Fish-Ciliate (Protista: Ciliophora) Interactions in Aquaculture: Symbiotic and Ecological Relations

The ciliates are the most homogeneous and the most diverse group of protists. Most ciliate species live free in marine, freshwater and terrestrial habitats. However, there are also those living as symbiont. The symbiotic species range from obligatory parasitism and commensalism to opportunistic facultative forms. As the ciliates directly cause disease in fish, they affect fish health indirectly through fish pathogens such as bacteria and fungi. In aquariums and fish farms with high fish population density, diseases caused by symbiotic ciliates also become widespread and cause significant losses. The interaction of the ciliates with the fish is not the only disease. They are important members of aquatic food web. And they also have the potential to be biological indicators in the evaluation of water quality in fish cultures. This review is intended to draw attention to the relationships between fish-ciliate and particularly to opportunistic pathogen ciliates, which are part of the symbiotic relationship