Protozoan infections in farmed fish from Brazil: diagnosis and pathogenesis.

The Phylum Protozoa brings together several organisms evolutionarily different that may act as ecto or endoparasites of fishes over the world being responsible for diseases, which, in turn, may lead to economical and social impacts in different countries. Apart from the recent advances for the diagnosis of fish diseases in Brazil, little is known on the protozoan parasites and their relationship with environment and host. This revision presents the most important protozoan parasites found in farmed fish from Brazil, not only with emphasis on its diagnosis, biology, transmission and host-parasite relationship, but also on some information that may be useful to researchers in determining the correct diagnosis in fish farms.