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The present study aimed to identify, introduce and compare pseudoparasites in wild fish (Rutilus kutum and Mugilidae) and cage culture rainbow trout (Oncorhynchus mykiss) in the southern coast of the Caspian Sea. Wild fish specimens were collected from four stations in Anzali, Kiashahr, Chalus, Mahmoud‌abad and rainbow trout in three cages of Kiashahr, Abbas‌‌‌‌‌abad and Si-Sangan. After transferring the specimens to the laboratory, they were bio‌assayed and parasitological examination was performed on all internal and external organs. Free-living nematodes, pine pollen, pollen grain, protozoa, fungal spores, plant seeds, and filaments were isolated from fish as pseudoparasites. The highest percentage of pseudoparasites belonged to Pine pollen and was found in almost all fish organs. Free-living nematodes were isolated from the stomach, intestine, gills and Pollen grain from the liver, spleen, and kidneys of fish. Pseudoparasites are widespread in addition to they may be transmitted by food or randomly to fish. Pseudoparasites do not cause infection and disease in their host. Investigating and understanding them because of their importance in the parasitology can be useful for parasitologists and fish farmers to avoid the futile consumption of pharmaceuticals.