A great number and diversity of animal species are capable of parasitizing fish, ranging from microscopic protozoan to grossly visible crustaceans and annelids. In the wild fish, there is large range of parasites but they are usually only present in small numbers, they can be considered a normal finding and rarely cause disease problems (FAO, 2016). In cultured fish, there is a more limited range of parasites but they are often present in much large numbers than seen in the wild. There is always a risk of parasitic epizootic in farmed fish and these increases with intensified of the fish farming system.
