the
diversity of cyanotoxins, we chose two cyanotoxins, microcystin and
cylindrospermopsin, since there are relatively more data about their toxic effects on
fish, and also the former has a worldwide distribution and the latter is an emerging
toxin with an extending geographical range. Together with the other adverse effects on
fish, microcystins and cylindrospermopsin could cause oxidative stress and
histopathological changes which we focus on and review in detail in this chapter.
Keywords: Cyanobacteria, Cylindrospermopsin, Fish, Histopathology,
Microcystin, Oxidative stress.
