In the mid-1990s, wild olive flounder showing heavy anemia characterized by deformed erythrocytes with low-stained cytoplasm appeared in Japanese waters. Parasitological, histopathological and hematological studies and surveys revealed that the anemia was caused by the infection with the monogenean Neoheterobothrium hirame on the gill and buccal cavity wall of host. The parasite was later revealed to originally infect southern flounder Paralichthys lethostigma in north America and invade Japanese waters. Bathing in NaCl-supplemented seawater is effective to remove worms from fish. The parasite has been prevailing in wild stocks of olive flounder and may threat the stocks especially in warmer waters.
