Epizootiology of anemia in wild Japanese flounder

Anemia of unknown etiology has been frequently observed in Japanese flounde r Paralichthys olivaceus among both wild and cultured populations in recent years. In the present study, an epizootiological research on the anemia wa s conducted in wild flounder (416 fish) captured in 10 different coastal wa ters from Hokkaido to Kyushu from February 1999 to December 2000. As a resu lt, anemia was observed in the fish captured in all coastal waters except f or Hokkaido, beeing characterized by low hemoglobin levels, low erythrocyte numbers and a frequent appearance of immature erythrocytes. In these anemi c flounder (130 fish), the blood-feeding monogenean Neoheterobothrium hiram e 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 n umber of adult parasites and hemoglobin levels. These results suggest that the anemia was caused by the hematophagia of N. hirame.