Abstract
Anemia of unknown etiology has been frequently observed in Japanese flounder Paralichthys olivaceus among both wild and cultured populations in recent years. In the present study, an epizootiological research on the anemia was conducted in wild flounder (416 fish) captured in 10 different coastal waters from Hokkaido to Kyushu from February 1999 to December 2000. As a result, anemia was observed in the fish captured in all coastal waters except for Hokkaido, beeing characterized by low hemoglobin levels, low erythrocyte numbers and a frequent appearance of immature erythrocytes. In these anemic flounder (130 fish), the blood-feeding monogenean Neoheterobothrium hirame and/or its vestiges were observed at a high prevalence rate (117/130=90%) on the buccal cavity wall. There was a negative correlation between the number of adult parasites and hemoglobin levels. These results suggest that the anemia was caused by the hematophagia of N. hirame.
