The type of expert the biologist should seek is a protistologist.
Parasitic protists are microscopic eukaryotic unicellular organisms that belongs to the kingdom protista. They are capable of causing a harmful effect on any host (for example, fish) it invades.
Examples of parasitic protists include:
Protistologist are those experts in the field of sciences that studies these protists and the harmful effects they can cause to a host (fish).
The biologist having discovered that the same fish species has been dying in large numbers in other bodies of water because of an infestation of a parasitic protists, should seek the cousel of a Protistologist .
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