Leukocyte Composition of the Organs of the Immune System of Coregonus migratorius Infected with Dibothriocephalus dendriticus

For the first time, an analysis of leukocyte changes in the organs of the immune system (pronephros, mesonephros, and spleen) of the Baikal omul Coregonus migratorius (Georgi, 1775) (Salmoniformes: Coregonidae) infected with Dibothriocephalus dendriticus (Nitsch, 1824) (syn. Diphyllobothrium dendriticum) (Cestoda: Diphyllobothriidea) is presented in natural habitat conditions. In the pronephros of infected fish, the number of poorly differentiated neutrophils (myelocytes and metamyelocytes) was significantly higher than in uninfected fish, which indicated inflammatory processes. D. dendriticus triggered the immunoregulatory processes in the body of infected fish, as evidenced by the decrease in the total number of lymphocytes and prolymphocytes (B-lymphocytes) in the pronephros and the increase in prolymphocytes in the spleen. The other effector elements (cells of the monocyte–macrophage lineage, basophils, and eosinophils) were barely involved in antiparasitic defense.